Rear Suspension Problem

[HIZNHRZ]

I was recently standing behind my 91 ZR1 looking at the back end I noticed it is not sitting level. When parked on a level surface the passenger side of the car sits higher than the drivers side. From a side view, the space between the top of the rear passenger tire and the bottom of the rear fender is more than an inch higher than the same space on the drivers side.

Has anyone had a similar problem or seen this before?

The car has never been hit. The rubber bushings on each rear suspension piece are all original but appear to be in decent shape. Even if they were each dry rotted and distorted I can’t believe this would cause the car to sit an inch higher on one side than the other. The one thing I find suspect is the composite leaf spring.

How do you determine if the spring has gotten weak?

If I start taking anything apart, I’m thinking about replacing the rubber suspension bushings. Any suggestions whether I should use factory replacement rubber or polyurethane? Also, if I have to replace the spring, any thoughts or suggestions on replacing with a stock or aftermarket piece?

[tomtom72]

I remember going thru that w/my C3....I think it's a fairly common issue with the transverse leaf spring set up at the rear, both sides not being level.

I know I evened it out on my 72 after a few trial & retrials.....using the nuts on the spring bolts &* going up or down to get the bumper height even L to R. My Z is slightly off, I gotta stare at it for a while, maybe 1/2" or less. Jacking it up , stands under the frame, jack the spring end w/a puck on the jack pad and soft wook block up against the spring to unload it so you can move the nut, let her down, go drive around, re-measure & if not good repeat....just too tedious so I say lower it at the same time w/longer bolts and new bushings so it's worth all the trouble...

I think you're right about the spring bushings being shot, or close to being shot...MHO it's age as well as miles....I'm not a fan of poly, as I think for street use the car is stiff enough although the spring bushings might not make a difference if they were changed to poly with respect to stiffness/harshness. I know when I redo all my bushings I'll use mostly stock stuff as I'm not unhappy with the results that they give in my car. Maybe some Heim-jointed sway bar end links and maybe poly rack & swaybar mounts would be something I'd seriously consider, but the rest would proly be OE type stuff.


Tom

[Aurora40]

I believe a lot of C4's have this problem. Mine is now reasonably close to even, but if you look at the spring bolts one is all the way tightened up, the other all the way at the end of the bolt.

[HIZNHRZ]

Originally Posted by Aurora40

I believe a lot of C4's have this problem.

I'm hearing this a lot. The stock bolt, I think, is 14mm X 225mm which is roughly .5" X 9". The lowing bolts are 10". If the passenger side of my car is 1" high with stock bolts, the lowering bolts provide an inch of lengthr, and an inch longer bolt lowers the car ~1 inch, it would indicate I need lowering bolts just to get the car level!

Does this seem right to you?

Also, if the castle nuts on the leaf spring adjusting bolts are in a different position relative to the end of the bolt, will it affect handling?

[flyin ryan]

Originally Posted by HIZNHRZ

Also, if the castle nuts on the leaf spring adjusting bolts are in a different position relative to the end of the bolt, will it affect handling?

the side you have cranked up will essentially be stiffer. if you will be able to actually notice a differance is open for debate.

[HIZNHRZ]

Originally Posted by flyin ryan

the side you have cranked up will essentially be stiffer. if you will be able to actually notice a differance is open for debate.

Thanks for the response. I'm not concerned about feeling it as much as the car being unpredictable or dangerous. When I think one nut is going to be over an inch lower (over a 10" bolt) than the other, it just seems there must be somewhere else to make up the difference.

It could be come a little unpredictable over certain terrain. But I would not worry about it, as I doubt you would pushing the car hard enough to have it happen.


And the bolt has a hole in it for the cotter pin to lock the castle nut. It was never designed for adjustment.

[Aurora40]

Originally Posted by HIZNHRZ

Thanks for the response. I'm not concerned about feeling it as much as the car being unpredictable or dangerous. When I think one nut is going to be over an inch lower (over a 10" bolt) than the other, it just seems there must be somewhere else to make up the difference.

I'd think it would be worse to have the ride height on one side of the car 1" different from the other?

[Aurora40]

Originally Posted by flyin ryan

the side you have cranked up will essentially be stiffer. if you will be able to actually notice a differance is open for debate.

I'm not sure that is true? The spring should have a linear spring rate, so wherever it ends up shouldn't make it stiffer.

That's interesting if the stock bolt only has one cotter hole? The FSM has a section on ride height, I wonder how they say to adjust it if you can't move the castle nut through a very wide range?

Scott, what do you mean by first level it, then lower it? If you lower it you will have to adjust the stuff again to re-level it. If you plan on going to lowering bolts, leveling it with the stock ones first would seem to just be time wasted.

Originally Posted by Aurora40

I'm not sure that is true? The spring should have a linear spring rate, so wherever it ends up shouldn't make it stiffer.

Just like any other spring, you change the angle or induce more tension, it has less room to travel.

That's interesting if the stock bolt only has one cotter hole? The FSM has a section on ride height, I wonder how they say to adjust it if you can't move the castle nut through a very wide range?

You have roughly maybe 5mm of adjustment with the castlel nut and cotter pin.