Stability Problem

[Thomas F.]

My 69 Corvette (big block 4 speed) started acting funny recently. It acts like something is wrong in the rear end. It seems to have a mind of it's on by steering to the right and/or left without me turning the steering wheel. This activity scares me and I am afraid to drive the car. I have been under the car and examined everything I can see and all seems tight and secure. It has the aftermarket one piece fiberglass spring. There is no leakage from the shocks. Wheel bearings seem to be ok. Tires seem to be good with plenty of air. Everything underneath the car seems to be tight and all the parts are there. The car appears safe to drive but something is wrong. I don't won't to start taking the car apart to check stuff. I want to check the simple things first. Any ideas or advice would be appreciated. Thanks

[Leif A.]

Re: Stability Problem

Have you checked to see if your trailing arm shims are still in place?

[Gene T.]

Re: Stability Problem

It might be the rear end clutch discs are slipping and a simple way to correct is to change the rear end fluid. Be sure and add a bottle of positive traction fluid which is obtained from your local GM dealer parts dept

[David H.]

Re: Stability Problem

Thomas

How many miles on your car?

Dave


Movement of axles?

https://www.youtube.com/watch?v=oesqUzCejxM

https://www.youtube.com/watch?v=_Dh2zId7BbY

Google search topics: "rear differential play corvette tires move"

[Michael H.]

Re: Stability Problem

Have the trailing arm bushing been changed ? I had the same problem on my 67 and the bushings were shoot, it allowed the trailing arm to move forward and backwards.

Mike

[David M.]

Re: Stability Problem

For your safety its time to get it up on the lift.

Look at all the chassis wear items front and rear. All bushings, BJs, control arms, struts, hubs, axles, axle in/out play and the spring perch etc...

True story: My buddies 68 Tri-Power twisted the spring perch right out of the frame. He reported a weird wandering feeling a day of two prior. This was circa 1982 so young and dumb was a factor. It wasn't a pretty site. It was major surgery to repair it. It didnt damage the body. It wasnt rusty either. If that happened at speed it would have been worse.

[Duke W.]

Re: Stability Problem

IRS Corvettes are very sensitive to rear toe. I had a recent experience with a friend's '67 L-71. A quick flick of the wheel to the left caused the rear to step out. Measurements showed slight toe-in on the left rear and actual toe-out on the right side, which explained the problem. We ended up swapping three 1/32" shims from the inboard to the outboard side of the RH trailing arm to achieve a slight amount of toe-in. With the bias ply tires the handling is still a bit "spooky", but response to a quick flick of the steering wheel either way yields the same dynamic response.

This car has only 15K miles and it appears that the problem has existed since the car left St. Louis. Maybe that's one reason why it has such low miles.

You need to check that the rear trailing arm shim packs are intact and the trailing arm bolt is properly torqued. This should be done with the car at normal ride height, so a drive on lift is best. You can also measure total toe to get an idea if it's within specs, but that won't tell you if toe is equally distributed between both sides, which is important. Does your car have the long cotter pin through the frame and shims?

While it's on the drive on lift check all other bolt torques associated with the rear suspension and axle included wheel bolt torque. The AIM is a good reference to see how the axle and rear suspension are assembled with torque values for all fasteners.

Also jack up the rear and check wheel bearing clearance and axle side yoke end play. Check wheel bearing clearance by grabbing the top and bottom of the tire and wiggle. You should feel very slight play. Then grab the front and back of the tire and push it in and out. You can get an idea of side yoke end play by having a helper observe the yoke and estimate movement. A new, properly assembled axle should have no more than about .010" side yoke play.

The next step is to get it on a four wheel alignment rack.

If the shim packs are intact and the bolt is properly torqued, the next suspect is a deteriorated trailing arm bushing.

What tires are installed?

Duke

[George J.]

Re: Stability Problem

Thomas, you said you have checked everything under the car, but did you check to see that the wheel lug nuts were all tight. I had the same thing happen when someone didn't tighten them correctly. Also, check the mounting bolts for the front A-arms. I have had one of them come loose, and the steering started wandering.

George

[Gary G.]

Re: Stability Problem

I had a similar issue on my 1972. It turned out to be the inner left ujoint. it had semi froze up. Replaced all 4 and the steering returned to normal. I had no issues with clunking or other common sounds.

[James G.]

Re: Stability Problem

IRS Corvettes are very sensitive to rear toe. I had a recent experience with a friend's '67 L-71. A quick flick of the wheel to the left caused the rear to step out. Measurements showed slight toe-in on the left rear and actual toe-out on the right side, which explained the problem. We ended up swapping three 1/32" shims from the inboard to the outboard side of the RH trailing arm to achieve a slight amount of toe-in. With the bias ply tires the handling is still a bit "spooky", but response to a quick flick of the steering wheel either way yields the same dynamic response.

This car has only 15K miles and it appears that the problem has existed since the car left St. Louis. Maybe that's one reason why it has such low miles.

You need to check that the rear trailing arm shim packs are intact and the trailing arm bolt is properly torqued. This should be done with the car at normal ride height, so a drive on lift is best. You can also measure total toe to get an idea if it's within specs, but that won't tell you if toe is equally distributed between both sides, which is important. Does your car have the long cotter pin through the frame and shims?

While it's on the drive on lift check all other bolt torques associated with the rear suspension and axle included wheel bolt torque. The AIM is a good reference to see how the axle and rear suspension are assembled with torque values for all fasteners.

Also jack up the rear and check wheel bearing clearance and axle side yoke end play. Check wheel bearing clearance by grabbing the top and bottom of the tire and wiggle. You should feel very slight play. Then grab the front and back of the tire and push it in and out. You can get an idea of side yoke end play by having a helper observe the yoke and estimate movement. A new, properly assembled axle should have no more than about .010" side yoke play.

The next step is to get it on a four wheel alignment rack.

If the shim packs are intact and the bolt is properly torqued, the next suspect is a deteriorated trailing arm bushing.

What tires are installed?

Duke

The ''MASTER'' has spoken. Thank you Duke for sharing all your knowledge.

[Duke W.]

Re: Stability Problem

Thanks for the kind words, Jim! Now all we need is for the OP to get back to us with answers to my questions.

Duke

[Tom B.]

Re: Stability Problem

I'm with Duke....I have seen many independent rear suspension cars that if the toe in is off they will be all over the road.