(first posted 8/31/2012. Revised 6/6/2016 and 6/6/2022) Overdrive. For you younger readers, no, we’re not talking about the top gear in modern stick-shift or automatic transmissions. This is about epicyclic or planetary overdrive (not interstellar overdrive, which also has its joys), as pioneered by Borg-Warner in 1934, and available on various American cars and trucks with three-speed transmissions until 1976, when the last AMC Gremlin or Hornet free-wheeled off the lines with one.
Perhaps surprisingly, this overdrive wasn’t solely to reduce engine revolutions on the highway. It was designed to reduce the need for shifting and clutching, which was considered tedious, especially by women; in other words, it was set up to be essentially a semi-automatic transmission, to make driving more effortless.
Borg-Warner’s “automatic” overdrive premiered on a car that was quite advanced and adventurous in other ways: the 1934 Chrysler and DeSoto Airflow. Chrysler engineer Rex Keller is given credit for the creation of “the Keller clutch” (overdrive), but to avoid the $25,000 cost in in tooling for it, Walter P. Chrysler chose to have Borg-Warner make and supply it. That allowed competitors to also buy the system.
It would be natural to assume that Chrysler chose to take of advantage of this new technology because of the Airflow’s other technical advances and presumed higher cruising speed, thanks to its aerodynamics. But there was also another one.
In the twenties through the forties, American cars (and their drive trains) were designed for the prevailing conditions, which were very different than more modern ones. Towns and cities were compact and dense. Everyone still knew how to parallel park, even. Trips were typically short, with lots of starts and stops.
Highways were narrow, often with steep grades and tight curves. Highway speeds were typically around 45 or so; lower on lesser roads. Higher speed parkways and throughways were just emerging in the largest cities. Cars were geared to these conditions, with very low (high numerical) rear axle ratios, typically between 4:1 and 5:1. Combined with long-stroke engines that preferred to run at low rpm, most cars really weren’t happy above 50 mph or so, except for short bursts.
The other key factor in drive train design was that transmissions were balky. Cadillac had the first syncromesh transmission in 1929–only on the second and third gears–and it eventually spread throughout the industry. Even with syncromesh, down-shifting into first meant either coming to a full stop, or deftly double-clutching. That would be the norm until well into sixties.
Although a substantial improvement over the crash-boxes before, these early syncromesh transmissions were hardly a joy to shift, never mind the heavy mechanical clutches. Women in particular were none too thrilled with that whole aspect of driving. The search for clutch-less and automatic transmission solutions had a strong motivation.
There were many approaches to this problem, and the fully automatic transmission was the Holy Grail. GM’s Hydramatic of 1940 got there first, but it was complex, thus expensive. Meanwhile, other solutions arose, like Chrysler’s two distinctly different Fluid Drives, which first appeared in 1939-1940.
But even simpler and cheaper part-measures also abounded. This included free-wheeling, which allowed the car to “coast” whenever engine speed dropped low enough to not actively power the car. This also enabled clutchless shifting, as freewheling had the same effect as disengaging the clutch, but on the other end of the transmission (output shaft instead of input shaft). But the danger of cars outrunning their brakes on long downgrades soon put the kibosh to that. “Automatic clutches” had a vacuum servo that sensed when the driver was about to shift, and obliged him or her by disengaging the clutch–as long as it was adjusted properly. Both had a short life.
Borg-Warner’s planetary/epicyclic overdrive is typically thought of as affording only the benefit of lower engine speed on the highway, and that it did admirably, offering a 30% reduction. A 1934 Chrysler Airstream really hustling along at 75 mph reduced engine speed from a near-redline 3780 rpm to a much more tolerable 2650 rpm.
But the other benefit was in essentially eliminating shifting altogether in town driving. With Overdrive? How’s that? Because most cars had such low gearing, starting out in second was completely doable and fairly common on flat terrain. At above the minimum engagement speed of 20 to 32 mph (depending on the car’s settings), a quick lift up on the gas pedal caused the overdrive to kicked in, creating a gear ratio(2-OD) almost perfectly spaced between normal second and third, an ideal gear ratio for cruising on typical city/suburban roads in the 20-35 mph range. A stab on the gas pedal resulted in a downshift to second-direct, for passing or hills. Or if the car slowed down below the governor speed of 20 to 32 mph, and the gas was eased up a bit, it would also shift back down.
And there’s more: if a rolling shift into (unsynchronized) first is necessary, the shift was also easier with less tendency to clash, because the combination of the clutch at the front and the freewheeling on the output shaft meant that there were no forces acting on either shaft that had to be synchronized. And if one had a bit of timing, the shift to first could be made without pressing the clutch at all.
My ’66 Ford F-100 was originally built with Ford’s new all-syncro three-speed manual. When that transmission died a couple of years after I bought it, I wanted an overdrive, and I knew a transmission guy in the neighborhood who was familiar with them and had a few out back. For simplicity’s sake, we didn’t replicate the vacuum/electric system for “automatic” functioning. Frankly, I prefer it that way, having full (manual) control of the OD in all gears. Initially, I used it only on third gear on the highway, ignorant of its full potential.
Some years later I read a very detailed article on the B-W OD (highly recommended for all the details I can’t fit into this article) and I totally changed my habits. Now I have OD enabled all the time except when I want to avoid freewheeling while in a direct gear going down a grade (there is no freewheeling when in any OD gear). And I only use the clutch for starting and stopping: all my other shifts, up and down, are made without the clutch, thanks to the freewheeling acting like a clutch, even if it is on the other end of the transmission. This is not like the typical clutchless “float” shifting, which requires engine speed matching; these shifts are clutchless because of the freewheeling. Many comments on this YouTube video of me driving my F100 insist that I’m just “float shifting”, but I’m not. I can shift up without waiting for the engine revs to drop, and more importantly, I can downshift just as easily. You can’t do that with float-shifting.
My truck has five very nicely spaced gears, and I use them all regularly. Most of all, I use second-OD when puttering in town, as its perfect for the typical 25-30 mph zones. American three-speed transmissions tend to have an overly large hole between second and third; in town one is either revving faster than necessary, or chugging. And when I regularly hauled a load and a trailer between Oregon and California, second-high was perfect for the steepest sections of I-5, which my truck couldn’t take in third before.
The BW OD, typically R11 and R12 units in modern times, sits behind the legendary BW T-85 (or related variants) transmission. The round object projecting from the side is the speed governor/solenoid, that allows OD to engage at 28 mph (in the modern era). As such, OD is realistically available only on second and third. With my manual set-up, I can engage OD in any gear, although first-OD is so close in gearing to second-direct, I hardly ever use it, except to avoid shifting if I’m in stop-and-go traffic or one of those residential streets with a stop sign at every block.
I’m not going to do a detailed mechanical and electric explanation of the BW OD here. The article I linked to above is excellent in covering the basics of its design and operation. And if you want more detail, here is a pdf of Borg-Warner’s original manual. A great read, if you go for such things.
Another significant benefit of the B-W OD came into play during the early years of the high-performance era, prior to four speed manuals becoming readily available. The tri-five Chevys with their high-revving V8s were unbeatable on the street or strip with the right rear gears. Ordering the the optional overdrive behind the three-speed transmission allowed one to specify a very low (high numerical) rear axle ratio for maximum acceleration, especially on the drag strip. 4.11 0r 4.56 gears were almost impossible to live with on the freeway, but OD made that quite possible and very livable.
Overdrive was not consistently available on all cars; in fact, none of the GM divisions except Chevy offered it, and then only after 1955. Ford started earlier, in 1949. Somewhat oddly, Dodge and Plymouth shunned OD after the late fifties, perhaps because they were so invested in their excellent Torqueflite automatic (which did not have an overdrive gear). The independents were the most consistent and enthusiastic OD users, which played to their thrifty and practical sides. AMC and Studebaker both marketed overdrive more aggressively, as it suited the economy-orientation of many of their buyers.
The reasons for the decline in the popularity of overdrive were several: automatic transmissions became ever more popular. And as engines became more powerful, overall final drive ratios kept lowering (numerically), reducing engine revolutions on highways, at least to more reasonable if not optimum levels. Gas prices dropped (in adjusted terms) throughout the sixties, through 1972. It simply lost its appeal.
Ford offered their last passenger car OD units in 1964, and kept it available on pickups until 1972. Chevrolet’s last year for cars was 1968. AMC brought back the three-speed and OD combination as an option on its smaller cars (Gremlin, Hornet) in 1975 and 1976, undoubtedly in response to the energy crisis. It was gone again in 1977.
After the first energy crisis, everyone was in desperate rush to get gas-saving overdrives back, but now the expedient solution was to use a four speed manual altered to have an overdrive ratio on top gear. Worked, but not as elegantly as the BW OD, and not nearly as much fun to drive, especially the part about having to use a clutch. And of course, five-speed manuals with overdrive top increasingly became the norm, and automatics also sprouted overdrive top gears.
Postscript: In Europe, the rather similar Laycock-deNormanville epicyclic overdrive went into production in the 1940s, and was widely available on many British cars as well as Volvos. In the US, Gear Vendors has been building and selling an updated version of the B/W unit for decades, also available in an underdrive.
So how does this all relate to the Gear Vendors unit that is familiar to most modern hot rodders, RVers, and towing junkies?
The Gear Vendor unit is pretty much the modern decedent working in a similar fashion.
Never heard of Gear Vendor…I need to look that up.
The Gear Vendor overdrive was patterned after the English Laycock de Normanville overdrive. It is much better than the more common Borg Warner overdrive because it will shift under power and has no freewheeling. You flip the switch and it sounds like an automatic transmission upshifting.
