(first posted 9/23/2014) Chevrolet’s two-speed Powerglide automatic had a long career, and a somewhat strange one at times, especially so in its relationship with the Corvette. The first Corvette (1953) was only available with the Powerglide, a choice made out of necessity (lack of a suitabl manual). And the automatic transmission was seen as futuristic at the time, seemingly suitable for a Motorama car that was put into production. And a healthy percentage of later V8 C1 Corvettes were ordered with the PG, although it was not available on the high-output small blocks.
And it wasn’t available with the big block that arrived in mid-year 1965. But in 1967, the last year for the C1, the seemingly odd combination of 427 and PG was available, and the ultimate version was with the optional 400 hp 427 (7 liter) big block crowned with triple carburation. Chevy’s newest engine and oldest transmission were mated in a final blow-out tribute to the Powerglide. Care to guess how fast one could go in Low gear?
Before we take a stab at answering that, let’s also pay homage to the fact that the 1953 Corvette was the first production car to have a floor-shifted automatic transmission. It emerged directly out of the side of the transmission, undoubtedly an expedient way to add a lever to the Powerglide’s existing shift mechanism that exited there.
The gear markings were discretely labeled on the knob, which reflected the older PG shift pattern, and in this case, was also the reverse of the typical floor shift to come, with P at the bottom. The Corvette’s PG gear pattern went through several convoluted evolutions, but maybe that’s a story for another time (or not).
Eventually it morphed into the familiar PRNDL, as seen here in this 1963. The Powerglide’s take rate dropped steadily through the years, and was available only with the mildest engines, the 250 hp and 300 hp 327, the latter being standard since 1966.
Although the big-block engines became available in 1965.5 (396) and 1966 (427), they were only offered with the four-speed manual in those first two years, even the hydraulic cam 390 hp version of the 427.
But in 1967, Chevrolet graced slush-box lovers with a one-year only offering: the Powerglide behind either the 390 hp four-barrel 427, or the 400 hp tri-power 427. The mechanical-lifter 435 hp engine was still off-limits, as was the 350 hp 327.
The question you’re undoubtedly asking is “why not the excellent THM-400, which had been in production for several years and was available on big-block Chevrolet sedans?” Well, I didn’t have to Google for an answer: it obviously wouldn’t have fit under the C2’s rather petite transmission-hump floor panel. In 1968, the new C3 and its giant transmission tunnel and console finally played host to the THM.
The pictures of this restored red ’67 Corvette convertible I’m showing you is one of these rather unusual and rare cars, a 1967 427 with the 400 hp tri-power, Powerglide, and even air conditioning (power steering wasn’t available). How many of these unicorns were built in 1967? Exactly 207. Another 392 were built with the 427/390/PG combo. A gentleman’s express.
So let’s get back to that question, of how fast one of these 427 Corvettes could go in Low gear. Would you believe 90 mph? That’s my calculation based on the tallest available rear axle ratio of 3.08:1, and assuming the 427 could be coaxed to spin a bit over 6000 rpm. The 427/400 made its maximum hp at 5400 rpm, but as the tach here shows, red line wasn’t until 6000 rpm. Just how fast one of these would rev is subject to debate and how good of a tune-up it had. With an even taller axle ratio, it could have topped 100 mph in Low. Top speed (in High gear) was in excess of 140 mph.
We can safely assume that this Corvette was the world’s fastest two-speed production gasoline-powered car. For that matter, the 427 Corvette had the kind of abundant torque that would have worked pretty well even if the Powerglide had still been in its original one-speed mode. Now that’s something to mull over, at high speed.
Related reading:
Powerglide: A GM’s Greatest Hit or Deadly Sin?
Automotive History: From Powerglide to 4-speed – The History of Transmissions on Early Corvettes
Two-Speed Automatics vs. Three-Speed Manuals: When 2=3, And Then Some
The Corvette, to me, has always been one of the few cars that seems like a total disappointment as an automatic. ‘Vettes should have standard transmissions.
With that being said, what a weirdly optioned car! A 400-hp factory Powerglide? It’s so weird I almost like it.
