Im thinking of changing from a FE1 rear spring to a NYU on my 89 and was wondering what the correct shim sequence and thicknesses are. I've read that they differ for each spring code but have not found a listing of the different combinations. This will give me basically a 92 Z07 spring setup but with a 3 N/mm stiffer front spring (93.1 vs 90.1) to compliment my 32/24 sway bar setup. Thanks for the info if you have it!

 

..... The shim combination is less important than getting the spring held in nice and snug without being too tight ... the cast aluminum L-Shaped spring mounting brackets are fragile and will break if you use too many shims .........

 

I have read that about being fragile. I still need to know the correct amount and combination top/bottom so it's is installed correctly. Too loose would be an issue also.

 

The FSM doesn't refer to springs by code, they're done by "color" code on the spring. An FE7 rear could be a "green" or "yellow" code on a coupe and the spacer packs are different:

A yellow spring calls for 1.72mm above and 2-6.11mm below the spring. A green spring calls for a 1.72mm & a 6.11mm above the spring and a 6.11mm below the spring. I've got an NYU spring that's near new and might be that is "no color". I thought I had another but can't put my hands on it.

If your spring has a color code on it still then you could use that to determine. I've never paid attention to color code only the "letter" codes.

The thickness of the stack is important to provide proper fit of the "anchor". The FSM mentions not to add spacers to adjust trim height.

Less above the spring would be inclined to lower the trim height. Maybe let the angle of the half-shaft at ride height determine which arrangement you choose.

 

Oh dear. I was hoping there was a definitive answer to this! I guess when I get a spring I will see if there is a color on it and go from there. Thanks for the input!

 

What?

who said that "shims" were a precision fitment? or a handling enhancement?

they are NOT.

The ONLY reason those shims are there is to properly HOLD the fragile aluminum bracket to/against the spring rubber mounting block so it is neither loose, nor bound too tight in which case the aluminum bracket just breaks...

Yes, there ARE suggested factory fitment specs, BUT that's assuming that everything is NEW, a GM product and is the factory SPEC at the time of installation....

you are NOT so lucky. In the case of "used" equipment, shims are just there to fill gaps. YOU have to figure out how many, where. Like it has been said, OVER or UNDER the spring makes a SLIGHT difference in ride height. Whatever the thickness of the shims are......

Shims are there to fill the gap, the extra space, IF ANY between spring pad and bracket. Same as the shims in your door frame in your home.

You bolt up your new spring with the brackets....ALONE. No, you CAN have friends there for support, I mean the bracket goes on by itself, THEN you see how much shimming gap there is to fill.
Visually check for looseness above or below the spring. Place 1 SHIM or 2, (they vary in thickness just like A-arm shims) to fill in that void, and create a SNUG fit between bracket and spring mounting block.

AGAIN.......

if there is TOO much of a BIND from improper shimming, the mounting bracket will simply crack and you will be done until you spend WEEKS trying to find a part that originally cost less than a cheeseburger. Plain, simple, no machining, cast aluminum piece.

The bracket should fit against the frame, with a snug grip ( squeezing the spring) against the spring rubber mounting block/pad, BUT the bracket MUST be completely against the frame...bottomed out.
IF there is GAP between bracket and frame, you screwed up somehow with TOO many shims and THIS is why common sense is necessary.

One More time...

DO NOT get the bracket in a bind and/or over tighten one side or the other. CRACK. The aluminum is VERY fragile in this part.
It really IS.

why all the drama I do not understand.

Did anybody call a meeting or get all bothered when they installed the front door? That got some shims. For the exact same reasons...to fill a void and hold the frame right.

 

I measured the thickness of the spring, and compared it to the replacement spring.
The value was off by a few thousandths or a paint layer or two.

I also waited until the spring was loaded before torquing the bolts

 

Thanks! Sounds like it was pretty much a straight pull and replace.