Gear Vendors got their start by buying left over Laycock-DeNormanville OD units from AMC, who used them in the mid 70s in Hornets and Pacers with their 232 and 258 six and a three speed manual trans. GC later bought rights to manufacture and made a bit heavier duty unit. The LD (and GV) units use a hydraulic unit to shift into and out of OD, the electric solenoid is just a fluid valve. The way the gears are made is why it can shift under load. As far as I can tell both the LD and BW units use the same type planetary gear set, but the LD unit has much large planetary gear shafts. I do know from experience that the planetary shafts are what eventually break if you down-shift a BW unit under load — I wired one up with just a toggle switch when young and just let off the gas when down-shifting. After a few weeks it broke! When a planetary shaft breaks it just jams that gear between the outer ring (“drum” gear) and sun gear, locking the input and output so it’s just a straight three speed. Sounds like a shot gun fired under the car, but at least you’re not stranded.
The 1957 Chevy I attempted to restore in the mid-70’s had an overdrive tranny. Too bad I never got a chance to try it out, as I sold that car in boxes in 1979….
My 1980 Dodge truck and my 1976 Dart Lite both had three-speed sticks with 4th an overdrive. They worked well.
Those Dodge gearboxes were really a modified 4 speeds. The “fourth” gear was 1:1 and “third” was an overdrive ratio. The shift lever was flipped 180 degrees, so when you shifted up through the gears, you went 1st. 2nd, 4th, 3rd. (compared to the usual 4 speed setup).
It was quite ingenious!
I believe that the 4 speed overdrive manual that was available in the early to mid 1980’s Chevy and GMC full sized pickups was actually sourced from Chrysler…..
It’s certainly possible. Even the major car manufactures sometimes didn’t make their own transmissions, either manual or automatic.
I had four cars with OD but only two of them worked. The +/- 25% OD attached to the rear of the Spicer (Dana) T18 transfer case was a virtual necessity. With 5.38:1 gearing, even with 16″ tires, 55mph was a struggle in direct drive. The system was mechanical, only worked in 2WD and a version of it is still being offered.
#2 was a bit more exotic; an electric OD in an Austin-Healey 100-4. The on/off switch was on the dash and the in/out toggle was on the shifter., so 1-2-2OD-3-3OD was rapid and smooth… until the famous English electrical system went south for the winter.
#3 and 4 were a ’53 Ford Customline and a ’47 Studebaker Champion, both 2 door models. Neither had a working OD. I wanted to fix the OD but was talked out of it for three reasons: 1) fixing would be too expensive. How someone could know that without diagnosing the problem is beyond me now, but then I was just a trusting kid. 2) OD systems were unreliable and the fact that these were inop was proof of that. 3) “experts” told me that the OD systems were weak due to the planetary gearset and that was probably the cause of the OD units to be inop. So, both cars went off still with non-working OD and I never got the chance to see what was wrong or how well they operated.
I still don’t know about the alleged lack of strength. Since I like to tow things that could be an issue but probably one I won’t have a chance to face.
My father had a 1953 Austin Healey with the Laycock de Normanville overdrive. At that time, the OD had a toggle switch on the dashboard. That made split shifting, i,e., 2nd, 2nd OD, 3rd, 3rd OD impossible. I never happened to see one with the OD switch on the shift lever, but that would have made split shifting practical.
Regarding the Borg Warner OD, which was quite common and my 1951 Ford had one, the most common failure was electrical and could usually be fixed at little cost. On mine, when the OD failed, the dealer immediately, without checking it, stated that it needed a new solenoid, which was somewhat expensive. When I suggest properly diagnosing the problem before changing parts, the service salesman ridiculed me. I was just a 20 year old kid who presumably new nothing. They changed the solenoid, but the OD still did not work. It turned out to be a defective kick-down switch which cost very little and was easy to replace.
So, no assumptions should be made about the reason that an OD has failed. Instead, it should be checked out electrically, which is not difficult, to determine whether it is an easily fixed electrical problem.
The OD solenoid had 2 coils: A strong high-current coil to pull in the plunger, and a weak low-current coil to hold the plunger in. When the plunger was pulled in, a pair of contacts opened to cut off the current to the high-current coil. The contacts had a limited life and there was no provision to replace them, so normally the entire solenoid assembly was replaced. It may be that someone has found a way to replace the contacts. If it is possible to get into the solenoid assembly (that might require cutting), the life of the contacts could probably be extended by connecting a free wheeling diode across the high-current coil to suppress the arc across the contacts.
The fault was invariably in the solenoid or related electrical system. The basic planetary overdive unit was very rugged. Lots of mechanics didn’t understand how they worked and didn’t want to work on them.
Paul, considering that the OD circuitry was actually quite simple, what you wrote seems very strange. However, it also seems true based on my experience from way back in 1959. At that time mechanics were often not very well educated and had little understanding of electrical problems. Even so, I think that an hour or two of classroom instruction would have been sufficient for them to learn how the OD electrical circuitry worked and how to diagnose problems. A person familiar with electrical circuitry in general could easily figure it out within a few minutes from a schematic.
Regarding the ruggedness of the mechanical parts, OD was available on some cars with very big engines, including the Packard Custom Eight with its 356 cubic inch engine. Considering that most cars had much smaller engines than that, the ruggedness of the gear system should certainly have been adequate for them.
Another problem was that most drivers did not adequately understand how to use the OD. Many thought that to lock the OD out or to enable it with the handle or knob under the dashboard the car had to be standing still. Actually, that could be safely done with the car moving as long as it was under power with the OD disengaged.
I really think that a 4-speed transmission would have been better than a 3-speed transmission with OD, but it seems that American drivers saw 3 speeds as the “correct” number of speeds and wanted nothing to do with 4-speed transmissions.
Most of the electrical troubles are due to burnt or corroded points in the relay, governor, or solenoid. Easy to clean them, and the other wiring connections should be cleaned also. Increased resistance leads to burned points..
Also, you state: “The round object projecting from the side is the speed governor/solenoid, that allows OD to engage at 28 mph (in the modern era).” The governor sticks out on the opposite side of the OD. There are two different governors — a single connection and a dual connection (at least as used by Rambler). The single grounds through the governor body. The dual connection doesn’t ground, but is used to complete the connection from the solenoid. With the dual connection governor no OD relay is needed. Rambler used the dual connection (and no relay) in the 64-69 American, and 65-69 big cars. Earlier models used a single connection governor and relay.
A fascinating piece. I had always known about OD, but never about the freewheeling/clutchless shifting functions of the BW unit. Of course, I never drove one of these.
Fords of the torque tube era could be fitted with a 2 speed OD axle manufactured by Columbia, which was a fairly popular accessory in the 1930s and 40s. Also, the guy with the 365 Days of A website (who drove a Model A as everyday transportation for a year) fitted his A with an OD unit that was basically a 2 speed transfer case that required cutting the torque tube and replacing the driveshaft. The unit mouned under the front floor and a control lever came up through the floor. But both of these lack the elegance and added functionality of the BW unit.
Now you’ve done it – you have gone and added one more thing to the already crowded list of things I want to experience.
Overdrive is a particularly popular upgrade to As. They have the power to cruise at 55-60, but need to keep the revs down. There’s a number of different ways to go, including splicing in a BW unit into the drive shaft.The A I shot for my CC had a OD unit too.
Here’s a BW OD as spliced into a Model A drive shaft:
In November of 1950, Arkie Shibley and his Mountain Dew Boys released a Western Swing single called “Hot Rod Race”, about a Ford and a Mercury racing out of San Pedro, ripping through little towns heading north towards the Grapevine.
If you listen to the lyrics, the words are very accurate about describing early speed part trends like twin carbs, dual exhaust, and a Columbia two speed rear end, described as , “got a Columbia butt”, meaning a Columbia overdrive but the songwriter apparently needed to rhyme word for rut!
I drove a Dodge colt at work many years ago that had a “super power shift” lever next to the normal shifter which was basically overdrive. If you were quick with both shift levers you basically had an 8-speed trans. Gear Vendors can achieve the same effect with some electronic gadgetry, doubling the number of usable gears of your current slushbox.
Yup- the Mitsubishi Twin Stick. I had an 83 Colt (a Plymouth Colt, no less) with this tranny. I used mine as a 5 speed – low range through all 4 gears, then shift the other lever to high range, which made for an OD 5th gear. I believe that some Ramblers used a similar setup in the mid 1960s. It seems like an effective solution, although is probably more expensive than just engineering another gear into a transmission.
The mitsu twin stick is a little different in that it engages two different final drive ratios making it closer to a 2sp axle in basic theory. It was best used as a 5sp and that is what it morphed into when installed in the Excel/Precis. A vacuum motor, switches and relays replaced the second stick. An internal modification was done that allowed that “5th” shit position that still engaged direct drive or “4th” and activated a switch that engaged the second axle ratio or OD if you prefer.
Another example of the concept is some of the modern 6sp manual transaxles like used in the Focus SVT which essentially was a 3sp transmission with 2 separate final drive ratios.
The basic OD set up is used in some modern ATs to achieve the 5sp and 6sp configurations. For example the Ford 5sp 5R55E gets it’s additional ratio vs the 4R44E by engaging 2nd and OD.
The Rambler “Twin-Stick” of 63-65 was a BW OD unit with the lock-out moved from a handle under the dash to a second lever to the right of the three speed floor shifter in a console. A bit more to it than just that — the three speed trans had a big “gap” between 2nd and 3rd, allowing it to be shifted as a five speed, though not a real quick shifting one. The kick-down switch was moved to the top of the three speed shifter so it would engage when you put your hand over the knob to shift. The electric controls were modified from a typical OD unit to facilitate five speed shifting. A normal three speed (at least as used in Ramblers) didn’t have enough difference between 3rd and 2nd+OD to be practical to shift five forward gears.
I did neglect to give the Twin-Stick Rambler sufficient recognition.
Are you quite certain about it having a different second gear ratio? All American three-speeds had a pretty big gap between second and third; I always use 2nd OD in my F100 when shifting up through the gears.
