Curbside reader cadiman67 writes; Hello: I have a 1969 Cadillac Deville (Convertible) and am not happy with the ride – it feels very harsh when I go over any potholes or similar imperfections in the road. I have replaced the shocks and springs and rebuilt the front end. When I look at the underside of the vehicle I can’t help but think that the 14 rubber body mounting pads may be causing this problem since the rubber has obviously hardened over the years but no mechanic is in agreement with me. However, none of them admit that they have ever replaced all of the body mounting pads on a vehicle so they can not say for sure. Have you ever replaced all of the body mounting pads on a vehicle? If you have what was the reason for doing so and what were the results on the ride? A few years ago a coworker claimed he had that done to his late 70’s model Ford station wagon and was amazed at the improvement in the ride but he is the only person who has ever said that. Everyone else insists the body mounting pads have nothing to do with the softness of the ride. I would hate to spend the money to have them replaced and then still have a harsh ride. What do you think?
First, thanks for your inquiry. Yes, body mounting bushings are part of the system that isolates you from the bumps in the road. There is a reason that they did not bolt the body directly to the frame. However, they are only part of the isolation system, so let’s start from the ground up.
Typical sidewall markings
Tires are the first part of the system. When the tire hits an imperfection in the road, it flexes to absorb part of the harshness. The key to this working properly is a tire with the proper load rating. This is not to be confused with the “maximum load” stamped on the tire. The inflation pressure is what ultimately determines the tire’s load capacity. Back in the day, some tire retailers provided a Load and Inflation Chart with the purchase. Unfortunately, those charts are not included with the purchase anymore. Because that info isn’t as available as it once was, few mechanics and tire installers calculate the proper pressure when the tire size is changed. Worse yet, there are those that just put 32psi or some other value they consider “right”, or inflate every tire to the max pressure on the sidewall without even consulting the tire placard.
1969 Cadillac tire pressure decal
However, thanks to the internet, load and inflation charts can still be found. A little Googling turned up this, Tires 101 from Toyo, which includes a guide to using Load and Application tables in determining the proper inflation pressure of a replacement tire. Of course it does not include the old 9.00-15 tire size so we can’t follow the directions in guide letter for letter, instead, we’ll have to do some calculations.
1967-68 Cadillac tire decal
It used to be common to list pressures for average and full rated load, but even in the 60’s we were starting to see the idea that the average consumer couldn’t be trusted. Looking online, I found the curb weight of the 1969 Cadillac Convertible is 4590lbs, add to that the max load and we need tires than can carry about 5700lbs. Looking up the available replacement springs showed that the fronts are rated for 2810lbs per pair while the “Heavy Duty” rears are rated at 2802lbs per pair. Since the stock tire pressures and spring ratings are equal front and rear we need 1400~1425lb load capacity per tire at full rated load. In cadiman67’s follow up E-mail he noted his Caddy is wearing Michelin 225/75r15 tires, so we’ll take that info and look at a Load and Inflation Chart. Since I can’t find a data on a current Michelin tire in that size we’ll compare the various types of 225/75r15 tires as found in the Toyo publication.
P-Metric tires
Load                              [  Standard Load  ]    [Extra Load]
Index       Size           26    29    32    35     38    41 psi
102 Â Â P225/75 R15Â Â 1631Â 1720Â 1797Â 1874Â Â 1951Â 2028 lbs
ISO Metric (no P prefix)
Load
Index      22     23      24     25       26      27      28      29      30     31       32    33     34     35    36 psi
102Â Â Â Â 1246Â Â 1312Â Â 1348Â Â 1378Â Â 1444 Â 1481Â Â 1499Â Â 1565Â Â 1631Â Â 1654 Â 1687Â Â 1753Â Â 1781 Â 1819 Â 1874lbs
Light Truck               [     Load Range C    ]         [ Load Range D ]
Size                      35    40       45       50          55        60       65 psi
LT225/75R15 Single 1445 1585  1720   1875   1980   2100   2205
Also note this warning from the Toyo Guide:
WARNING! Please note that size for size, LT-metric tires require higher air pressures
to carry equivalent loads of P-Metric tires and that any failure to adjust air pressure to
achieve the vehicle’s load requirements will result in tire fatigue and eventual tire failure
due to excessive heat buildup. Due to the higher PSI requirements of LT-Metric tires they
may not be suitable for replacing O.E. P-Metric tires because of the ride harshness that
results from higher PSI.