I have to wonder why Chevy made Powerglide available with the 427 for just this one model year, when the THM-compatible C3 was right around the corner. Did Chevy feel pressure to make an automatic available with the 427, due to the rising take-up rate of automatics across the industry, and didn’t think they could hold off for even one more year? I’d be curious what percentage of ’67 Corvettes had automatics, both in general and among the two versions of the 427 that were available with Powerglide.
I think it’s because dealers wanted to sell optioned up (more profit) big block corvettes to nice couples standing in the show room. One wants 400 hp, the other insists on a automatic. The smiling salesman says “well folks we can do that.
Back in my day a person was thought to be outta their mind to place an order for a 67 Corvette they had not seen much less one with automatic transmission. My factory order was made in August and, due to GM strike in St Louis, late delivery came on November 30 1966. Even now 48 years later I can still feel the rush that came from shifting that 4 speed hooked to the BB 427.
In recent years I have been behind the wheel of a like new 1967 437/400 with power glide and I believe it’s quicker than my first with 4 Speed. It is weird but you probably would like it!
My neighbor in Lewiston, NY had a 67 PG 427 Vette roadster. It bafflled me back then but with inclement weather any time of the year, at least it would be driveable. 🙂
I would like to add I’ve been fortunate enough to buy two new Vettes in the past five years, but if that Vette from Lewiston is still alive, I would love to know if it is for sale.
Hello, Paul Niedermeyer
Very nice article. One thing, my 1967 L68 Power-glide came w/power-steering!!
I have owned since 1988 an original restored to perfect condition 1967 Maroon & Black 427/400 power-glide w/power-steering, side exhaust, hard top, with tank sticker. which i will be selling at 2019 Amelia Island Concours d’Elegance on Friday, March 8. feel free to contact me about Power-steering.
Richard rickyperry21@gmail.com 321-961-2200
Sure you could rev it to six grand, but the big Harrison A6 compressor wouldn’t like it for very long.
I’ve driven PG equipped cars, and none of them ever felt that satisfying to drive.
Slip-n-slide – Powerglide! for sure. But it is an dang near indesctructible transmission if you got the torque to back it up.
My dad had a 1963 corvette convertible with powerglide that he bought new when he was commuting to work in Los Angeles. He even took it with him to London for a year on the QE2. I believe he said he had the 327/350 and I think I’ve been able to verify that was a potential combo. I think I also read that the car was nearly as fast to 60 as a four speed because of a combination of nearly no wheel spin, strong torque multiplication and no shifts until after 60 mph.
I’ve looked on line and it must have been a 327/300
If memory serves me, I believe only the 250 and 300hp 327s were available with PG. The two top solid lifter engines, 340hp 4bbl and 360hp fuelie were stick only.
My 1963 IS a Powerglide. Couldn’t choose, that’s how it came to me. It’s a base 327/250hp convertible, now without the canvas on its top since it doesn’t go out in inclement weather. Even the base engine delivers gobs of torque through the PG’s torque converter though it must be admitted: in the process of doing work on it, the engine has been “massaged,” but is still docile around town.
Being a 327/Powerglide, it gets called a “girl’s Corvette” at times.
There are lots of high-horsepower drag cars that run beefed-up Powerglides. They’re light, durable, and have low parasitic losses. In a Corvette, sitting behind a big block with its wide power band, the PG may work very well.
Certain, torque multiplication is not a big concern with a 427…
As much as I dislike two speed slush boxes , I bet this thing is a hoot to drive .
-Nate
I agree completely! Just put the hammer down, hold on and enjoy the mountain of torque
23 Sep 2014–The day forever remembered as the day my first 1/25 model kit became an article on CC.
I would have thought the turbohydramatic would have been the option, but that is available for 1968. Based on the 1967 brochure, 6000 RPMs with the 3.08:1 axle results in about 87 MPH.
I would caution everyone that the Chevy sedans may have 3.36:1 axles and the engines may not want to run @6000. Tire size may also be smaller…
Was Pg a popular option on the high HP corvette? The PGs small size is I suspect one of the main reasons GMs Vauxhall and Holden divisions went for the powerglide previous automatic models had different floorpans to accomodate the hydramatic and made automatic trans an awkward option at their far flung assembly plants and an expensive option in any case automatic cars had to be dealer ordered here and the correct floorpan included in the CKD packs to produce one or the car had to be brought in built up more expensive again.
