This is a problem that has been going on for years, and up until recently nothing had changed. My car has a nasty shuddering vibration that starts at 70, gets worse through 75 and gets tolerable again by 80. It can be felt through the wheel and the whole car, yet when you feel the tunnel there's nothing, no heat, no vibration, nothing out of ordinary. The driveshaft and all the U-joints and the cardon joint were overhauled. I'm told it runs true. The rear axle is a 3.08 posi unit. Here's what's funny; the vibration is more pronounced on the right hand side of the road and not as bad on the left or in the passing lane. It doesn't vibrate through acceleration, but it gets slightly worse on deceleration or when loping along. There is a slight whine to the whole set up, it doesn't vary with power being added or not. I had the fluid changed just before I took it on this last long trip, and made sure that the proper limited slip additives were put in. There was a lot of metal and it was dark prior to being dumped. It's only just started getting worse, the vibration point is moving to a lower speed. At lower speeds, there's no driveline clunking or noises, just an easy pull. Turning left from dead stop, there's a hard two or three clunks that sort of feels like the drive shaft is bunching up, but then it releases and the car smoothly moves on. I can't find anything wrong with the steady bearing, the U-joints, or the cardon joints. It all looks okay. So is it the rear axle? Is it time to get it overhauled? Had a similar issue with a Sportwagon, except that when it hit into passing gear the tranny would downshift, the engine would roar but the car would decelerate...back off and it would pull again. What happens when the clutches start to fail?
That hard 2 or 3 clunks is almost for certain the rear diff. I know that on the ROA forum JZRIV had to remove a spring in the rear posi unit which then STOPPED ALL the clunking. On the other vibration I would say the driveshaft is out of phase. Most places tell you it's "Out of Phase" when they rebuild/service it, but in reality it's SUPPOSED to be out of phase as that's how it was designed from the factory. Tom T.
Thanks Tom, I guess I'm going to have to find a good driveline rebuilder. I'll do just about anything, but I can't go near rear axle oil, the smell makes me sick. Had a bad experience with it when I was a kid at my first garage job, ended up being soaked in it and having to live and try and sleep with that stink for a few solid days...man was I sick...and to this day, can't go near it. Dumb question; what is meant by "out of phase"? was that driveshaft deliberately built to run out of round?
Thanks Tom, I'll dig out my copy and start reading. It's gotta be the dumbest design for a driveshaft that I've ever seen, much prefer the 69 full-size or the Skylark layout, this mess with multiple u-joints, CV joints and steady bearings is a recipe for disaster. But then again, I never found fault with the old torque tube design either; never had an issue with one.
Marc, Just had a very lengthy in depth discussion about this on the ROA board. Much info given that very few are aware of.
If you have radials on the car, check to see that no belts have separated. Had that happen recently and it was a definite 'wobble'.
When I rebuilt the powertrain, the tranny foot that bolts to the mount had to be rewelded, but that was on the transmission itself. It now also has a new mount because the old one was very shot. The tranny case had a crack in the foot and a bolt wouldn't hold anymore so I had it fixed up. Not sure if it was warped to begin with, that's always a possibility. But there should be enough adjustment on the mount to compensate, one would think. I was recently told by the second owner that the car had been hit just aft of the passenger's side door. Apparently the original owner got drunk and found a fence post. Supposedly caved in the rear quarter just behind the door. I couldn't see any evidence of any buckling, but I probably should take the car to a frame shop and see if it's straight. Now I understand when I had the roof done why the guys at the upholstery shop asked me if the car had ever been in an accident. The second owner said the car tracked true and never had a vibration at high speeds when he owned it. I wonder though...but it does drive straight, doesn't dog-track or anything. The question is what caused the mount to break. So far, (10,000 miles after being rebuilt) there are no new cracks forming and it hasn't come apart. So it might have been the original hit it took over 30 years ago. The tires on the car are 3000 miles old. (3 years) Had them off and checked the balance, - they're fine. No noises coming from the wheels. Front end was serviced and bearings were repacked recently too. The central steady bearing crossmember is free floating within the frame; - not sure if there are any rubbers insulating it from the frame. There's a lot of undercoat covering the frame rails, but I didn't see any bolt holes with which to secure the crossmember securely within the frame. Looking at it, I assume it's supposed to float but I'm not sure. There's about 1/4" either direction play, so that might have something to do with it. I couldn't find anything in the chassis manual about that, nor was there a good picture in the parts book. The new u-joints I had installed made a big improvement, beforehand it felt like the car was coming apart at that speed. I probably should have had them all done, but the driveline specialists said they weren't an issue. They also didn't want to road test the car past the speed limit, so they got the car trued up for 60 mph. Another dumb question, what is the ROA board?
