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?

 

measure on both sides and see how far off it is. fairly common problem.

the spring could be off, but more likely the adjustment.

if the spring is cracked, replace it. I have a set of 95 ZR-1 springs if anyone needs them. I went coil over.

 

Ron, it seems like a 95 leaf spring should fit a 91; do you know for sure? How many miles on the car before the spring was replaced?

You refer to an adjustment. The only adjustment I can see is perhaps the spring bolt that holds the insulator and spring in place on each end of the leaf spring. Is that what you are thinking? If so, I appears the cotter pin pretty much determines where the nut is positioned. Do I need longer bolts and forget about the cotter pin? If the driver/passenger side adjustment on these bolts is not symmetrical, will it affect handling at high speed?

 

Scott,

I'm surprised this hasn't drawn more response through the day!

With the car on a known level surface measure all the heights to the quarters and hood using the centerline of the wheels. A state inspection lane is generally as close to level as you'll find if you know an inspector! Ideally you would like "similar" dimensions left & right. With the right rear appearing high the left front should be low in comparison to the right front. You could play with the adjustments of the spring bolts in the rear, ride it for a bit to "settle out" BUT if you can get it to a trim height your happy with duplicate it with proper hardware to locate it. Longer bolts and "prevailing torque" nuts. You can raise the nut on the factory bolt but it's not wise to lower the nut beyond the cotter key hole for anything but the "test"!

There's actual "trim" dimensions in the FSM that are used to "underbody" locations of the car and that's the accepted "standard" when measuring for handling and modifications. Check those and if they're on the button your fine. There's many out there with the same condition you've noticed. It's odd you've just picked up on it since the "wheel/tire" combination but now I'd say you're "looking"!!!!

Now before you do all of this "Find yourself some RUMBLE STRIPS" and as rough a road as your comfortable with and "shake-out" the suspension to let it find it's desired stance. How many miles since the tire/wheel swap?

 

A fairly common problem. Mine was off an inch right to left like yours. I used 2 longer bolts (lowering bolts) and leveled mine out while dropping it an inch in the back.

 

Seems like most Vettes I see are like this. I always assumed it was from the fact most Vettes are driven around without a passenger more often than not causing more sag on driver side. You might be able to adjust the bolts at the end of the spring to correct this. If you go with 10" long bolts you can lower and probably correct the rear ride height.

 

Dave, I've been looking for these ride height dimensions in my FSM but can't find them. What section are they in? I was planning on setting the rear end up on leveled blocks and taking measurements. I was looking for a "standard" to compare to.

I put the wheels and tires on last weekend and then drove to Ocean City. I had no problem on the way down but coming back I could hear the rear passenger tire rubbing (strangely enough). I wouldn't have throught the passenger side would have hit anything given it was the side that was raised. The funniy thing is the rubbing sound stopped in a gentle curve to the left and got worse in a curve to the right. When I pulled the tire, I couldn't see anywhere on the wheels or wheel well with rub marks.

Thank you very much for your help. You've given me a place to start.

 

Ittlfly, thanks for the response. The longer bolts, I'm told, are about 10". The stock bolts are about 9". So you were able to correct your car that was off level an inch AND lower it an inch also? This would be ideal. I'm thinking that it also means moving the castle bolt down an inch on the adjustment bolt has a greater than 1" change in the suspension ride height. Does this sound right to you?

Thanks again.

 

The trim heights should be in the diagnostic sections of steering/suspension/wheels in the 3 section of the FSM. There are also frame dimensions from a "datum" in the 10 section of the manual and you can use the same reference points and just use those points on a level floor to establish the relative height.

The information you want should be in two charts in the 3 section diagnostics just before the wheel alignment section.

You shouldn't require differences of 1" on the rear bolts to trim the car. You will likely use the majority of the inch each side to lower the rear to the height you want and mentioned earlier when you installed the wheel/tire combination a couple weeks ago.

If you would like 10" bolts and want to give it a go tomorrow 10/18 I work tomorrow in Tyson's and I'll carry a pair of 10" bolts and nyloc nuts to work with me!!!

 

Dave, You're the man! Many thanks. I'll see you tomorrow.