I’ve included the LT tire specifications because I’ve seen many times where tire stores sell LT tires for these Cadillacs citing that they are such heavy vehicles, that “they need a truck tire”, fact is the curb weight of a 1969 Cadillac convertible is only 75lbs more than a 2012 Chrysler 300 AWD.
So, recommendation #1, after reviewing the links above and making the calculations yourself, is to check and adjust your tire pressure accordingly. Note the minimum inflation pressures in the above chart, they differ based on the type of tire. The other thing to consider is that the original tires, being of the late numeric system, were an “82” series tire while your current tires are a “75” series tire, combined with the fact that your current tires are smaller and you’ve got much less sidewall to deflect and absorb the bump. The 9.00×15 has a 7.3″Â sidewall while the 225/75 is only 6.6″ high, a loss of about 10%. Also, consider when selecting your inflation pressure that the lower the inflation pressure, the less responsive the steering will be and the lower cornering ability will be. It’s up to you to determine the best trade off for you.
Lower control arm bushing
The front suspension has been rebuilt with the springs and shocks replaced, but it isn’t clear if the problem existed before the rebuild or started after. One thing that is often done improperly when rebuilding a suspension involves the tightening of the bolts that secure the control arms. If you look at the picture above, the sleeve that the bolt goes through is serrated. With the stock bushings it is important that the through bolts are not tightened until the full weight of the vehicle is on the wheels and the suspension is allowed to properly settle. If an alignment rack with slip plates is not available that means driving the vehicle back and forth a few times. If the bushings are tightened before the weight of the car is applied to the suspension, the bushings will be preloaded when the weight of the vehicle is placed on the suspension. This will cause them to excessively resist suspension compression and to loose their ability to effectively isolate road irregularities from the chassis.
Front shock
The shock absorber also plays a significant role in how the vehicle rides. Shock absorbers are often very model specific but the aftermarket only offers a one size fits all. Typically for many cars today the only shocks available are of the Heavy Duty variety which are inherently stiffer than the original standard duty versions. The shock’s main purpose is to keep the tires on the road. They do this by resisting, or slowing down, the movement of the suspension. Valving that is too restrictive will cause a harsh ride. With the stud style mount as used on the top of the front shock if the bushing is not properly installed it can create a situation where it will transmit impacts to the frame. What about the rear suspension? All the same rules as to shocks, bushings and proper installation apply there too.
Suggestion #2 would be to verify that the bushings and shocks were properly installed. If the bushings were replaced with polyurethane instead of the factory rubber style, they will transmit more of the impact to the chassis.
Now on to the focus of your question, the body mount bushings. Yes, I have replaced body mount bushings on a vehicle before. In that instance it was a case of project creep, (seen here) I had the body off of the frame for other repairs and I figured might as well replace the body bushings while they were accessible. However the only bushings available for that vehicle were polyurethane so they are stiffer than factory rubber bushings. However I did not notice any significant change in ride, but then again it was a Scout II so I don’t expect it to ride like well…… a Cadillac.
I would only consider replacing the body mount bushings as a last resort, and even then only if you are really committed to keeping the car for the long run.
So, readers what do you say, have you ever had the body bushings replaced on one of your vehicles? If so, what was your reason and did you notice any difference in the ride? Have you ever had a car whose ride you considered harsh and if so what did you find, if anything, that fixed the issue to your satisfaction?
Do you, like cadiman67, have an issue with your Curbside Classic that you would like our readers to weigh in on? If so send your questions to CurbsideClueless@Gmail.com.