The reason that all American 3-speeds had a big gap between 2 and 3 was that the gap between 1 and 2 was small because 1 was not synchronized. Thus, when drivers had to slow down to perhaps 3 mph and didn’t know how to double-clutch, they used 2nd gear so 2nd had to have enough reduction to make that possible.
However, there was a change. My mother’s 1958 V8 Chevrolet with 3-speed transmission had a very small gap between 2 and 3. The ratios were the same as the Corvette 4-speed but without 2nd gear. The Corvette rations were about
2.21:1, 1.7:1, 1.32:1, and 1:1. Sedan ratios were about
2.21:1, 1.32:1, and 1:1. Oddly, if the Sedan was equipped with the optional OD, it didn’t have the close ratios if I correctly remember.
To figure out how fast one could go in the gears on the Sedan, I divided 120 mph by the ratios and came up with 54 mph in 1st and 91 mph in 2nd. Thus 2nd made a very good passing gear for highway use. Of course it was a bit slow accelerating from low speeds in 2nd.
AMC Twin Stick
Maybe this one will work.
“Ford didn’t have a four speed until 1962. Ordering the super-tough BW T-85 with OD allowed one to specify a very low (high numerical) rear axle ratio for maximum acceleration, especially on the drag strip. But 4.11 or 4.56 gears were almost impossible to live with on the freeway, so OD made that possible.”
Lyrics to “Hot Rod Lincoln”, written by Charlie Ryan (his real car shown below):
It’s got a Lincoln motor and its really souped up
And that model A body makes it look like a pup
It’s got eight cylinders, uses them all
It’s got overdrive, just won’t stall
It’s got a four barrel carb, and dual exhaust
With four eleven gears you can really get lost.
It’s got safety tubes, but I ain’t scared
Brakes are good, tires fair
As a kid I had a record of the Johnny Bond version of the song from about 1961 or so. Still have it. I played it so much you can barely understand any of the words now.
Try the nine-minute Bill Kirchen version – you’ll be blown away!
I remember his version on KFAT from Gilroy. Ah, the good times.
Both of my British cars had electric OD on 3rd and 4th. The TR3A had an odd switch that seemed to offer a delay–couldn’t find any details on it, and it was a scary thought to open it up for checkout. The MGB used a vacuum cutout so the OD would stay locked out until you let up on the throttle (memory is a bit fuzzy, haven’t owned it for 39 years…). Both OD units were effectively integral with the transmission. I know the B’s was a planetary, and assume the Triumph was the same way.
I heard the original lyrics was it also had a Lincoln twelve
I don’t know for certain about the Lincoln V12 although I think it was available on the V12. It was available on the flathead Lincoln V8.
Both overdrive and a two-speed axle were optional on the Lincoln-Zephyr and Continental, and for at least a brief period you could theoretically get both. I’ve ridden in (but not driven) a ’39 Zephyr with overdrive, which is a good combination.
Hard to imagine asking modern drivers to learn anything so complex. (Then again… Ford Sync!)
I used to have a Honda CB1000C, with a 5×2 transmission. I just used it as a 6-speed–no need to split gears when you have a 1000 cc engine. (Would’ve been much more appreciated on my earlier CM400T!). Anyway, a paragon of simplicity compared to this BW overdrive. I’m endlessly fascinated by how simple and standardized driving has become.
That Honda 2-speed gearbox was put in there because they had the space due to changing the rotation to the shaft drive. I knew a few people who had the bikes, almost all of them just put the x2 transmission into the high range and left it there.
Suzuki also had a dual range transmission on some dirt/street bikes about 1970.
Top photo – I’d recognize a Tri-Five anywhere.
Great story!
Fascinating article, especially given the fact that my first car a 1956 Plymouth Savoy had a three speed transmission with overdrive.
I’m not entirely sure , but I believe it was this same BW electric unit.
I distinctly remember letting off the gas at about 30mph ,then feeling the overdrive engage.
I also remember the “freewheeling ‘ aspect of the overdrive ,which I thought was cool.
As a 16 year old I thought I knew and had done everything possible with that car. I must confess though that I had no idea that you could use the overdrive as stated in the Borg Warner overdrive link .
my mom’s ’83 volvo 240 had a 4 speed automatic with overdrive. the overdrive was a little “od off” button & led on the shift knob. i asked my dad what it was and he said it’s like fifth gear on his fiat. i now know that is incorrect but please don’t test me on the material above. my mom never touched the button. i had a lot of fun using that button as if it were a 5th to 4th gear downshift control until one day it didn’t go back into overdrive. fortunately, my mother never noticed and my father didn’t drive the volvo. a few weeks later, i was greatly relieved to see that the car had somehow gone back into overdrive. i never touched the button again.
In a number of years the Volvo OD units were actually supplied by Gear Vendors and uses a similar design as the BW unit.
Ive been battling the high numerical diff ratio in my Hillman as being a 59 it was designed before England had motorways and 100kph cruising was painful on the low profile tyres Im using diff ratio 4.55:1. An overdriven Hillman box can be got reconditioned for $750.00 out of my meagre price range so Ive fitted a 3.89:1 diffhead and axles from a 65 Minx they were motorway capable like the recently featured Rapier and my car now cruises quietly at 100kph/60mph with the 205/60/15 tyres which give it cornering ability equal of most modern cars and the best part the parts were free from a friends wreck collection
Very good – and relevant to me – article. I used some elements of the three-speed with overdrive in my ’63 Galaxie back in the late ’80’s. Now I just have to get it going again which is another story in and of itself.
I used to think the three-speed manual was a real snoozer of a transmission, but I have been thinking otherwise the last several months.
UPDATE: Having the Galaxie I referred to nearly four years ago back on the road for nearly three, everything Paul says here is spot on. Second o/d is a fantastic gear for around town or merging onto the highway. First o/d is nearly useless and third o/d helped me get nearly 21 mpg on a highway trip – in a car powered by a 352 FE. If looking for an older car, try to find one with the three-speed with overdrive as it gives a much richer driving experience.
Actually, I would have preferred a 4-speed transmission to an OD. I think that the real reason for the OD was that American drivers saw 3 speeds as the correct number of speeds and that there was something bizarre or wrong with a car that had more than 3 speeds. Here’s a story to support that.
Hitler’s 5-speed Mercedes was being taken around the U.S. to show it off as a curiosity. A newspaper reporter drove it. He wrote that although it had 5 speeds, it was possible to drive it like a 3-speed car by not using 1st and 5th.
Another story. A friend of the family had a Mercedes 180 with a flat head 4-cylinder engine and a 4-speed transmission with the shift on the column. When my mother tried it out, the family friend suggested that she drive it like a 3-speeder by starting in 2nd. Mother later said that starting in 2nd didn’t feel right when she did it once so after that she started in 1st.
You may have seen the movie “The Graduate”. In it, the Graduate asks Mrs. Robinson whether she can drive with a foreign gearshift; he had an Alfa Romeo which had a 5-speed transmission. Mrs. Robinson responds, “Of course not!” So, the Graduate had to drive her which led to the affair.
No doubt a four-speed would have given a different flavor.
However, seeing as I obtained the car when it was 23 years old, it’s not like there was much choice. Besides, given what Ford was offering at the time, and this is a four-door sedan, this was the best overall option. 🙂
Considering the situation, probably you made the best choice. I wasn’t questioning it. It’s just that I think that for the auto industry, it would have been better to use 4-speed transmissions. I think that the public could have been induced to accept them.
Peugeot at one time had a 4-speed column shift in which reverse and the 1st three speeds were exactly like a 3-speed transmission. 4th gear was forward and up. So, driving in slow traffic, a driver could use it exactly like a 3-speed transmission and use the “weird” position and gear only when driving a bit faster. I drove one of those Peugeots once and was impressed with how easy it was to shift.
And I must say Jason, you haven’t aged a bit in four years!
Well, a typical 4 speed would have added an intermediate gear, but no overdrive gear for reduced engine speed on the highway. To get the benefit of OD, a 4 speed would need to either be used with a very low (numerical) rear axle, or be set up like those odd Chrysler 4 OD four speeds from the late 70s early 80s. But when you do that, you lose the benefit of the extra intermediate gear.
The reality is that a car really wants to have 5 gears, and a 3 speed w/OD gives that, which is really better than a 4 speed. But it’s not quite as simple to operate.
I would never upgrade an older American car from a three-speed to a 4 speed; I’d go right to a five speed, like a T5 or such.
The big advantage of three-speed plus overdrive, of course, is that it made the extra gears an extra-cost option with much lower tooling costs than an a gearbox with additional speeds. Obviously, manufacturers have contrived various ways to turn a three-speed into a four-speed or a four-speed into a five-speed, but I think that was more common for transaxle applications where there wasn’t room to just stick an accessory overdrive behind the transmission.
My ’13 Beetle had a six-speed manual, which was really “one too many.” It really was more like a five-speed with overdrive; I never used sixth unless I was on the interstate doing 65 or higher.
The 6MT Honda Fit I drove on test drive had horrible ratios – you rowed like mad up to 40, where fifth was the comfortable gear. That left you with only one more gear for higher speeds, which resulted in a rather frantic engine note on the interstate. An OD would have been much preferred. That’s the main reason I bought the CVT.
As a past Honda owner, I’ve experience and been annoyed by their penchant for ridiculously short final drive ratios. (They don’t always do it, but when they do, it’s kind of insufferable.) Close-ratio gearboxes might make sense for racing, but if you’re going to have five or more ratios for a street car, it seems reasonable to expect at least one of them to be a decent highway gear.
I remember driving a mid sixties falcon convertible with a 289. It had the most satisfying clunk when the overdrive kicked in.
In driver training class (1975) we were admonished to always lockout the overdrive in wet or icy weather.