Back in the day an automatic equipped car was easy to spot in New Zealand especially if it was GM they all sported whitewall tyres as factory fitted standard to announce to the world the owner either couldnt drive or had spent extra as an upgrade.
No. If you read the post, the actual production numbers are in it.
I have ridden in a 67 427/mt and it moved pretty well. Owned a 75 350 mt and that also moved well. Have not been in a vette with a slushbox.
Paul: I have owned a wagon with a 350/350. I understood that the th350 was essentially a pg with a third gear. I know that it fits in a pg hole without altering the driveshaft. Isan article coming on GMs th350/400? The th350 in my 77 Impala was about my favorite ever. If something that durable had been available I would probably not be driving a mt.
I had an 84 and an 86 Corvette with automatic transmission, but they were the electronic 4 speed overdrive units. The 86 was very fast, I once got close to 200 KM/hr.
The TH350 was a smaller version the TH400 as far as I know. Designed for smaller engines.
The TH350 is not a smaller version of a TH400. They are similar like apples and oranges. They are completely different in appearance, design, and the mechanical ways each accomplishes shifts .
Other than being called automatic transmissions, the PG had nothing in common with the 350/400THM.
Out of those 427/PG production numbers, how many had factory a/c and/or factory side pipes? “Unicorn” is an understatement!
ah the wonderful days before the EPA had to certify every powertrein combo…”does it fit? can we sell any?Yes? Build it!”
Before settling on my ’75 automatic Stingray, I thought about a manual-trans version- until I sat in one. There was nowhere to rest my size 13W clodhoppers except the clutch pedal, which isn’t exactly conducive to long clutch or throwout bearing life. Pass.
In a car as light as a Corvette combined with a powerful tri-power big block, a 2 speed is probably really all you need. But it’s still a strange sounding combination. Not the best for fuel economy for sure. Good for drag racing.
Unboosted steering: no wonder these were rare, having to work the steering if not the trans. How much effort was it with that big-block? At least the engine is where it should be in a proper sports-car: behind the front axle-line.
“The first Corvette (1953) was only available with the Powerglide, a choice made perhaps out of necessity (lack of a suitably-strong manual) or because the automatic transmission was seen as futuristic at the time. ”
Chevrolet engineering didn’t believe the existing three-speed was a suitable choice for a sports car. They felt the Powerglide was Chevrolet’s best transmission at the time. It’s only alteration from the passenger Chevrolet was altered shift points. The short turn around time for the Corvette also meant there was very little time for development of a new manual transmission. Due to the triple carburetor setup, a column shift linkage would not work as it interfered with the rear carburetor. The Powerglide was easier to use a floor shift with verses creating a shift linkage for the three-speed. By 1955, Chevrolet had time to develop ad a new close ratio 3-speed with floor shift for the Corvette.
Chapparal had a direct line to Chevrolet engineering. Chevy could see the 2 speed was all you really needed for a street or racing car.
Chapparal was running the two speed automatic for 4 years before this 427 Vette was built. Chapparal ran 327 engines and went to the 427 in 1967. Even a 327 beat up the hard tires in the early ’60s, the automatic was gentle and didn’t spin the tires everytime you got on the gas. By the late ’60s, the tires got bigger and grippier, so they could run the big block and a regular manual trans if they wanted.
Chaparral started with the two speed because traction was the limiting factor in acceleration. As traction increased, Chapparal switched to three speeds.
This reminds me of a Ford GT40 I saw a few years back that had a 2-speed auto transaxle behind the 7-litre engine, 1.49:1 first gear ratio and 2.5 final drive. 2nd gear was 1.04:1, no direct drive after all. I remember it had the top speed in first gear written on the info board, I can’t remember what it was exactly but it was in the range of 120-150 mph! Top speed was a bit over 200 mph.
Another interesting find!