Have you given the springs time to settle? They’re going to hit a bit hard until they “break in”, you may even see a bit of settling in ride height after a while.
You can also use an old racers trick to determine proper tire pressure.
Go to an open parking lot where you can drive in a straight line for a couple hundred feet. Use white chalk or shoe polish across the tread on all four tires and drive forward long enough to get a wear pattern in the chalk line. If you’re over inflated the chalk in the center will wear off, underinflated and the outer edged will show more of the wear.
I did this on my truck after getting 32s because it was hitting hard and the tires were screaming at highway speeds. I wound up with 40psi front and 36psi rear, ride improved greatly, handling didn’t change, and oddly my mileage improved slightly.
We did body mounts on our 73 Chevelle years back and really didn’t note a huge difference. But that car was being built for non-luxo uses and we weren’t really looking for an improvement.
No experience doing body mounts. Is it possible that the springs have higher spring rates than stock? Also, the tires are the first thing that comes to my mind. A larger sidewall would likely help a lot. Still, about any radial tire would probably be better than this car with its OEM bias belted tires.
One other point, I presume that you drove the car before the new springs/shocks/suspension and it was OK? Or are you in a club where you would have access to another similar car for comparison? If not, could there be something about a 40+ year old car. I never thought that these rode as well or were as quiet as Lincolns of that same era. I think that we have become spoiled by how smoothly newer cars ride. Even the best of them from the 1960s are not necessarily what we are used to today from the better larger sedans.
I’m guessing tires/inflation or incorrect spring installation since you’ve appeared to have covered off all the usual suspects. I really don’t think that there is enough “give” in the mounts to absorb that much shock unless they have all dryrotted out.
I have a ’69 Fleetwood with the cheapest set of Walmart Uylesses tires on them, inflated to around 30 PSI and it rides fine. A ’68 Fleetwood is on Firestones and rides a touch harder. From memory, the old man’s ’67 Fleetwood had bias ply on them, and they scrubbed and squealed their way around corners at normal speeds. The radials made a huge difference to these cars, but you have to recall that the bias plies were intended for 22-26 PSI at most. The average radial with it’s stiffer sidewalls and higher inflation is probably the cause for most of the ride issues. I’m running 235/15/75 on all my 60’s to 70’s Caddies, and 225’s on the 77’s and up.
Judging from the photograph, the stance of the car looks right, and if you have replaced all the springs/shocks/bushings with the correct pieces, it should right nicely. A lesser possibility is that your springs might have a higher rating or be Fleetwood 75 springs and have the heavy duty rating. Sometimes it is hard to get the proper springs for an oldie at your parts store, and they can substitute a different model or rating if they can’t get the original stuff.
I find that the cheaper tires with the softer sidewalls make a better compromise for these cars. The ’68 originally had Micheleins on it, and the ride was far harder over tar strips, etc. Today’s tires have much harder rubber and sidewalls to go with long road life, hence better handling, but less bump absorption for old cars that didn’t have “radial tuned” suspensions as was found into the 70’s.
Don’t know about you folks in the US, but getting thin line whitewalls up here is getting to be almost impossible in the 215 to 235/15 range that I typically use. Even parts for these cars tended to dry up after GM’s issues in 2008, and there is little aftermarket support.
The actual car in question is not pictured, that is a random shot found on the web.
I agree with you that tires are the likely culprit. New ones, properly inflated, will probably make the biggest difference.
But radials don’t have stiffer sidewalls than bias-plies; the opposite, actually. That’s one of their key structural differences, and is partly the reason radials all bulge at the sidewalls, unlike bias plies. The radial orientation of the sidewall plies allows them to flex without the internal friction of bias ply sidewalls.