Did they explain why the OD should be locked out in wet or icy weather?
With rear wheel drive, a little engine braking allows the car to slow stably, with less need to apply the brakes.
I remember mountain summit roads in the 60s often had a sign at the beginning of the descent telling you to disengage overdrive.
I have heard of these, but, never have gotten such a good explanation of how they worked. I’ve been looking at four speeds and a different rear end to solve a problem. I may make a few junk yard calls this weekend!
Thank you for the lessons in a type of transmission I’ve never had experience with. Sounds like an elegant solution for a problem that exists at one time. Nowadays manufacturers would just as well put a 6-speed tranny rather than a separate OD system, so unfortunately it’s not likely to come across this type of tranny in the future…
My sister’s ’75 Volvo 240 had a 4 speed manual with an electric overdrive switch on top of the shifter. It knocked about 400 rpm off the engine speed when it came on.
How does the Borg-Warner overdrive compare to the Bachman-Turner Overdrive?
Quieter, less bass.
+1
+2 😀
+3 (:D
really takes care of business…
Sorry.
The British loved their overdrives. Up until recently GKN made an electric OD unit for Landrover Defenders, but the factory 6 speed seems to have killed it. You can still get the Rocky Mountain manually shifted planetary OD units for various Landrovers plus the old Fairey units with conventional gears are still easily found and fixed.
You know, Paul, I remember Massey-Fergeson tractors of a certain vintage had a “Multi-Power” transmission system that functioned similarly. In addition to the usual crash box, it had a low-high range lever that you could shift on-the-go, I believe with freewheeling in the low range. It was handy if you were hauling a load downhill in low range, and when the load started to “get away from you” rather than trying to engage both brakes equally (each rear wheel had it’s own pedal), you could switch to high range and engine braking would take over, without overreving the engine or putting too much strain on the transmission. I used it mostly when driving the baler tractor, as you could run along in the low range and switch to high without having to stop and clutch (and risk a comment from the stackers on the wagon, who didn’t understandably didn’t like being jerked around) when you hit an area without very much hay. I wonder if the “Multi-Power” system was another name for a Borg-Warner overdrive. I shall have to study up on this-thanks for a most informative entry.
Oh-and my vote for favorite version of “Hot Rod LIncoln” goes to Commander Cody and the Lost Planet Airmen, from the Hot Licks, Cold Steel and Other Truckers’ Favorites album.
Not sure about the Masseys, but a fair amount of tractors still have a high-low range after the transmissions. My little Deere 790 has 4 x 2, and can go from about 0.9 mph (in low 1st) to 11 (high 4th) with the dual ranges at max (nominal) throttle. International offered a “Torque-Amplifier” system, sounds a lot like the MF one.
Fergies and Ford 8Ns could be fitted with an aftermarket 3-range transmission. I was told by a Fergeson owner that he could go about 35MPH in top range. Fun if you like tractor racing, I suppose. I had the Deere on the road at 11mph once and it was more interesting than I ever wanted to experience again. (High center of gravity, very short wheelbase, and fast steering. Did I mention no suspension?)
The International “Torque Amplifier” appears to be very similar, except it worked as an underdrive, allowing “downshifts” without any clutching. That was areal boon, when things got a bit tough or steep in the field, instead of having to stop and shift down. And yes, they did freewheel with the TA engaged, as I found out in a very scary situation myself once, on a long downhill road with a steep turn at the end. Thought the TA would slow me down; it was quite the opposite.
My Allis-Chalmers 190 had a high-low “Power Director,” which worked great while baling, as you could bump between third and forth without hitting the clutch (it basically turned a four-speed into eight, plus two reverse gearings).
Dang Paul, I never knew that stuff. I had a 68′ Volvo with manual trans and overdrive, never knew how to use it. Now I have an 87′ Volvo with auto trans and OD, I just leave it engaged. It’s not often I learn about some mechanical thing I should be familiar with that I’m not, thanks!
I know British automakers frequently offered various Laycock de Normanville overdrives, which in some versions could be used on everything but first (a TR4 with overdrive effectively had seven speeds, although whether they were all useful is debatable). What I confess I’m not sure about is how common overdrive was in other European markets prior to the 70s. I know some Volvos offered it, but I’m trying to think of a 50s or 60s German or Italian car that did: four- and five-speed gearboxes, sure, but not LdN/BW-style overdrive units.
It wouldn’t necessarily surprise me if overdrive was more popular in the U.S. and U.K., just because both markets had a fondness for engines with long strokes and lots of low-end torque. (The U.S. hadn’t fully embraced the oversquare format until the mid-50s and a lot of sixes were still pretty undersquare, with torque peaks in the 1,200-1,500 rpm range.) With a big 3-liter or 4-liter straight six, overdrive makes a lot of sense; with the tiny Italian engines that had no discernable torque below 3,500 rpm, perhaps less so.
One day I should go through the technical materials and get some sense of the differences between the Borg-Warner unit and the various Laycock de Normanville ODs…
Oh, side note about the Airflow; The reason Chrysler adopted overdrive was because the Airflow cars ended up substantially over their target weights and were actually quite a bit heavier than the conventional cars they replaced (comparing the shipping weights of a ’33 Chrysler or DeSoto with the Airflows is an eye-opener). Overdrive offered a way to keep fuel economy within reasonable limits without getting into a lot of expensive and time-consuming engineering changes.
Good point. I can’t think of any German or Italian cars with overdrive. They tended to design their engines to be more suitable for high speed use.
Early ’60s Ferrari 330 America could be had with a Laycock overdrive (Tom Yang Ferrari Repair website – his has one)
Thanks for re-running this, I’ll have to sit down some evening and go through how the BW unit works.
My childhood friends father raced a TR4 in the 60’s, he told me that having the Laycock overdrive was a great advantage in racing because it shifted under load and you could keep the engine in the torque peak more.
Aaron I hadn’t seen your comment before I’d written the one below – I think European makes typically had four gears in their gearboxes to start with, meaning less requirement for overdrive which they added as an extra (5th) gear from the early 60’s.
Often the English overdrive worked on 3rd & 4th gear, but the rally teams modified this to work on all gears.
The Hillman Imp runs a 0.85 fourth gear ratio, but the final drive ratio is 4.86:1 so it does 15mph per 1000rpm (4000 at 60mph). The close ratio set in my Imp puts it at closer to 5000, I have a couple of other gear ratios, but the Imp is quite rev-happy, my other Imp (also modified) sat on 6000rpm/90mph easily. I wouldn’t mind a fifth gear though to cut down the noise a bit.
It’s true that the European makes were more likely to have four speeds forward, although the British sometimes seemed to fall into the trap of making first gear so impossibly short that it was functionally useless much of the time — the same thing that doomed the handful of American four-speeds in the early 1930s. Perhaps the most notorious example is the Austin A90 gearbox, whose low ratio was so short that when the engine and gearbox were transplanted into the Healey Hundred prototype, the Healeys opted to just block off first and make the transmission into a three-speed (with standard Laycock de Normanville OD).
Hillmans and a Austin I had have a switch on the shift mechanism that switches the overdrive on all you have to do is bridge those two terminals and you have 8 forward speeds my 55 A90 westminster was set up that way but the torque in first and second wrecked the overdrive unit, shame because it was fun, wind it up from a traffic light hit the redline and punch the od in an instant extra 500 rpm, with a 2.6L six and twin SUs twin branch factory header and straight thru exhaust it was quite a quick car.
My codriver and I ran a Volvo 142 on the Road Rally circuit in Ontario back in the early 80’s. We scrounged an OD out of a Volvo wagon. This used to be controlled by a button on the shift knob thru a detent switch on the trans that allowed the use only in 4th gear. We removed the detent and installed a microswitch at the back of the shift rods that would simply lock reverse out of the equation. Then we installed a red ‘splitter button’ on the side of the shifter to activate the OD unit. (Down being on, up being off) On take off, you would pull the button up, stand on the throttle and dump the clutch. When the revs came up, you push the button and go into 1st OD. Revs up, shift to 2nd and simultaneously push button. Revs up, pull button and repeat. Effectively made an 8 speed. Acceleration was wild.
Very interesting Paul. I haven’t come across one of these, just the Laycock de Normanville type on Sunbeams etc plus other British makes, and 2 speed axles in trucks.
I love overdrives, and both of my cars have Laycocks- interestingly one of the first and one of the last. My p4 Rover has an overdrive that has (had) one of the most complex almost rube goldbergian systems. There was a lever on the column to switch overdrive on and off- as with most cars. Additonally, there was a kickdown button under the accelerator to drop the overdrive out for passing. Very sensible. Ditto the lockout switch so it would only operate in 4th gear to prevent ditzy owners using 1st or reverse with the overdrive and burning it up. Good idea.
However, the third contraption was overly complex and pointless. On the carburettor throttle shaft, there was a cam with two micro switches that would drop the overdrive in and out when the engine speed was too low. I could never figure out the purpose of this, as the overdrive kickdown switch would surely do the same thing. This was to prevent you from lugging the engine with the overdrive and stressing everything, but again- if you floored it in overdrive, you’d depress the kickdown button. When it was new, I’m sure this made the drive buttery smooth- that bit of overkill just to get the car to be that little bit more refined. Unfortunately, after a few miles and decades, the effect was exactly the opposite.
As the brass bushing on the throttle shaft wore, the cam would flop about temporarily disconnecting the switches and making the overdrive switch on and off every few seconds. My p4 guru bypassed it and said that even he had no idea why the thing existed, as it served no practical purpose.
Moreover, my ’79 Volvo uses the same (well actually the J type not the D type) Laycock overdrive. It doesn’t have any kickdown switches or funny sensors, but just a 4th gear lockout and a little button to shift in and out. Volvo kept with their trusty Laycock until the mid 90s on the euro market 900 series. Is the Volvo brick the last passenger car with an overdrive? I can’t think of any others.
