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...:mrgreen:

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.

:thumbsup:
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]

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]

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]

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.

[Jeffvette]

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.

[HIZNHRZ]

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

I agree and the bolts you buy for lowering don't appear to have a cotter pin either. So if this bolt wasn't designed for adjustment, how do I first level the car and then lower it? Please help!

[Aurora40]

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.

[Aurora40]

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?

[Jeffvette]

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.

[flyin ryan]

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.

if your cranking pre-load into one side enough to raise the ride height, well...i'm sorry it's going to be stiffer by a bit. it's an I.R.S., if it was a solid rear axle, that's a different story, transverse or not. my Stingray in my avatar, i had it 60' a best of 1.325 seconds with the factory I.R.S. with out a trans. brake. my world revolved around I.R.S. stuff for ten+ years. in the I.R.S ¼mile drag world i'm considered an authority by many. didn't make them happy when i put a solid axle set-up in:cool::sign10:. just trying to provide correct information:dontknow::cheers:.

[HIZNHRZ]

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.

I'm not yet convinced that I don't have a problem. I understand that many ZR1's may not sit level but are they more than an 1" off? More than an inch is a whole lot!

What I'm planning to do is level two cinder blocks on my garage floor. I was then going to jack the rear wheels onto the cinder blocks and take some measurements to the floor. I'm hoping to figure out "what" is out. I figured I'd do this with the factory bolts. I don't have the "lowering" bolts yet. It doesn't appear I'm going to be able to find them locally.

Has anyone seen the rear end out of level by over an 1"?!?!?!?

[HIZNHRZ]

Yes I know the measurements are very course but they do allow one to visualize the problem. The pictures are on a car with ~10K miles that until recently was a stock garage queen. The spring "adjustment" bolts are stock and the castle nut and cotter pin is in the same place on both.

Drivers side:
http://i62.photobucket.com/albums/h113/hiznhrz/IMG_2325-1.jpg
Passenger side:
http://i62.photobucket.com/albums/h113/hiznhrz/IMG_2326-1.jpg

[Aurora40]

Just like any other spring, you change the angle or induce more tension, it has less room to travel.
Presumably though the spring has enough travel for the whole range of suspension movement?

While I realize lowering/raising affects the suspension geometry, well he's trying to make them even. If the ride heights are the same but the spring bolts are not, does it matter?

Won't the spring rate still be the same on each side, meaning it will take X amount of lbs of force to compress the spring/suspension an inch (where X is the springs rated rate). If you tighten the nut up, you aren't compressing the spring more, rather it will raise up the car by the same amount, correct? So it's not getting pre-compressed or anything? Or am I thinking about it wrong?

Also, is it correct to say the spring raises the car from the middle (more or less), which is possibly why side-to-side it can have some variation?

[Aurora40]

Yes I know the measurements are very course but they do allow one to visualize the problem. The pictures are on a car with ~10K miles that until recently was a stock garage queen. The spring "adjustment" bolts are stock and the castle nut and cotter pin is in the same place on both.

Scott, you may want to look in the FSM. Ride height is not measured in terms of wheelwell gap. You should measure out the appropriate place on the side skirt and measure to the ground.

[Jeffvette]

You can not take measurements there.

Proper measurements are taken from the frame rail to the ground. As body panels are not always applied or installed in the same position.

[HIZNHRZ]

You can not take measurements there.

Proper measurements are taken from the frame rail to the ground. As body panels are not always applied or installed in the same position.

I realize the measurements are not the correct way to diagnose
"a problem". I guess I am doing a poor job of providing information that might allow one to visualize the issue.

If it were your car and when it was sitting on a level surface the space above the rear tire on the passenger side was one inch greater than the same space on the drivers side, what would you do?

Thanks in advance.

[Jeffvette]

Has the rear sway bar been off this car at all?

How did it look before you swapped the wheel/tire combo?


If it were your car and when it was sitting on a level surface the space above the rear tire on the passenger side was one inch greater than the same space on the drivers side, what would you do?

Coilovers :D

[HIZNHRZ]

Has the rear sway bar been off this car at all?

How did it look before you swapped the wheel/tire combo?

I'm not positive the sway bar has been off but Marc Haibeck just put 4:10 gears in it if that tells us anything. Are you thinking it might be flipped 180?

I never really noticed the problem with the 17 inch Amolds and Michelins or with the sawblades and GYs. I'm in the process of pulling out some old pictures to compare.

[HIZNHRZ]

Scott, you may want to look in the FSM. Ride height is not measured in terms of wheelwell gap. You should measure out the appropriate place on the side skirt and measure to the ground.

Bob, I know there are trim dimensions in the FSM but darn if I can find them. Do you know what section they are in?

[Jeffvette]

I'm not positive the sway bar has been off but Marc Haibeck just put 4:10 gears in it if that tells us anything. Are you thinking it might be flipped 180?

Just for giggles, look in the rear wheel well and see which way the sway bar bends for the last section. You can do it with the car on the ground.

[HIZNHRZ]

Just for giggles, look in the rear wheel well and see which way the sway bar bends for the last section. You can do it with the car on the ground.

The stabilizer shaft bends up to connect to the shaft link.:mrgreen:

[Jeffvette]

The stabilizer shaft bends up to connect to the shaft link.:mrgreen:


So that would be correct. Let me mull it over tonight.

http://www.pnwzr1.net/Jeff/Coilover/IMG_5420.JPG

[HIZNHRZ]

So that would be correct. Let me mull it over tonight.

Thanks Jeff, very much appreciate the help. Look forward to hearing what you come up with.

[Aurora40]

Bob, I know there are trim dimensions in the FSM but darn if I can find them. Do you know what section they are in?
In my FSM it is on page 3-15, though it just refers to diagrams that are on page 3-21 and 3-22.

[HIZNHRZ]

In my FSM it is on page 3-15, though it just refers to diagrams that are on page 3-21 and 3-22.

Thanks Bob, I actually did find the info last night. There is also some good info in 10-3-3.