Playing with the tire pressure may help a bit, but I doubt there is much more you can do. I think the manufacturers have improved general vehicle ride characteristics in the past 43 years, and thus our “baseline” of good ride has changed. I have a 70 DeVille, and my buddy has one as well. Several years back I too changed the complete suspension (new springs, bushings, shocks, ball joints, etc.) While overall I think the ride improved (it is certainly safer), It still crashes a bit over potholes and bad road. I run 235-75-R15 tires, and inflate to 28lbs. I bet that going back to a bias ply (Coker Tire) would improve the rough road ride, but at the detriment of handling and safety.
What I have noticed is that my car with the new springs sits about 4 inches higher at the top of the front fender than my buddy’s car (his car isn’t any better with potholes). I can’t remember the spring rate, but I recall having a detailed discussion about the car with the outfit that sold me the springs…they were trying to determine the proper spring rate. I guess they tried, but I believe that I’m over sprung on the front end. My shocks sometimes cannot fully control the rebound from a pothole hit, and I get some secondary jounce. You may want to consider a softer spring if you find you are in a similar situation. I haven’t changed back because changing springs is quite a job for a backyard mechanic. I really don’t like lifting a car that high on jackstands, and removing and installing compressed springs is dangerous (if you do decide to do so, please chain the springs to the suspension during removal and install to keep it from flying if it slips compression).
I’m sorry I don’t have a solution, but know that you’re not the only DeVille owner with this issue
I forgot to mention it in the post below, but for what it’s worth, my ’69 had bias-ply tires when I got it. I replaced them with bias-ply twice. In those days I didn’t have the money to pop for a set of radials, even if it had occurred to me.
Each set was a different brand, and none of them rode or handled any better than the others.
I would disagree with you that bias ply tires will improve the ride. The radials have more sidewall flex. My very first set of radials was a set of 4 used ones, mounted and balanced for $60 in about 1981 (when I was a broke college student). They replaced bias ply tires on my 71 Scamp, that had never been a very good riding car. The radials completely changed the character of the car – it became a smooth riding car with those tires. I never put bias ply tires on a car again, new or old.
I must agree with JPC. My father’s 1967 Mustang orginally had bias plys on it, then switched to radials but they were very old and rode badly. He finally popped for new Goodyear radials and the ride improved greatly.
I was never happy with the ride of my ’69 Sedan de Ville. I bought it as a 23,000 mile “little old lady” car, so I assumed that everything up front was stock. She had the car serviced only at the dealer in Beverly Hills where it was purchased, so I had no reason to believe that it was not.
In addition to a harsh, non-absorbent ride that one would not expect in a Cadillac, alignment was a big problem, making freeway driving an unsetting prospect. Every trip to the mechanic for service or repair included a complaint from me about the front end exhibiting this or that problem. Suspension bushings were replaced at least twice. New shocks, multiple alignments and tires didn’t help very much, if at all. In short, it was never right. My impression was that the suspension was under-designed for the car. Truth is, aside from the styling and the superb drivetrain, it just wasn’t a very good car.
I learned to drive in Caprices and LTDs of the same vintage and they had much cushier rides than the Cadillac. My 1978 Caprice (non-F41) both rode and handled better than any of them.
Appreciate the advice on the control arm bushings! I’ll be refering back to this when I redo my two classics – ’57 Handyman and ’68 C-10 2wd.
Its built like a truck BOF what did you expect?
No.
One thing not mentioned so far is the AGE of the tires. Collector cars and other cars that don’t get driven a lot are often riding on old tires. Tires harden with age. In 2001 I bought an ’89 Caddy with only 53K miles and it was riding on a set of Vogues it probably had since new. While you can theoretically get 80K miles out of Vogues, and some other tires, after 11 years they rode like rocks. Old tires can also be a safety issue as they are more likely to blow even if the look great (ask me how I know). I’ve seen varying recommendations of when you should replace tires due to age regardless of wear, but 7 years seems pretty common.
Good point, in addition to the hardened rubber potentially causing a harsher ride the traction is significantly diminished.
A good reference to determine the age of your tires can be found here http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=11
The question of how old is too old does have a lot of different answers, but not one definite answer. I’ve seen Toyota owners manuals where they say that tires should be replaced at 5 years regardless of tread remaining.