For 2 lane highways, overdrives are much better than a 5th gear, simply because you don’t need to clutch and physically move the lever, but just flip a switch to pass, meaning you lose fewer revs downshifting. Whats more, when 4 speed gearboxes had 5th gears added in the 80s, they were found to make the gearbox less reliable- Volvo M47, Saab 900, Lada Niva, are some examples of very robust 4 speed boxes that became failure prone due to the extra idler shaft being crammed in at the top and not getting enough oil.
I’m pretty sure that Volvo was the only non- British car to use that style OD. My theory was that it was a purchasing bundle with the SU carbs – maybe the same sales rep handled both lines – and persisted even after Volvo switched to fuel injection.
IIRC, both Ferrari and Maserati offered the Laylock electric OD in the early 60s. The Wikipedia entry says “Several famous marques used A-type overdrives, including Jaguar, Aston Martin, Ferrari, Austin-Healey, Jensen, Bristol, AC, Armstrong Siddeley and Triumph’s TR sports car range, until the end of TR5 & TR250 production in 1969.” Maybe I’m wrong about Maserati.
Update: Some quick Googling indicates that the 3500GT went from a 4sp ZF to a 5sp ZF in 1961, so apparently no Laylock OD.
Great, now where is the history for the Laycock de Normanville overdrive system?
In the mid-90s I had a ’64 Rambler Ambassador 990H hardtop with the AMC “Twin Stick” which was a 3-speed manual + OD. Mine never worked, though, as the 327 V8 engine would die when I applied the overdrive lever. It ran fine with just the three speeds anyway, though I’ve read that it could be used to equate a 5-speed if it had worked.
I think Volvo was the last car maker to offer an overdrive unit.
I have two of ’em. One from a 63 Fairlane (with the five bolt bellhousing pattern) that I found oddly in the trunk of a 76 4dr Maverick parts car, and one from a 67 Galaxie (with the 6 bolt bellhousng pattern). Still trying to figure out what I want to put them in. They are both R10 Overdrives behind T86 tranny’s. I only have two stick shift cars, a 71 Maverick and a 75 4dr Comet (that was one of only 388 made with 200/stick). And the Comet was a customer order that sat for almost one year, meaning the customer must have backed out. Bet the dealer was pissed, what with a stripper sedan that no one wanted. Well, the Comet does have AC. Buts that’s almost all. Even still has four wheel drum brakes and manual steering (5.2 turns lock to lock baby!!).
I read somewhere to get the most from an interstellar overdrive you have set the controls for the heart of the sun.
Inadvisable when you’re learning to fly though.
I’ve always had better luck with the Infinite Improbability Drive although the unit itself is unpredictable. 😉
I currently have a GM three speed overdrive a friend gave me that he took out of a corvette powered old drug running van when I was installing a new clutch in my 56 Chevy pickup back in 1984. My pickup had a 283 single hump heads with a 4 barrel, and the way we installed it I run first gear as normal , and hit the overdrive button which shifts it into first gear overdrive – wind it out then shift to second gear conventional and so forth thru the rest of third gear so actually it is like having a six speed with the great advantage of free wheeling. I have gone cross country many times hauling my 52 Harley flathead trike in the back. Great gas mileage and a VERY sweet road gear.
I find that first gear overdrive is too close to second straight to bother with in normal driving, but I do use it sometimes when I don’t want to shaft before another stop sign or such.
I am surprised in all this discussion, there is no mention of the Doug Nash 4+3 (OD on 2, 3, and 4) unit in the early C4 Corvette. Car and Driver described it as a “transmission smarter than your average driver”. It was an attempt to get a five speed into the Corvette when the T5 wasn’t strong enough to survive behind a 350.
It is interesting that the BW unit freewheeled in direct. The Gear Vendors unit has very strict instructions to not overrun the unit in OD, as it will burn up the unit. A freewheeling clutch would prevent this.
This sounds like the opposite to the BW – what is the purpose of the freewheel clutch? Is it there to protect the OD or is it just to ease shifting?
It may be intrinsic to the design, or maybe because it eliminated clutching, which was seen as desirable.
Several car manufacturers had various methods which were supposed to make it unnecessary to use the clutch. Most did not work very well. Packard had the vacumatic clutch. Hudson and some other contrivance. Nash had the E-stick. Even VW had something.
The VW beetle semi-automatic transmission had a switch which would disengage the clutch when you touched the gearshift. The gear box itself was like the normal 4-speed except that 1st was disabled. In addition, there was a torque converter.
Mercedes also has something to make it unnecessary to use the manual clutch. None of those systems were very good and didn’t stay around for long.
The VW “auto stick” was a variation on the 1950’s Saxomat with the additon of the torque converter instead of first gear.
That’s interesting new information.
I did a google search on Saxomat and found that it was used on several cars.
Armstrong Siddeley had a thing called a manumatic where the clutch worked by touching the gear lever Ive seen one in a 234 sedan, it looked like it would give trouble.
Well, I think it’s partly a matter of mechanical simplicity. To obtain a simple planetary overdrive, where the planet carrier is driving (connected to the transmission output shaft), either the sun gear or the ring gear is held, and the other drives the tail shaft. If you want the overdrive to be a part-time unit, where the driver can decide when it operates and when it doesn’t, you need two things: (a) some way to selectively get direct drive (everything turns at transmission speed) and (b) some way to selectively hold whichever element is held to provide overdrive.
Now, depending on how the pieces are arranged, there are various ways to do that, including drum brakes (expanding or contracting), disc brakes (single or multi-disc), and freewheeling clutches. However, a disc or drum brake requires some kind of positive control mechanism, like a hydraulic servo or a centrifugal governor, which costs additional money, takes up space, and adds weight. A freewheeling clutch doesn’t — it will lock when there’s torque on it in the “wrong” direction and unlock when there’s not. So, if you use an overrunning clutch for one of those two duties, you can get away with having only one positive control system and leave the other one to its own devices.
Very nice article. Didn’t realize the OD transmission was that versatile and convienient, i.e., a semi-automatic transmission at town speeds by leaving it in second and allowing the unit to shift into OD or forced shifting back to direct 2nd by mashing down on the accelerator pedal (a la automatic transmission) for added power and acceleration.
I still have pie-in-the-sky dreams of finding a 1953 Chevrolet 210 with a three-speed manual and stovebolt six like the one my dad used to own. After reading your article, I realize it would be nicer to have that BW OD unit instead of the standard conventional three-speed unit. The BW OD also sounds more versatile than the Powerglide automatic transmisison.
Is it possible to add-on the BW OD unit (if it can still be found) to the conventional three-speed manual?
In 1968 my dad bought a 1/2-ton long bed GMC pickup equipped with a 292 inline 6 and 4-speed manual (1st gear granny). Wish I still had that truck. I recall reading in the operator’s manual a brief discussion on the operation of the optional three-speed manual with overdrive that operates just as described in the article above, i.e, to engage the overdrive a handle is pushed in. The unit shifts to overdrive when the speed is over 30 mph and the foot on the acceleration pedal momentarily lifted. With the handle pulled out, the transmission operates as a conventional three-speed unit.
I wished that four-speed manual had the OD provision as described for the three-speed. At freeway speeds the engine sounded quite busy, despite having a 3:54 rear axle.
One aspect of operation not mentioned (or I may have missed it) in your aticle is when you intentionally want to lock out the overdrive above 30 mph, i.e., when driving in hilly terrain or pulling a trailer. As I recall from the manual, you mash down on the acceleration pedal and pull the handle out simultaneously.
Again, a very nice article.
Thanks,
You can’t get or add OD to a pre-1955 Chevy, because they have a torque tube drive shaft, which makes it essentially impossible to add OD. That’s why Chevy didn’t offer OD until 1955.
Yes, unfortunately, the OD units don’t readily fit the four-speed boxes, like that in your dad’s truck. It’s a trade-off: a granny low gear, or an OD gear, but not both!
Ramblers with torque-tube drive had overdrive available from the factory. Of course to add it to an existing car you’d need probably need to transplant not just the overdrive unit but the entire torque-tube/rear axle setup.
Chevrolet asserted that because their engines were loafing on the highway they didn’t need OD. I didn’t agree. I learned to drive with my mother’s 1950 Chevy with manual transmission. The engine was quite noisy on the highway and to me it didn’t seem to be loafing.
When my father bought his 1951 Nash Rambler I wanted him to get it with OD. He said that with OD the rear axle ratio would be lower which would cause it to use more gas in city driving where you couldn’t use the OD. So, he got it without OD.
His father at one time had a 1914 Cadillac with a 2-speed rear axle controlled by the driver’s right hand with a switch on the door. Until 1915 the Cadillac was right hand drive like many other American cars. The reason for the 2-speed rear axle was to reduce the vibration of the 4 cylinder engine when driving on the highway. So, the concept of an OD or 2-speed rear axle was not exactly new when BW introduced their OD.
I installed a BW free wheeling overdrive in my 56 Chevy pickup after a friend gave it to me out of his 72 corvette powered former drug running van.
I had a 283 four barrel single hump head motor.
The way i set it up is three speed on the tree – wind first gear out, hit the overdrive button which shifts into first gear overdrive , wind it out then hit the button and shift into conventional second gear and follow suit with third – in actuality it is a six speed. With thirty percent less RPM’S in overdrive gas mileage is best and a quiet road trip truck is enjoyed. I have traveled the eastern seaboard hauling my 52 HD flathead in the back.
Only downside is freewheeling in the mountains and hard on brakes, but the manual lever takes it in and out of free wheeling.
I suggest no using the OD in first gear. It is not designed to take the torque multiplied by the first gear ratio. I suggest using it only in second and high.
How could you forget about Packard?