I have the same vibration issues and have yet to track them down. Have done many of the same steps as you have.
Have you put the rear up on jack stands and watched under it as someone runs it up to 70-75 MPH? Of course be careful but that will let you see the vibration if it is truly drive line related. What bothers me is the left/right side of the road. That sounds like a front end issue in some respects. Your toe could be off. Do your tires wear evenly?
Haven't tried that yet, but I will. I did a similar stunt with my Sportwagon when it had similar issues, and felt and saw nothing. The front end is fine, the tires are wearing well and the car holds a true track. I'm thinking it's when the driving forces switch to that axle, if I've got some bad clutches or a worn bearing in the rear end it would cause the vibration to be more evident. When I really nail the gas, both axles lock up and the vibration isn't so bad, but coasting or decelerating it vibrates a lot. The more I think about it the more it is becoming apparent that it's probably the rear end. If I drive the car and keep the speed below 60 there's no noise, no vibration, it feels like it should. However, if I go into the "vibration zone" once it's noisy and feels sloppy even at lower speeds. So I'm thinking it does have something to do with the clutches or some bearings that are wearing out. Either way, I'm going to send the car in and get the whole works overhauled. They told me years ago that the rear-end was not in the best of condition and that it might be the issue, I was just hoping to confirm that theory with some other owner's experiences before I pulled the trigger and paid out a lot of money.
Do you have any "solid" trans or engine mounts? If so, that can possibly creating vibration or vibration transfer.
Had vibration issues in my 67 GS400 convertible 4 spd and we have been going through the process of elimination. After having the alignment upgraded plus re-balance on the new radials it helped some. Then took driveshaft to a specialist and he said it was junk being originally made as a two piece so got a $500 new one. Then with car in neutral and all fan belts off went through RPM levels up to 3500 and vibration was definitely there starting at 2000 and increasing at 2400 and 3000. We then thought motor mounts? Put the car on a lift, took a look and bingo! We had a non- GS 400 mount on the drivers side that had different rubber cushion and design that resulted in metal on metal in one place. Replaced both mounts with correct NOS mounts I had purchased several years ago. Bottom line, vibration much reduced. Side bar: I installed boxed new control arms and sway bar on the rear and increased sway bar at the front to 1 1/8” which, with the re-alignment, new radials correctly balanced, the ‘wobble’ I was having before has virtually disappeared. Lots of time, money and energy but finally getting to a nice driver
i would check the engine and transmission mounts. under load the engine moves around much more than you think. even if your not hearing or feeling a clunk it may be moving enough to throw the angle off.
Some shops have tools to track down this sort of thing. Similar to: https://www.vehicleservicepros.com/...nc-thebis-noise-and-vibration-diagnostic-unit If stuck, it might be worth exploring.
Just some followup to this saga; I finally brought the car into a driveline rebuilder last week. Lo and behold; every bearing in the rear axle was worn out and one had literally come apart. So they're replacing all the bearings, so far it looks like the gears and the clutch packs are fine. They're currently sourcing the driveshaft issues, they think it might have something to do with the fact that the crossmember wasn't bolted in and just riding on some rubber bushings. I should hear what they've decided on Monday. They haven't figured out if or how many U-joints or if the cardon joints are any good yet, they're trying to source the cause of the vibration first. It's going to be a hefty bill but at least when this is over I should have a car that's quieter and glides smoothly at highway speeds. I just won't be able to put gas into it for a while...
So... the driveshaft issues were sourced today. It seems that the front driveshaft is pretty much shot. The front cardon joint is a total mess, which is something I figured was happening but no one at the time would listen. They took it apart and the ball is just about totally disintegrated. They claim this has been going on a long, long time. I reminded them that they missed this 8 years ago when I first brought the car to them complaining of the same problem. So what they're going to do now is modify the design to a more modern joint, something that has off-the-shelf replacements, and they want to totally eliminate the ball and socket idea. Apparently the rest of the shaft as well as the steady bearing is good; - so far. I think they're looking at reworking it all too. I suggested getting a replacement kit from Cars, or someone, and they said there'd be no guarantee that it wouldn't come apart in 2 years because of the condition of the ball. So altogether the whole job is costing me over $2K; hopefully it'll be vibration free after that. Tried to source another driveshaft only to find out the local salvage yard that I used to frequent went and crushed anything older than 1980 a couple of years ago. So there went about two dozen 60s vintage Buicks, and about 30 A-body Buicks, admittedly most of them were LeSabres or Specials. Still, there was a 66 Wildcat there that I was slowly bringing home in the form of parts. Now it's completely gone.
