billschroeder5842

It's Sunday morning so I'm already studying you FSM on today's project; adjusting the rear ride height on my '91 ZR1.

I was waxing (yes, I DO wax along with spinning as many of the wrenches as I can) my 89 yesterday when I noticed the gap between the rear tires and wheel well on the ZR1. Being distracted (and giving my arm a break) I pulled out my tape measure and found that my fronts were even but the drivers side rear was about 3/4-1 inch lower with the driver side dipping.

I crawled around and noticed that the castle nut on the spring bolt was "higher" on the driver side by about 3/4 of and inch. The passenger side nut sat even with the hole in the bolt the both with the cotter pin going thrown the castles (is that a word??) in the nut and locking it in place. The drivers side had the nut sitting above the cotter pin/hole and was just "floating" on the spring bolt withe cotter pin just flopping about.

I always get confused with rear springs---is it "tightening or raising" the nut on the bolt will lower the car while loosening (putting downward pressure) on the spring will raise it? I've only had two cups of coffee...

The FSM (Pages 3D-9 for those with a 91) tells of the process but not the specs- just "align with hole and cotter pin."

So it looks like I'll put the car on jack stands, put the floor jack under the spring and raise slightly to take pressure off, loosen/lower the nut until it aligns with the bolt hole and pop the cotter pin in the hole/lock in the castles? Is it that easy? I'm kind of a factory spec kind of guy so I'd just like both sides even to factory tolerances. I just drive; no racing for me.

Is that it? Any tips or tricks?

whalepirot

Only one cuppa, so far.

Longer bolt= lower car. It's that easy, but R alignment may need slight adjustment.
Ah, refill time!

billschroeder5842

So, To even it out, I'll need to take the driver side and raise/tighten the bolt (spinning it up the shaft) on the driver side or loosening (lower than the cotter pin) on the passenger side?

Huh... I would have thought that I'd just align both pin holes and I'd be good? This rear must be REALLY out of align as there would be about 1 1/2 inch of difference in the nut/bolt height??

WVZR-1

How long are your bolts? Mentioning they're cotter keyed hints OE but you might check. I'd think you want to have equal length, run the car over some "rumble strips" on the side of most highways and then recheck height BUT you need to remember that trim height ain't measured using quarter lip to anywhere.

Trim heights are suspension fixed points to a flat surface. There is a reference rocker to flat surface also. Before you do a thing I'd suggest checking trim heights using the FSM.

See maybe 3-21 or so in the FSM

92ragtop

If you have a difference of 1 1/2 ", something else may need attention.

And, if you don't use the cotter key, you must use a Nylox nut so it does not undo.

383vett

...or two nuts tightened against each other.

ctmccloskey

I had a similar issue on my 88 Coupe and there was nothing wrong with the rear end parts. I had replaced virtually every component in my rear end to get rid it of some play I had found at 80,000 miles.

My final solution was to use a four foot mason's level stretched across the width of the car and then I adjusted the nuts to make the car as level as it could be. This has worked for several years with no further complications.

Has someone removed or done any serious work on the rear end of your car? People that work on rear ends like to use new hardware and sometimes that means the "wrong" hardware. Could it be a sign of a worn out shock or the spring getting tired?

Good Luck on getting your car set up properly! Sometimes being a "perfectionist" can bite you in the rear... No pun intended!!

billschroeder5842

Well, I got the car on a level surface and put it up on jack stand. I verified that the side to side (measured from the jack point) are within 1mm.

I loosened up the driver side and tightened up the passenger side. They were about 1.6 cm off. I measure height from a common location on the spring, and adjusted up/down until then are the same.

Does this sound right- the FSM is pretty vague? I need to take it out for a spin and let it settle but what a PITA to jack it up, put wheels back on to take it around the block before I'll (inevitability) have to make more tweaks.

Anything I need to check before dropping? I'm better a beer now...

BTW, I'll need a twin nut on the driver side as it is below the cotter pin hole.

ddahlgren

Pull the shock and if ok pull the spring. I am betting it delaminated or something is very broken in the rear. Is the car new to you or just happened to finally notice it? Corvette owners generally give their car a good look over fairly often to miss it for a year.

billschroeder5842

Well, that was a waste of time; I clearly don't know what I'm doing.