I know that the BW overdrive was available on some 1940 Packards but it might have been available even before then. It was available on Packards until the last Packard was made in 1956.
Willys, Kaiser, and Frazer also made the BW overdrive available. It may be that only GM never had the BW overdrive available until Chevrolet finally made it available in 1955.
Actually, I think that a 4-speed transmission would have been better but American drivers saw 3-speed transmissions as correct and did not want to drive with 4-speed transmissions which is why the BW overdrive was invented. The OD was a bit kludgy in that it freewheeled below about 28 mph unless you locked it out and the freewheeling was annoying. I owned a 1951 Ford V8 with overdrive.
My father had a 1953 Austin Healey with the Laycock de Normanville overdrive but that was completely different from the VW overdrive. It could be shifted under power and when shifting into overdrive it sounded like an automatic transmission upshifting. Under no circumstances did it have freewheeling. It was better than the BW overdrive. It was available on several English cars and the Swedish Volvo. The GearVender’s overdrive was patterned after it.
Packard first offered overdrive in 1937.
I know these older OD units existed but my only experience with one was in an old Volvo 240 wagon that I bought to tinker on. I never did get the shifter mounted button to work.
Anyway, I’m now looking for another transmission to replace the broken 3-speed column shift on my slant six Belvedere. So far, I’ve been on the lookout for a 4-speed slant six manual but have had surprisingly bad luck finding one. I can find the same 3-speed all day long. It makes me wonder if there are any 3-speed with OD units that I can use in my Plymouth.
Paul, where did you find that postcard of Hopkinsville, KY? I was there last month for three weeks on business and recognized that scene before I even saw the writing–many of those buildings are still standing (including the ones at far right with the very distinctive pointed arch windows on the third floor). But it’s not a very well-known place.
Also a very detailed article–I knew nothing about these older overdrive systems; now I feel quite well-educated on them! The ability to substantially reduce the use of the clutch seems quite appealing, especially in town, and combined with lower freeway RPMs gives you a dual benefit.
On the web, like pretty much everything else that I don’t have my own pictures for. 🙂
I probably Googled “street scene 1930s” or something like that.
It’s a postcard (not watermarked, etc.) for sale on eBay right now:
http://www.ebay.com/itm/HOPKINSVILLE-Kentucky-KY-MAIN-STREET-SCENE-20s-Cars-c1920s-Postcard-/291702468059
Since this was first published, I have come to know that one of the most ardent suppliers of BW OD was Studebaker. From what I have read, it is not that common to find a 3 speed Stude that does not have it. It was a popular option for Bakers, both V8 and stick, all the way to the end of American production. I suspect that it may have been there in the Canadian cars as well.
I think it was this OD unit that allowed the little Champion 170 CID flathead six live as long of a life as it did (through 1960) and to still be decent to drive in most conditions.
To the best of my knowledge, the last car to use the LdN overdrive was the 1992 Volvo 740 Turbo. Although Volvo had morphed the basic 4-speed ‘box (the M45) into a true 5-speed (M47) transmission by 1987, that true 5-speed trans was not strong enough to hold up to the higher output of the Turbo, so the 740T models continued to use the M46 (4+OD) box until the model was discontinued in 1992.
I had a next door neighbor who had a 1969 Volvo with OD. I had assumed that it was the LdN OD, but from what one poster wrote here, it could have been made by another company. However, it’s operation was like the LdN OD.
As far as I know, any Volvo with an overdrive had a LdN unit. Volvo used several different models of o/d unit, but only that brand.
I’m olde enough to remember when the Borg Warner overdrive was an option on practically all cars except GM cars. Chevrolet didn’t offer it until 1955.
I see the BW overdrive as a kludge; the English Laycock de Normanville OD was far better. My father’s 1953 Austin Healey had it. It was also available on the Jaguar, Volvo, and some other cars.
Many people, including people who owned cars with the BW overdrive, did not know how to use it. Once I rode with someone whose Chevy station wagon had it. He’d start driving and the first time he happened to take his foot off of the gas, it would shift into OD. Then, on some hills, the car would actually lose speed because he didn’t know that you have to push the gas hard down to the floor to make the OD drop out.
I rode with an industrial arts teacher whose Studebaker had OD. When reaching the city limits to drive out of town, he’d stop the car before pushing the OD lever in to make the OD available.
A friend of my mother had a 1955 Ford Thunderbird with OD. The speedometer failed and she wanted my father to drive his car at 60 mph so she could follow and see what the tachometer indicated at 60 mph. Then, in driving with my mother, she’d get up to 60 mph but the first time she took her foot of the gas, it would shift into OD. Then, when she stepped on the gas again she couldn’t figure out why she was passing everyone! Of course in OD the car speed would be about 30% higher for the same tachometer indication.
A mechanic told me about a driver who accidentally discovered the full throttle kick down. He said that as he was going up hill, suddenly something broke loose, the engine sped up, and the car began to pick up speed quickly. The driver had owned the car for several years without becoming aware of how the OD worked.
One would think that a driver would notice that when he took his foot off of the gas it would shift into ID; the change in engine speed and reduction in power should have been obvious. However, many drivers never noticed it.
Perhaps others also have stories about people who didn’t know how to use the BW overdrive.
Thanks for your comment. I’m not surprised about the general lack of knowledge on its use. By the 50s, Americans were used to either three speed manuals or automatics. The B-W OD requires a certain level of engagement to use properly.
Frankly, even I didn’t use mine fully until I read an article on it. I would only activate it and engage it when I got on the freeway/highway, and on third only. I was nervous about the freewheeling, given the mediocre drum brakes on my truck.
Learning how to use its full potential was an eye-opener, and now I use it all the time. If I’m going down grade, I make sure I’m either in 2nd-OD, or disengage the OD if I’m in 3-Direct, to avoid the freewheeling. That’s become second nature now.
But it all must sound rather arcane to someone who is not really interested in using it. It’s not for the disengaged driver. 🙂
Seems to me that the problem was the automatic centrifugal switch behind the manual transmission. If they had either put a toggle switch on the dash (as you and many others have done) in the first place, or developed a unified gear selector so that 2-OD, 3-direct and 3-OD presented as third, fourth and fifth respectively the problems would’ve been solved.
I had a 1951 Ford V8 with the BW OD. I bypassed the centrifugal switch and controlled the OD with a switch on the dashboard. My usual sequence was to start in 1st, shift to 2nd, then to 2nd OD. There is advice not to bypass the centrifugal switch since attempting to back up with a manual switch “on” could damage the OD unit. That’s good advice for people who might fail to turn the manual switch to “off” before stopping the car, but for most of us there should be no problem.
The freewheeling makes it easy to shift to 1st without double clutching when the car is still moving. To do that, either the car should be below the speed at with the OD will engage or, if you have a manual switch, it should be “off”. That is to ensure that the OD will be in freewheeling. Then, while in 2nd gear, ensure that the car is under power. Next, close the throttle and INSTANTLY and QUICKLY shift to 1st. The shift will be completely quiet.
The only advantage of the freewheeling is that it permitted shifting without the clutch, provided you knew how to do it. However, I did not like the freewheeling at all. It made engine braking impossible while freewheeling. Also, after coasting, when you stepped on the gas, there was a lag while the engine sped up and a jerk when after the lag the engine started driving the car.
My dad ordered his ’65 Checker with the 230 ci 6 and three-speed manual transmission with overdrive.
It was my car to drive by the time I was in HS. I don’t recall ever using the overdrive in anything but high gear (never in 1st or second). I remember pressing the gas pedal to kick it out when needed.
I swapped a gearbox with the Laycock de Normanville OD into my 1970 MGB and it was wonderful! The car was so much more pleasant at highway speeds. I think Corporal Klegg had one in his….
My dad’s 1980 Supra had an odd OD arrangement. In order to quickly offer a four speed overdrive automatic transmission, they added a separate OD unit behind the three speed automatic. It was engaged like the Volvo units I had driven, with a pull switch on the dash.
J.C. Whitney used to offer a kit to add the BW OD to automatic transmissions. How successful it was I have no idea.
Except for the GM 4-speed Hydramatic which used 3 planetary gearsets, at least one of the first American 4-speed automatic transmissions was made by putting a 2-speed overdrive gearset between the torque converter and a 3-speed planetary gearset. With split shifting that would have resulted in 6 speeds but the way it was made they got only 4 speeds because the OD gearset did not shift into OD except when the 3 speed gearset was in direct drive.
That arrangement made a lot of sense because the OD gearset did not have to handle the torque of the engine multiplied by the low gear ratio of the 3-speed gearset.
It is interesting how long it took for mfgs to use their Automatic OD transmissions as 3×2 and make the full 6 speeds available. The transition started with 5sp versions some of which acted like a 4sp most of the time. The normal up shift followed the traditional 1st, 2nd, 3rd and then 3rd OD. However they programed it to have a true “passing gear” by downshifting to 2nd OD in certain situations. Then came full time 5sp with a 1st, 2nd, 2nd OD, 3rd, 3rd OD up shift schedule. They quickly starting using the full 6sps available from that 3 + OD.
Some 6-speed automatics now don’t get their 6 speeds by combining a 2-speed planetary gearset with a 3-speed planetary gearset. I saw a diagram of a Honda 6-speed automatic which did not use that method. The gear arrangement looked so bizarre that I could’t understand how much of it worked. If I correctly recall, for 1st gear it drove a sun gear which was meshed with an inner set of planetary gears which was meshed with an outer set of planetary gears (both sets of planetary gears being on the same planetary carrier) which was meshed with an internal gear.
Mr. Howard Simpson, knowing that he had a fatal disease and didn’t have long to live, invented and patented a number of planetary gear sets so that his family could live on the patent royalties therefrom. It seems that for some time car manufactures have been using his gear sets. He was a true genius.
