Hello all, looking for ideas as I am out of them....

Suspension set-up: (everything new in the last 100 miles)
Front: Hotchkis springs and sway bar KYB shocks
Rear: Hotchkis 1.5 drop leafs, sway bar, KYB shocks
Car has Hotchkis subframe connectors and front chassis brace bars.

I recently replaced the subframe bushings and x measured the car from the front leaf spring mount to the opposite lower ball joint zerk fitting (within 1/4 inch) just to verify the alignment holes. Wheelbase is 108 RH, 108.25 LH. Car has been on the alignment rack twice.

Here's the issue:
When you accelerate hard off the line the car is pretty stable, if you don't powershift, there is a wiggle from the rear (to the left) on the shift (all shifts). Once you finally let off there is a big (scary) wiggle to the left from the rear end. There also seems to be alot of vibration in the car at 55-60 MPH.(wheels and tires new and balanced)

I never drove the car with the old suspension in it, I have triple checked all bushings (which were tightened at ride height on the lift) used a crowbar to try and get something to move, sent it to the alignment rack twice. It feels like a dirt bike with loose back spokes when it happens. I am going to reach out to Hotchkis next, but any ideas?

 

Family,

Not much left to check, there. I would suspect the driveshaft is not balanced for speed, but those "extra" problems are not typical. I would check the motor/transmission mounts, and the mounting points for the rear axle/jackpot. You may have two or more issues working in combination to make your symptoms happen. I suspect you have a broken bolt in the powertrain mounts somewhere. You may also need to spin-balance the driveshaft, but that job is not expensive. You can check the spin-balance of the driveshaft easily, on a frame lift. Best wishes.

 

Driveshaft was also my first thought.

 

It can be a pain to track an issue like this down after a project is done. The builder would have tried to hide any damage the car took if he did not realize the problem it could cause.

The way you measured the car for alignment it is not the best way and I would not be happy with the 1/4". Normally I laugh at people that pay for a 4 wheel alignment on these cars vs a front wheel alignment but in your case it may be a good idea. You have a car that is built well beyond what GM made and the 4 wheel alignment will pick up any looseness or anything bent front and back. Besides you're going to want to be sure everything can be brought back to stock setting plus have a little wiggle room for tweaking setting the more you learn the car.

I used to do trouble shooting for suspension problems at a dealer back in the day. One time I had a car repaired in our body shop then sent over for alignment. I could tell it was bad just pulling on to the lift. I could not get the wheels to track with any amount of adjustment. I used a cross measurement from the factory gage points and found a 1/2" error. I then checked riding height at several position. Turned out the car was shaped like a banana front to back and side to side. It had to go to the frame machine and was on there for 2 days and they ended up repainting it cause of the stress pulls you could see in the doors and so the body panels could be re-gapped.

Your vibration is another story. Yes the stress on the tire could cause a vibration but I think you have an opportunity here. There is a whole science behind tracking down vibration. I think doing it in a DYI setting would be really informative. The main tool needed everyone has. Its your phone. This will take some research on your side but I can give you the basics. Vibration equals harmonic as long as you don't have several different issues at the same harmonic vibrations should be easy to track down what part or a least would system is causing the vibration. You will need a vibration analyzing app for your phone. The app will let you see the vibrations, it will look something like a heart beat monitor plotted across time. I you only have one issue you should see a peak and that peak will have a repeatable distance on the plot (again just like a heart beat) that distance you want to convert to a cycle. Then I would convert those cycles to cycles per minute. You also should know all the ratios of your trans and rear and tire diameter. Now with a GPS (don't trust your speedo) see if there is a correlation between RPMs of various components and the vibration cycles per minute.
I would suggest using a spread sheet. Now if the the vibration is a stress vibration the Cycles may not match the the RPM exactly but they should follow the same plotted line. Think a HP curve, the RPMs of what is causing the vibration may be a function of 1/2 the cycles. As you can imagine the cycles of a drive shaft will look very different then a tire.

You can use this process to track down just about any minor vibration. Even like a miss manufacture alternator just by calculating how fast it is tuning. GM trains its tech in this process, back in the day we used a Reed tachometer. There are professional versions of this software for your phone if you search the app store.

Edit: My arm chair diagnoses make me think this is more of an alignment issue. The vibration I defined as a "stress vibration" is the tires fighting the road. Since your sticky tires are not going the way they want to they will jump instead of chirp like a stock tire would. I would defiantly be sure the tires are in alignment before doing the vibration tests. The only real thing the vibration analysis could do for you is rule out the drive shaft as a possible issue. It is a great tool for verifying drive shaft balance and drive line angles are correct.

 

Just watched your recent video. I would not have expected all the stuff you found. Car looks like what we use to call a body-man's restoration. If it looks right it is right. I know you upgraded it but all those parts that where on there before where not cheap. Then just to have so much just put together wrong or not check.

 

I FOUND IT!! Found the drivers axle tube rotating in the center section! The plug welds popped out. No fluid leaking. I think the rear sway bar masked the problem by holding it in and returning it to its correct position. The video is crazy of the insane +pinion angle and RH leaf spring wrap while LH spring doesn't move. Thanks all for your input. I will have the YouTube channel video up once we get it welded up and drive it.

 

I know its crazy, like he wasnt a car guy and didnt know what he was doing....

 

Are the brakes causing the steering wheel vibration? What about the driveshaft? Is the rear end in good shape? Motor Mounts?
It seems you have done your fue diligence on the car so the setup is plum, but what if the car isn't plum? I have heard many times how quality control was out of control back in the day on the assembly line. Born on the wrong day.
I mean your knowledge of your car's setup is your advantage. But some cars were built just a little bit wrong at the factory. Some have been wrecked and put back together so they look right; but aren't.
I belive you have to check the drive line. It sucks troubleshooting these things. Sorry I don't have a quick answer. You probably know what is going on with the cars engine and trans, but I would troubleshoot the driveline; and make sure the rotors aren't roached, which can cause steering wheel vibration, along with what the twist is doing to the driveline when accelerating. Something has to be moving wrong...maybe the rear end is causing one wheel to spin before the other, throwing it all off when accelerating.

I am trying to help. Thats all. Good luck.

 

That is a new one on me and I thought I have seen it all.

 

Had a feeling it was driveline. I can count on one hand how many people I know that have the dimensions of their suspension!
Not to mention the relation that the two ends have on each other.
Glad you found the axle slippin'.

-Chris