I kept good notes of each adjustment, with measurements before and after. I drove a couple of blocks after each tweak so as to let the suspension settle. I loosened and tightened each side nut and and had multiple combinations, moving the nut at least an inch up one side and again down. I could not seem to make a difference or figure a pattern from the measurement taken from the rear wheel well:

Start Driver 67.3, 67.5, 69.7, 69.8, 71.0, 69.8, 70.0, 69.7, 70.0, 70.0
Start Pass 68.3, 68.5, 71.3, 71.5, 71.6, 71.2, 71.8, 71.3, 71,5, 71.9
-1.0, -1.0, -1.6, -1.7, -1.6, -1.4, -1.8, -1.6, -1.5, -1.9

Where I left it was.... the lower spring was DEAD NUTS on for each side with the same measure point exactly the same from the ground and the nuts were exactly the same (thread count) on the bolt. The passenger side was exactly where I started and the drivers side nut is about 3/4 of an inch lower on the bolt. The measurement from the jack point was 7mm lower from the driver side to the passenger and the measurement from the wheel well was 1.9 lower on the driver side than the passenger side.

So, I made it worse? Where do I go from here?

Thanks!

C409

..... When you are done messing around , it would be a good idea to have the wheels aligned .....

ddahlgren

If the spring is a bunch stiffer on the right front it will transfer weight to the left rear. It is what they do on nascar types that only turn left. At this point I would bring it to someone that knows what they are doing and if they had a set of wheel scales it might be enlightening. You might check for bound up sway bars as well acting like springs when they should not be doing that.

GREGGPENN

Sounds like you did it backwards (and that you might not be able to correct the problem w/o a new rear spring anyway).

As was posted by WhalePirate (post#2), longer bolts lower the ride height. Because the DS was already TIGHTENED more than the stock setting AND that you are drooping on the LR, someone had already attempted to compensate.

Some people completely remove the rear spring (which isn't that hard) and rotate it 180-deg. Basically, you're putting the stiffer side under the side your butt is compressing every time you drive it. The question is whether it would be sitting closer to level -- with you in it AND the spring reversed? The question is also whether enough "spring" is lost than you just don't have enough left in the DS of the rear spring to get up up to level. (Consider you have to be even LOWER when you are sitting in the car...and over the LR wheel!)

Mine was off by 1/2" to 3/4". I added stainless washers to the DS rear spring bolt -- to effectively shorten it (which is where you were when the castle nut was spun further up the bolt!) In my case, the back end evened out...and could be explained by years of more compression on the DS (from driver's weight).

Because someone already shortened that DS up a bit, AND because you are further off (than I was), you'd need to really crank that DS nut up higher OR add washers (above/below) the rubber keepers on that bolt.

If you are anywhere near the 210 lbs that I weight, I think you should seriously consider rotating the rear spring 180-deg. Then -- at the factory castle-nut positions AND you sitting in the car -- see how close to come to level. I'm guessing you'll be happier than you are now.

Or...buy a new spring.

GREGGPENN

Obviously, an even better approach!

383vett

There is no need to put the car up on jack stands to adjust the nuts on the lower bolts. You can easily crawl underneath and using a box end wrench, hold the upper bolt head while cranking the lower nut. As mentioned, use a nylock nut or two nuts tightened against each other. Move the nut higher on the bolt to raise the car and lower it too lower the car. You don't even have to drive the thing.

ElisTwoCents

This here

New long 11" bolts (stocks are 9") are available on eBay IIRC where I got mine

billschroeder5842

Thanks- good advice.

I have it going to the local Corvette Guru on Thursday. I explained the situation and he is confident.

All I want is stock specs; nothing fancy.

I will suggest (ask?) about the spring pivot 180 degrees. He might have a few thoughts.

HAD2HAV2

Bill, here are a couple of shots of the extended spring bolts. I had the driver side being too low compared to the other side. One day when I rip the rear suspension out I will 180 the spring.




Driver side



Passenger side


Now the ride height is very closely even.

billschroeder5842

Thanks H2H2, did this adjustment lower the overall height of the back end or just even it out?

How "off" were the side height to begin with and what is the distance between the nuts on the bolts-- it looks like about 1 1/2 inches?

HAD2HAV2

1.5 inches is spot on. I raised one side and lowered the other to get both sides almost even, within a 0.5 inch.