A compound planetary gearset like you describe is typically called a Ravigneaux gearset, although Pol Ravigneaux patented a bunch of variations. Several early automatics used two-speed Ravigneaux gearsets, including Dynaflow, Powerglide, and the ’60s Super Turbine 300/Jetaway.
Probably that also includes the Ultramatic.
I wasn’t sure off the top of my head, but yes, Packard Ultramatic did as well.
As a Volvo dealer tech in the 80’s, I saw many Laycock overdrives. They were wired through a switch that only allowed engagement in 4th gear. Every now and then, an enterprising owner would wire around the switch. They were fairly reliable units. More often the issues were wires breaking in the shifter or in the later models, sticky relays. Later in the 80’s, they were replaced with actual 5-speed boxes.
As a kid, the family ride was a 66 Ford Custom 500. 289 with 3spd and OD. Many years later, I remember my Dad commenting on the non-synchro first gear. It was sold off a few years before I learned to drive.
When synchromesh was introduced, on American cars with 3-speed gearboxes, only 2nd and 3rd were synchronized. One explanation I read was that if 1st were synchronized, it would be too hard to shift into 1st when the car was standing still unless the driver shifted to 1st quickly after declutching. Whether that was the real reason I don’t know. However, the 1967 Chevy II had synchronized 1st and I believe that some other American cars did too, and before that.
Drivers were generally advised to stop before shifting to 1st. However, my father, who was born in 1899, learned to drive before synchromesh was invented. He told me how to double clutch to shift to 1st when the car was moving. That was not difficult to do, but most drivers never learned how to do it. Actually, by double clutching all the downshifts, the life of the synchronizers can be extended.
On some cars, the synchronizers were prone to failure. I remember a friend’s 1953 Kaiser Manhattan on which the synchromesh had failed. I had to teach them how to double clutch. My father’s 1953 Austin Healey had synchromesh on 1st but the synchromesh was so weak that it was faster to double clutch into 1st than than to shift gently and wait for the synchronizer to work.
Because I’ve had transmissions on the brain, I feel obliged to point out that Hydra-Matic was not introduced until the 1940 model year (which began in late 1939, if you want to be particular). Hydra-Matic’s predecessor, the semiautomatic Automatic Safety Transmission, was first available in 1937 and was offered on Oldsmobiles pretty much until Hydra-Matic debuted. (Buick used the transmission in 1938 only.) A minor point, but if you’re in an updating mood, it bears noting.
Incidentally, the freewheeling-in-direct issue was the reason a look at cross-sections of the second- and third-generation Hydra-Matics, which both used overrunning clutches, reveals additional “overrun bands” and “overrun clutches.” They didn’t work in normal Drive range, but would be used in the lower ranges for descending hills without running out of brakes. (The original Hydra-Matic didn’t use freewheeling clutches and didn’t need separate overrun brakes.)
Paul, I’ll admit I didn’t read every comment above, so sorry for any “repeats.”
AMC’s brochures say their ’75s and ’76s (including the Pacer) can have 3-speed with (optional) Overdrive; it’s not in the ’77 brochure.
Chrysler (mid-1970s) has an “Overdrive-4” transmission, but that’s just a 1:1 third gear and 0.73 fourth; available into the 1980s, evidently. There’s a nice ad that brags about the highway mileage the D-100/Slant Six with this gearbox:
Interesting, about AMC’s offering Overdrive in ’75 and ’76, on all models except the large ones. It was clearly in response to the energy crisis, but there probably weren’t many takers. Until someone can show otherwise, I’d say confidently that this was the Overdrive’s last hurrah.
I’ve updated the text. Thanks.
Great article, years ago I owned a ’64 Chev 8ft step half ton with the 230 and overdrive. It was a great truck to drive and would touch 20 MPG. Truck was totaled, but the trans and OD are in the shed. Currently I am considering a Gear Vendors for a Dodge Sweptline with a 383 and Torqueflight. A friend sold me 3 busted GV units cheap, they are actuated hydraulically vs a solenoid operating a band on the BW.
Isn’t the BorgWarner a pawl rather than a band? (That’s what the diagram above indicates, although I’m not familiar enough with the innards to know if there are variations on different units.)
Yes. The BorgWarner uses a solenoid which actuates the pawl through a spring. The pawl engages a notched disc which is connected to, or part of, the sun gear. A balk ring keeps the pawl from attempting to engage the notched disk until the sun gear turns backward slightly when the engine slows down to OD speed after the driver closes the throttle. At that time, the pawl engages the notched disc and the car is in OD.
What can cause blinking of overdrive light in ford explorer?
And I need a diagram displaying where O/D fault can be located.
I posted this in the wrong place at first.
I had four cars with OD but only two of them worked. The +/- 25% OD attached to the rear of the Spicer (Dana) T18 transfer case was a virtual necessity. With 5.38:1 gearing, even with 16″ tires, 55mph was a struggle in direct drive. The system was mechanical, only worked in 2WD and a version of it is still being offered.
#2 was a bit more exotic; an electric OD in an Austin-Healey 100-4. The on/off switch was on the dash and the in/out toggle was on the shifter., so 1-2-2OD-3-3OD was rapid and smooth… until the famous English electrical system went south for the winter.
#3 and 4 were a ’53 Ford Customline and a ’47 Studebaker Champion, both 2 door models. Neither had a working OD. I wanted to fix the OD but was talked out of it for three reasons: 1) fixing would be too expensive. How someone could know that without diagnosing the problem is beyond me now, but then I was just a trusting kid. 2) OD systems were unreliable and the fact that these were inop was proof of that. 3) “experts” told me that the OD systems were weak due to the planetary gearset and that was probably the cause of the OD units to be inop. So, both cars went off still with non-working OD and I never got the chance to see what was wrong or how well they operated.
I still don’t know about the alleged lack of strength. Since I like to tow things that could be an issue but probably one I won’t have a chance to face.
Back in the fifties, my father drove a 25th series Packard Standard Touring Sedan with OD. Great gas mileage from the smaller straight 8. Drove around in style on the cheap! He added 3 “bottle openers” on each side and if I remember correctly, the whitewalls were double sided. About 12 years later, I owned a Lark V-8 with the B-W OD. Quite a sleeper when the light changed with the 4.11 Twin-Traction! Be careful though that “free-wheeling” means just that. The going downhill experience could be thrilling. Fortunately, the Lark had better brakes then most cars had back then.
I put a Borg-Warner overdrive (OD) behind my 390 engine in my 1964 Ford Custom sedan. I did not want to have to kick the accelerator down to the floor, to get out of OD, so I added a “parallel” wired switch to my dash, so when the engine started to lug down going uphill, I pushed the button and was immediately into third gear direct. Saved both gas and wear and tear on the transmission. Like others have mentioned above, you could leave the OD lever in and have freewheeling around town, when driving below the governor kick in speed. And when below overdrive shift speed, you could get out of freewheeling while gently accelerating and, at the same time pulling the lever out. Lots of fun to drive – as long as you remembered to take it out of OD when you parked it.
Why was a control that was used so often put in such an awkward place? It seems the overdrive switch should be on a dashboard pod near the steering wheel, on a stalk, or on the steering wheel itself like the popular up/downshift buttons common today. Not way down on the knee bolster like the parking brake release.
(p.s. – thanks for the Interstellar Overdrive link; listening to Syd Barrett-era Pink Floyd always makes for a better day)
The control was not intended to be used often. There was a widespread idea that the overdrive should be locked out for city driving and that it was for highway driving only. Also, damage could occur if the position of the control was changed under the wrong conditions. Having it under the dashboard reduced that likelihood.
Pushing the control in enabled the OD to operate; pulling it out locked it out. The position could be changed when the vehicle is standing still. For the position to be changed with the vehicle moving, the vehicle should be under power with the OD not engaged, i.e., below the speed at which the centrifugal switch would supply power to the OD solenoid. Or, if above that speed, if the OD ratio is in effect, the accelerator should be completely floored to cause the OD solenoid to drop out thereby disengaging the OD then, while the vehicle is still under power, the OD control can be pulled out to lock out the OD.
The above was apparently too complicated for some people; they always stopped the vehicle before changing the control position. Some drivers didn’t even know to release the accelerator to get into OD or to floor the accelerator to cause the OD to drop out. They would get going on the highway and the first time they had to release the accelerator to slow down the OD would engage. With the vehicle in OD, if they had trouble ascending a hill, they did not know to floor the accelerator to cause the OD to drop out.
Actually, the OD was a kludge invented because American drivers would not shift a 4-speed transmission properly. Instead, they would use it like a 3-speed transmission and complain about sluggish acceleration. The OD was intended to provide the advantage of a 4-speed transmission to drivers who would not properly operate a 4-speed transmission.
You’ve pointed out quite correctly that with time, fewer and fewer drivers understood how overdrive really worked and how it should be used properly. The many comments to my Youtube video make that clear; but then it’s been a long time since overdrive was common.
I’m not sure I agree with you about it being invented because Americans complained about sluggish acceleration from the three speed. In reality, drivers invariably would shift from 2-OD into 3-OD, which was quite a big gap, and did nothing to improve acceleration. That’s why I have mine set up manually, to always shift from 2-OD to 3-Direct, then 3-OD. That’s the equivalent of a five speed, since 1-D and 2-D are used too.
Who are the “drivers that would not properly operate a 4-speed transmission properly”? First, there were no four speeds available during much of the OD’s heyday (1946-1968 or so). The first four speeds for passenger cars started in 1959, and then only on very few models. Plus, four speeds did nothing to reduce engine speeds on the highway. Four speeds were strictly oriented to those seeking maximum performance; that was not the target market for OD.
There were also some truck-style passenger car four-speeds before the war, which were basically the opposite of overdrive: a three-speed transmission with an extra-low bottom gear. They weren’t terribly useful in an American context (with a big-displacement six or eight, people could and did just start in second) and so they were mostly gone by WW2.
