Shake at 60MPH

[81CutlassDsl]

My 85 Cutlass 2 door has developed a shake at 60mph+. It had new tires put on it and the problem actually got worse. So to try to rule the tires out i switched them with the other car. Ruled out being the tires.

This shake seems to be in the floor and not in the steering wheel. The car has air shocks and weak springs in the back end. Could this cause of it? Adjusting air pressure in the air shocks can either make the shake better or worse. It's better at lower pressures but still there. The tires have a whine to them, but on this car it has a whine accompanied by something that sounds like it's hopping... almost like a wheel hop. This problem is worse on smooth roads.

I also changed out the U-Joints and had the drive shaft balance checked.

Clueless at this point and almost ready to give up on this car.

Any suggestions for rear springs that don't sag quite as bad? Both of them are due.

 

[JBreu]

You might have an issue with the stall converter.try tightening up all the bolts on the transmission, converter and the flywheel....Are you sure the shaft was balanced? Hopefully not on a Monday or Friday??

 

[megaladon6]

jack up the front end and shake it down. my guess is a loose/bad bearing.
also check the rear control arms for slop. you usually want to do this with the car on the ground/suspension loaded.

 

[454muscle]

I suggest re-checking the drive shaft as I had the same problem with my GP, and also consider a warped wheel. Even though it may be balanced on the machine, it could still be warped and cause shaking.

 

[username]

You said that it had weak springs in the rear,have you changed any spring rates on the car? If the front and back spring rates are to close together you can get harmonic pitching, more than likely its not this just throwing out additional ideas besides the obvious ones. Whats the last thing that was done or happened prior to the shakeing starting? Check engine and trans. mounts, driveshaft might be out of balance,do you have adjustable upper rear control arms? (pinion angle)

 

[pontiacgp]

If a drive shaft is causing a vibration the vibration is there constantly and does not suddenly appear at certain speeds.

 

[81CutlassDsl]

This car is completely stock 85 cutlass. 3.8 liter and 200 metric trans. The rear springs are factory original along with the front. I had my rims and tires from my 81 on this car and the problem was still there.

Front wheel bearings are tight and replaced after this problem started. Ball joints are tight. Steering is tight as that was all gone over. Engine and Transmission mounts were checked.

The car has had transmission shifting problems from 2nd to 3rd for 10 years now. But it has never caused the car to shake. Engine is so underpowered that the transmission can't make up it's mind what gear it wants to be in at 25-30mph. Could something have finally went?

This seems to be coming from the back of the car as nothing is felt in the steering wheel.

Getting tired of throwing money at this car as i've spent more than what it's worth trying to find this. Might start using it for parts for the 81.

 

[pontiacgp]

have you checked the pinion bearing and the rear yoke?

 

[jae]

have you checked the pinion bearing and the rear yoke?

I agree. If the front end is tight, wheels/tires ruled out, rear springs are gone and your compensating for that with the air shocks I'd start looking at the rear end. Something is worn, either bearing or yoke and your pinion angle may be way off or bushing slop in the upper and/or lower arms like the others said.

Also, if it's been driven for 10 years with a bad 2 - 3 shift that may be your problem. Is it just shifting in / out of 3rd or does it "clunk" into 3rd? Internal problems could be sending a vibration through the driveline at higher speed and make it appear it's wheel-hop, and those weak shocks aren't helping. But most GMs shift at that point, between 25 - 35mph.