This is what I came to say: age. The age of the tires may be the culprit here.
You know, I had a friend with a 2004 Jaguar S-type that rode like a truck. You felt EVERY bump in the road; like it was breaking your back.
I took a look at his tires and they were old, lacked tread, were mismatched and generally worn out. They were WAY overinflated by the lube place he used for oil changes. I bled them off and the ride got better.
Then he bought new tires the next week and suddenly the new car ride was back. It was mainly overinflation and old hard tires that gave him a very horrible ride.
I have to agree with the tire mavens. I used to be of the mind that anything of the proper size would do the job. Then, I happened upon an internet deal for a set of Goodyears for the price of no-names. My beater Catera is now worth every bit of my steep learning curve. But, I still use bias-ply on my Hudson. It’s never crossed my mind to change to radials on car 60 years old. Has anyone out there used radials on a 50’s era car? In stock condition?
I have put them on 60s cars (66 Fury III and 68 Newport.) The ride is much smoother. The tradeoff is that the suspension is taxed more. With the bias plys, when you turn too quick, the tires will squeal and lose traction so you do a little slide. With the radials, the tires are much stickier, so they will grip way beyond what the suspension expects, so the car will probably lean more in the turns. I found the tradeoff worthwhile just for the added smoothness, as the suspension in my Mopars was reasonably stout and I was not racing around with them anyhow.
My 66 Deville convertible had a rougher ride than any Cadillac I’ve ever had. My 78 Eldo wallows about like a marshmallow, even with 12 year old Michelins.
One thing to think about. I don’t know about other parts of the US, but in Western PA, the roads are awful. Secondary state highways are tarred and chipped, and this makes for a rough ride in any car. I travel one such highway a great deal, and in certain areas, I’ve felt that something major was wrong with the car.
The road through my town was paved and widened last year. When travelling over it, the feel is very uneven in any car I own. Roads just are not as good as they used to be. Even the individual segments in the interstates are uneven, making for a rough ride.
The roads may be part of the problem. But just as likely, being used to a modern car can make driving a vintage car totally miserable. I venture to say that drive that 69 Caddy for a couple weeks exclusively, and it might not seem to ride as bad. And of course, the creaking and squeaking of a convertible adds to the rough feeling.
Please do not go down this road. It will end up like every other forum board with clueless people spouting false/inaccurate/wives-tales information on subjects they know nothing about. Leave it to the dedicated forum boards, (there is one at least for almost anything made) please, we here are better than that. And lets just continue to enjoy our favorite Classics as is, and not try to repair them. Advice on most forum boards is like a doctor prescribing medicine by mail.
Some of the most satisfying aspects of owning old classic cars is, to me, working on them. The learning of alternative methods and improved materials has been revealing to this old man. Plus, my relative poverty would preclude me from paying anyone $100/hour – if I trusted them – to do my wrenching. I suspect this Cadillac owner will resolve this for himself. It’s his ass complaining to him – who has a larger stake?
Ok, just to prove the last poster’s theory, hmmm, just a guess, but ya’ll hucked on gas shocks, didnt you? Tsk, Tsk…
I’ll vouch for the impact of tire over/underinflation on ride quality. The TPS light came on in my VW GLI about a month ago. Hadn’t checked the pressure in the tires myself since buying the car at the beginning of the year. A quick inspection showed that all four where a whopping 10 psi underinflated. My car comes from stock with 18″ wheels and 40-series tires and the recommended inflation is like 39 PSI. I don’t know what the tolerance is on the TPS system, but there’s a reset button for the TPS in glovebox and I’m positive that they were underinflated like that from the factory.
I shouldn’t be surprised. It’s a VW. I’m lucky that’s the only problem from the factory (so far)…
Anyway, after putting air in the tires, the highway ride quality went from “decent” to “crap.” I didn’t even inflate them to 39, more like 36. My mileage went up 1-2 MPG though, so I’ve got that going for me. Which is nice.