The 6,000 RPM tach, I think is incorrect, however. This engine, RPO-L68, was considered a PASS (passenger) engine, unlike its RPO-L71 brother, which yielded 435 HP due to a solid lifter cam and big valve/port heads, all supported by 4 bolt main bearing caps. The L71 was considered a HI-PERF (high performance) engine with a 6,000 RPM redline.
This L68 engine should have had a 5,500 RPM redline tach, primarily due to the massive size of the crankshaft and its retention by 2 bolt caps. Rat motors were notorious for spinning bearings if the RPM was pushed too far so the preferred approach was to recommend moderate maximum engine speed and avoid expensive (to Chevrolet) warranty repairs.
This combination dispels the myth that the PG wasn’t durable. It clearly was with the right clutch pack and sprag installed, just not very sporting.
Are you saying it “should have a 5,500 rpm redline tach” because it’s your opinion that this engine shouldn’t exceed 5,5500 rpm, or because you know that it actually came with a different tach? There’s a difference.
I find it odd to think someone would put in a different tach, given that this is clearly a PG car. The L68 made its rated hp at 5400 rpm; typically there’s a not inconsiderable spread between max rated hp and actual red line. In your opinion, that would only have been 100 rpm. That doesn’t seem quite right to me.
I’m really perplexed about your last comment. I’ve never heard of the PG having a rep for weakness; in fact, only the polar opposite. It seems to have a rather bullet-proof rep, and has been adopted enthusiastically (with some mods,of course) by drag racers, mudders and pullers, mostly because of its rep for being to take abuse.
In all the years that I’ve been writing about older cars, I can’t come up with a single memory of a comment about someone’s PG crapping out, or such. I’m sure it happened, but if I had to rate it on reputation, I’d say it’s probably the most durable automatic built, perhaps along with the Torqueflite 727.
It’s not my opinion, it’s a fact that the 2 bolt motors were “recommended” not to exceed 5,500 RPM; the 4 bolt motors (396-375; 427-425; 427-435), were maxed at 6,000 RPM, maybe 6,200 RPM for the L88 and 454-450 but that’s really pushing it.
I don’t know what the deal is with the tach in this particular car but I would never take a passenger version of a Chevrolet big-block, which a 427-400 is, beyond 5,500 RPM; I have owned a bunch of big blocks and they don’t like high RPM unless they are substantially modified.
I see the entry posted blow and would like to know the source; that is not the maximum horsepower peak, your accompanying chart dispels that, so what does it represent?
As for the PG’s being weak, I used to work for a Chevrolet dealer in the early ’70’s and saw a lot of them leaking and apart. They were good with small to medium sized motors and did well if not beat upon; yes, good longevity. Beyond that they were notorious for a slipping low band which usually leads to metallic particles and problems, thus the name “Slip and Slide Powerglide”. You are correct, they were favored by drag racers but those versions have nothing in common with a street version other than the name and the fact that they have two speeds.
I see the entry posted blow and would like to know the source;
Those numbers (6000 for the 390/400 hp 427) are the factory tach redlnes. Check any Corvette forum.
Paul, not sure how you read rpos last comment regarding strength of the PG. You both seem to agree.
A quick search turned up this –
L75 327/300 5500
L79 327/350 6000
L36 427/390 6000
L68 427/400 6000
L88 427/430 6500
L71 427/435 6500
You saved me the effort 🙂 And that confirms what I suspected.
This car has two speeds.
Fast and FASTER!
That is what I have always heard when it is behind a powerful engine. Years ago, my then girlfriend had a ’72 Vega with a PG. It was no wonder she would always “steal” my Z-28 whenever she could.
However, my main question: Would a Hydromatic been a better choice?
The old four-speed Hydra-Matic (which I’m sure wouldn’t have fit) would have been a big hassle with a 427, I suspect, because low gear would have been too low. A Dual-Range Hydra-Matic had a 3.82 first gear (4.09 on some ’55s), which even with a 3.08 axle would give you 11.77:1 and probably a lot of hopeless tire-squealing. Even the ‘Vette’s wide-ratio four-speed with a 4.11 axle was only 10.36:1 overall in first, and with the 427, that was already a ratio only a tire salesman could love
Bill Mitchell, VP of GM Styling and the father of the Sting Ray, had a custom ’67 Vette built for his wife, which was very similar to this car. The car was a COPO car, ordered personally by Zora Arkus-Duntov and delivered to the GM Tech Center for customization, reportedly after Bill Mitchell himself walked the car thru the production line in St. Louis.