Of course, some postwar English and European cars had loosely similar four-speeds with very steep low gears to make up for limited low-end torque (like the English Ford four-speed also offered on the early Falcon and Mustang six, which had ratios of 3.16/2.21/1.40/1.00)
I’m aware of those. It was something of a fad; a marketing thing. Functionally, they were pretty useless, in terms of the extra gear, given the power curve and typical speeds of the time.
Paul, my frame of reference begins before 1930 when several American cars did have 4-speed transmissions. Check out this article:
https://www.hemmings.com/stories/article/four-speeds-of-the-30s
Production of 4-speed transmissions was stopped in about 1930 because people AT THAT TIME insisted on starting in 2nd gear then complained about sluggish performance. The situation from the middle 1940s until the late 1950s was very different.
It is true that for one period of time 4-speed transmissions were aimed at the performance crowd whereas ODs were aimed at the economy crowd. 4-speed transmissions were available only with V8 engines which actually needed them less than 6 cylinder engines. I remember being told by one car salesman that there would be no point in having a 4-speed transmission with a 6 cylinder engine. Of course most car salesmen didn’t know much about technical details and physics.
With 3-speed transmissions, TYPICALLY the step from 1 to 2 was much smaller than the step from 2 to 3, partly because 1st gear was not synchronized and most drivers thought that you could not shift to 1st with the car moving; few knew how to double-clutch. So, they depended on a 2nd gear with good pulling power from very low speeds.
OD equipped cars generally had a somewhat lower rear axel ratio than cars without OD. So, in addition to improving fuel efficiency, OD also improved performance. Thus, when people bought a car with OD to improve fuel efficiency (and make cruising quieter), they also got better performance although that fact was not generally used as a selling point for OD. When Fords were equipped with OD they actually had a closer ratio gearbox too.
The BW OD had a ratio of about 0.7, the reciprocal of which was 1.43. On most cars the step between 2nd and 3rd was TYPICALLY much greater than 1.43 so in 2ndOD the engine speed was typically higher than it was in 3rd. That was certainly true with my first car, a 1951 Ford V8 with OD which I bought in 1958.
I learned to drive with my mother’s 1950 Chevrolet. 2nd gear was good for only about 40 mph and the engine speed was cut about in half when shifting from 2nd to 3rd.
Yes, I’m familiar with those early 4 speeds. I’ve read that article. And I see your points.
The prewar four-speeds suffered from not having an optimal starting gear for general use. On the Packard Eight, for instance, first on the four-speed was 3.13, which was too short with a 385 cubic inch engine, and second was 1.85:1, which was too tall; also, only third and fourth were synchronized. So, switching to a three-speed with a low gear between those ratios was a better compromise for performance except in certain unusual circumstances (like maybe starting on a steep hill).
The impact of gearing on performance is complicated. Road & Track in the late fifties tested a couple of Chevrolet V-8 cars with different transmission choices and found that the regular three-speed with 3.70 axle provided better acceleration and (if I recall correctly) a higher top speed than an overdrive car with a 4.11 because the shorter axle ratio forced earlier shifts to second and third, which hurt acceleration more than the added multiplication of the shorter axle ratio helped. In top speed, the 4.11 axle reduced top speed in direct third, but overdrive third (at 2.88:1) was too tall to overcome drag at the top end. Of course, real-world performance is not necessarily reducible to this kind of track testing, and it’s easy to see lots of places where the 4.11/overdrive combination would be a better real-world compromise than the non-overdrive 3.70 (especially in terms of fuel economy), but it is still a compromise either way.
Akismet continues to eat far more of my comments than it publishes, but Road & Track in 1956 or ’57 tested Chevrolet V-8s with both the standard three-speed 3.70 and the overdrive 4.11, which found that the overdrive actually HURT both acceleration and top speed. Basically, the shorter axle ratio reduced maximum usable speed in each of the direct drive gears, which hurt more than the added multiplication helped. On top, the 4.11 axle reduced top speed in direct drive, while overdrive third (at only 2.88:1) was too tall to pull very hard above 90 mph. In the real world, overdrive had advantages in some situations (and in fuel economy), but in terms of measured performance, it really didn’t help.
I would love to try driving this and experience it. I’m used to a two-speed rear axle on grain trucks, having had to drive them as a kid on my parents farm in the 90s, and they operate somewhat similarly from a driver’s perspective, but no freewheeling. The actual mechanism is totally different though. Maybe I should do an article on that.
My family’s 1955 Chevy wagon had OD, so did Dad’s Jeep station wagon. The speed sensing engagement control on the Chevy quit early on, so Pop put a toggle switch on the column mounted shift lever, which allowed all sorts of gear ratios and enabled a hill holding device.
With the OD engaged the car will not roll backwards as the one way clutch comes into play.
So the plan was to stop with the OD engaged, let the car roll gently backwards to lock up the OD unit, then switch off the OD. Tension within the OD unit kept it engaged, but as soon as the car moved forward, the OD would disengage and car drove off in first gear.
Some years later the ol’ 55 was sold to a local hot rodder and replaced with a new 1967 Chevy 6 wagon with OD. The speed switch worked on this car, annoyingly engaging the OD at around 35 mph, which was far too slow. I was driving my own cars by this time so didn’t really care.
I did own a Volvo 265 wagon with the OD switch right in the knob of the floor mounted shifter. That OD was the Laycock version, a different animal.
When I had my 1951 Ford V8 with OD, I also discovered that hill holding trick. With the manual toggle switch to replace the centrifugal switch, it was even possible to engage the OD in 1st gear but of course that would have put more strain on the OD so probably would not have been a good idea.
I understand the post which correctly asserts that at least some Chevrolets performed better when not equipped with OD. The problem, I believe, was that the 3-speed gearbox had the same ratios whether the car was equipped with OD or not and, because OD equipped cars had a lower differential ratio, 1st gear was really too low. On the other hand, on OD equipped cars, Fords had a 3-speed gear box with closer ratios so I doubt that that problem would have occurred with Fords. Probably both were over-geared for economy in OD which could very well reduce the top speed.
Regarding owners’ not understanding how to use the OD, I have stories.
Once I was riding with a couple guys in a Chevy V8 station wagon with OD. It was obvious that the owner did not know how to use the OD. When starting out, he would shift normally but never release the fortissimo pedal to allow the OD to engage. Then, the first time he had to slow down a bit and released the fortissimo pedal, the OD engaged. On a hill the engine was knocking but he did not understand that he had to floor the gas to cause the OD to drop out. On the other hand, when his passenger took over driving, it was obvious that he knew exactly how the OD worked. One would think that an observant driver would notice the difference in sound and performance when the OD engaged, but many did not.
Decades ago a widow friend (Helen) of the family was visiting us. She had a 1956 Ford Thunderbird with OD. Although it had a tachometer she never used it, until the speedometer broke. Then she had my father drive his Austin Healey (with Laycock de Normanville OD) at 60 mph so she could see what the engine speed was at 60 mph until she had the speedometer fixed. Well, she and my mother embarked on a 200 mile trip. Helen got up to 60 mph by using the tach but then, when she released the accelerator, the OD engaged. Later, she said to Mum, “I’m having trouble maintaining 60 mph; it seems so fast and I’m passing everyone.”.
Then there was the man who told his mechanic that usually his car barely made it up a hill but just recently something broke loose, the engine revved up, and the car zoomed up the hill. Apparently he had no idea how the OD worked and for the first time he accidentally kicked it out of OD by flooring the accelerator.
Probably most of us have trouble understanding how some drivers can be so unobservant and unaware.
It’s 10:00 AM in Valley Cottage, NY. i have no time to read this now so I formatted to size 12 font, right and left justified and moved everything to not be indented. T result is 56 pages for me to read in the car. I have placed the essay in a booklet. This looks like super information to enjoy. Thanks to you all from 2012 through today! Tom
My family had a 1968 Checker with the Chevy 230 6, 3-speed and overdrive. 30 mpg was achievable on the highway with this big heavy car using the OD.
How is the cost comparison between a standard 3 speed, a 4 speed and a 3 speed with overdrive? Mechanical efficiency? I would think that a 4 speed or 5 speed with the correct ratios would be mechanically more efficient than a 3 or 4 speed plus OD. How about weight? Great article. Thank you for writing it and for all the learned comments.
On the 1965 AMC Ambassador, which offered all three combinations, the three-speed with overdrive listed for $115.00, the same setup with Twin-Stick console shifters $147.50, and four-speed (a late ’65 introduction) for $188.10.
The Ambassador V-8 had the Warner Gear T-86, which when combined with overdrive had 2.49/1.89/1.00 gears. According to this link — https://www.amccf.com/tech/amc_manual_trannies.html — AMC used 2.43/1.76/1.46/1.00 gears in the Warner T-10 four-speed. So, for a given axle ratio, starting ratio was very similar, but the three-speed had a shorter second gear and an additional 1.30:1 intermediate in 2nd-OD. Even with a shorter axle ratio (AMC specified 3.54:1 with Twin-Stick OD), the three-speed OD would always have a taller top gear with OD engaged; the lowest numerical ratio AMC offered was 2.87:1, while OD with a 3.54 axle would give a final drive of about 2.48:1.
On the other hand, the T-10 had a synchronized low gear, which the three-speed did not, and Motor Trend complained that the three-speed/OD transmission would not allow fast shifts at all, plus the additional delay of engaging or disengaging overdrive. Also, Motor Trend found top speed in 3rd-OD was lower than in direct third, so it looks like even with the 327, the overdrive was too tall to pull more than 100 mph. So, the OD provided an advantage in cruising economy, but not in performance.
I can’t find comparable weight figures, but I’m pretty sure a T-10, even with an iron case, was lighter than the T-89 three-speed with overdrive.