They probably were set like that from the factory. The TPS reacted because the colder fall air lowered the pressure in the tire without any actual air leak.
Rant: I consider the TPS system to be a boondoggle because they’re recommending that tires be filled with nitrogen (at extra expense) because the humidity in normal air will cause the TPS sensor electronics to eventually go bad. Tire shops will also charge you more because removing and mounting a new tire will sometimes break the sensor if they don’t take care while breaking the bead on the rim and removing the valve stem. The recommend just unscrewing the valve and letting the sensor drop into the still mounted tire after relieving the pressure.
I know how and I do check my own tire pressure, dammit!
I’m deliberately installing heavy-duty suspension components on my ’72 Olds Delta 88 convertible to sharpen up its road manners. Up front I’ll be installing heavy duty OEM replacement coils made for a ’73 / ’74 Chevy Caprice wagon with the optional 454 big-block engine. Out back, I’ve already installed heavy duty police / taxi springs. I also have KYB gas shocks all around.
I realize this will come at some expense of the cloud ride that ’71-’76 B-bodies are known for, but I for one prefer a bit of a sporty feel to go with my luxury. My daily driver is a ’95 Lexus LS400 updated with 245/45R18 rubber.
I agree with the tire pressure comments–I once had a ’73 Deville sedan, and the ride was atrocious each time I got it back from the mechanic with 40psi in the tires. Let them out to the recommended 26, and it was back to magic-carpet quality.
That said, considering the Cadillac in question is a convertible, is this ‘harshness’ simply the juddery body/cowl shake that’s inevitable in most large convertibles, especially ones of this age?
That’s one of my pet peeves, and it’s the reason the first additions to the Miata I owned were a good shock tower brace and rollbar. No idea if anyone’s making chassis braces for ’69 Caddy convertibles, but if you want to settle the ride, it could be worth investigating. That, or a trade to a hardtop.
Had to fit new rear shocks to my Nissan recently; they ruined the ride. I hoped they’d calm down after a while, and true enough, 20,000km later I’ve got my plush ride back again. But those 20,000km were annoying…!
My local tyre-fitter/wheel alignment has also ruined the ride every time they’ve touched it. For some unknow reason whenever I get the car back from even a puncture repair I know it’ll now have 35-38 psi at each corner (tyre placard says 28) and a lumpy ride… A few minutes work with a properly calibrated gauge usually solves that issue.
Are you sure your tyres match the placard 28 is soft in the modern age and will adversly affect cornering. It sounds like a mushy Jappa
Yeah, they do. And yup, 28 is way too soft. I experimented for a while, and the best pressure is 32 – they wear completely evenly across at that, the ride’s nice, and it handles well.
I have to agree that the most probable cause of the rough ride is being a convertible. I’ve only owned 2 convertibles in my life, a 66 DeVille and an 85 LeBaron. Two complete opposites. My LeBaron has the worst ride I’ve ever encountered. Squeaks and moans, on the best roads, it rides terribly. The steering and suspension is tight, and probably the car rides as good as the day it rolled out of the factory.
The lack of a permanent roof and insulation accounts for the poor ride and noise. I haven’t had the Caddy since 1984, but I remember putting new shocks and tires and things improved, but still not great.
I’d like to hear about other’s experiences with convertibles, especially Cadillacs. From personal experience, they’re fun, but somewhat uncomfortable, top up or down.
Well I haven’t owned a Cadillac convertible but I have had a 1969 that is two steps down the GM hierarchy the LeSabre. I do not think it rode harsh or bad, it floated right along though it’s springs had definitely sagged over the years. I had 255/70 radial tires on it so it had a good size sidewall and I ran them at 26 psi. Definitely a softer smoother ride than most modern cars. Yes there was some cowl shake but it was not particularly terrible.