http://www.mecum.com/lot-detail.cfm?lot_id=bg0609-80925
The Madam Mitchell’s car was a white exterior w/red hood stripe and custom red leather interior and was built with the 427/400 & PG drive train, A/C, side pipes & alloy wheels. Of course, since Bill Mitchell was involved, there were many custom styling touches added to this car, from red accents in between the fins of the wheels to a fully detailed undercarriage and suspension, with the front A-arms painted red.
Mrs. Mitchell sold the car privately after two years, and it went thru several owners until its provenance was revealed during restoration.
You almost had me with this one until I read “side mounts”. I can’t imagine him buying a car for his “wife” with side exhaust. Ouch.
I can’t either. She only kept it for two years so probably drove it twice!
Of the 207 1967 Vette w/ the 427/400’s supposively built with PG or 4_Speed Trans , does anyone out there happen to know how many of these 207 Vettes had the 4-Speed, factory a/c + convertible? I’m trying to narrow down the numbers on mine. Thanks
I may have info that will help you. Off and on I’ve. Been trying to locate my first 67 427/390 I ordered special built in fall of ’66. I now have one identical color combo (marina blue/white) coupe 427/400, PG,A/C, P/S . Owned 10 years, rarely driven. will take 120k for it if you would like to have a pair of PG w/ air. Great conditionI, i
I will see what research I have and post in a few days I come up with anything beneficial for you convertible.
LB
A rare find and an impressive one at that. Slip ‘n slide Powerglide in a 427 Corvette.
90 mph in low gear?!. (And I thought the 10mph in first gear (4sp SM465) in my dad’s 1968 GMC was impressive. LOL)
I guess I missed it in the article and reader’s comments, but how was 0-60 and 0-100 acceleration with the powerglide? Could it beat the 4sp manual?
Could a PG with the same engine beat a 4sp?
I HIGHLY doubt it!
That ’53 looks to be an exquisite example of well executed design engineering. The dash display looks harmonious in its layout. Right down to the details on the shift lever, a true masterpiece.
Wow, I missed this the first time around. I would never have guessed that this combo existed, but then I am not expert in Chevy-speak.
From what I understand the Glide is a tough old thing and could surely handle the kind of power these big engines put out. And as you say, a high-revving powerhouse like this would work around the PG’s shortcomings as well as anything.
My Dad (a GM man born and raised) always referred to the PowerGlide as “PowerSlide” – and he owned a few of them, but I believe always hooked up to the 283 V8.
I’m happy with a 3 speed auto in my 67 Mustang. The only time I have shifting issues is when I’m having fuel delivery issues. 😉
Following a Diagnosis of IBM, a severe muscle desease, I have opted to replace my M21 with a TH-350C Automatic. My Corvette is an L71 427/435 (JE) Coupe. Although this combination was nt an option for a C2 L71 in 1967, the switch will offer me a chance to continue driving this amazing Historic Car.
Choosing the Th350C (LOCK UP Converter) or TH-350 allows for little to no modifications to the Chassis or transmission tunnel. So a reverse conversion is not problematic.
No experiences with any of those combos specifically, I’ll still chime in.
Not a domestic car fan
Not a GM fan
Not a Corvette fan
Not an A/T fan
But I’ll still chime in.
PGs somehow have a reputation 100X better than the 2 speed Fordomatic. The seat of my pants bears that out. It’s been a long time, but I don’t recall them being gutless off the line, or anywhere for that matter. A loose torque converter, the right engine and torque curve, with the right diff? Maybe? Dunno. The ones I drove were long ago, and I wasn’t quite as aware of details. But for an A/T they drove well, as opposed to the FOM which had two modes, slow and gutless.
So I’m guessing for those who didn’t like or couldn’t do 3 pedals, they still provided a nice adrenaline rush. The younger me would have disdained it, if you can’t drive a proper transmission, don’t bother. The older me still has some of that in me, but even if they are poor form, so what, let the customer and MFR decide.