There is some truth to what Suzulight said, so I won’t speculate beyond offering my own experience. The 235/75-15 is a closer approximation of the proportions of the orginal tires on the biggest barges of this era. This will give the owner more contact patch and more sidewall, and the typical load rating for this size is 105, meaning it can handle 2000+ lbs. per tire at regular load inflation. I happen to run Toyos and they ride and grip better than the (ancient, definitely a factor) Michelins they replaced. The whitewall is correct for the era, if that matters.
I’d also ask the owner what kind of shocks he or his shop put on. As mentioned by others KYBs or Bilsteins will be stiffer than the less beefy but more forgiving “OEM” parts from Monroe or Gabriel. I put on a set of the latter last year and they reduced float in turns without beating me up over bumps.
My first car was a 1970 Cadillac Sedan de Ville and it really did ride like a truck. I remember thinking the suspension setting on that were probably stiffer to cope with the heavy weight of that car. If they were too soft the car would be a handful in terms of handling. The several hundred pound lighter 1986 Fleetwood Brougham I have now rides infinitely better.
try 235 75 15 tires – a little taller.
I’ve replaced body mount bushings on two cars – made it firmer, NOT softer
the last great fyll size gm until the 1977 full size, and 1979 el dorado.
what color is that. heather? or Iris?
Don’t know the color it is just a random picture I found on the web.
I believe that is Chateau Mauve Firemist. It is shown on a Coupe de Ville in the ’69 brochure.
Just an FYI, but I had a ’67 Coupe DeVille back in the day, and it did not ride as ‘plush’ as other family member’s Pontiac or Buick models of the same era.
I think the ultimate in having a really plush ride is my current ’96 Roadmaster wagon. Those seats are also fantastic. I like to say that they are so butter soft that they are curing hemorrhoids I don’t even have yet!
I have 70 series Hankook whitewalls on it, and even at 32, the ride is like butt’a, and it still gets 23 miles a gallon on a trip.
mg
I’ve done dozens of body bushings or cushions. That aint the cause of the hard ride. If you had a clunk or noise than I would suspect them. And I doubt it is the tires unless,like the others have said they were under/over inflated or just the wrong size. You know I have a theory. You’ve heard the saying “it’s only new once”. Yep, aint nothing going to bring back the new car ride. Parts degrade. You know when they screw a car together on the line they have mutiple choices on what parts to install. If you have, say F41 HD suspension than you get firmer bushings,springs,etc than one that doesn’t. But if you need to replace those parts than you only get one choice.The lowest common denominater. And it’s most likely the harder stuff. Trust me. I sell parts for a living. If it was me I’d do some hard research and concentrate on the tires. People ask me all of the time what to replace to make their car handle. You see, I’m the joker that shows up at an autocross with the ElCamino. Or Roadmaster wagon. Or 85 Turbo Riviera and than proceeds to dominate what ever class I’m running in. My only trick up my sleeve are the tires. Do a google on the quietest tires money can buy. I think that will be the answer to your harsh ride.
BTW I have lots of years in experience as far racing things. I could never win a class with out a little seat time. Which would be my second thing up my sleeve if there was any trick to being successfull at something.
My only other real “guess” would be the shocks. Even when they say soft ride they are usually valved so damn hard because unlike the OEM shocks they have to meet some type of lifetime warranty or what ever they are offering today. The OEM were usually the cheapest things money could buy. Smaller valves and pistons. Veggie oil for fluid. You get the point.
Some things to consider. When buying new springs most suppliers will sell you generic springs which result in a much higher spring rate than factory specs. Can increase harshness by 30%. Shock absorbers then were hydraulic and not gas charged. Gas- charged shocks also add to the firmness of the ride. Lastly bias ply tires gave a mushier ride. Although radials improve on handling
Another note- my mechanic (his employee) once incorrectly installed new shocks on my 64 Deville convertible. The front shocks were installed upside down! Also consult with the shop manual. The shocks line up with notched on the front control arms. The right and left springs are installed differently. One side has the notch in the front, the other has it on the rear. If the shocks are not sitting in the control arm properly they will raise the height of the front end. Caused me plenty of headaches to figure this all out.