Rear A-arm shims - transplanting parts

[EricH]

I know about carefully noticing the number and location of the shims whenever I take the A-arm off and put it back.

But suppose I'm replacing the A-arm outright, with either a new one or a transplant from another car? How do I decide how to shim the new one? Just use the old shim arrangement on the theory that the shims are intended to handle car-to-car variation in the positioning of the mounts on the chassis, while the A-arms are likely to be pretty much the same?

 

[Jimbro1000]

The shims are intended for correcting small imperfections in the alignment of the mounting points, not the arm itself so yes you need to retain the old arrangement of shims as you had already guessed at.

 

[EricH]

OK, so I screwed up and lost the shim positions



Now what?

 

[Steve Hoelscher]

Actually, the shims are used to account for the difference in manfacturing tolerances in both the a-arm and the mounting points. I have found that both have a noticable variation in tolerance.

I have written a detailed proceedure for shimming the control arms. However, it was some time ago and on the old Xweb forum. You may be able to find it there using the search function. If not, let me know and I can re-post it.

Basically, fit the arm at normal ride height without shims, center the position of each end as close as possible, then fill the gaps with shims.

 

[EricH]

SteveH, you are GOOD

This is the post you meant?
http://www.network54.com/Forum/12159/message/978663192/Toe+and+Shims

Many thanks

 

[Steve Hoelscher]

This is the post you meant?
http://www.network54.com/Forum/12159/message/978663192/Toe+and+Shims

That's it.

Glad to help.

 

[htfx19]

What if it is not adjusted correctly?

Hi Steve.
As you may guess, I didn't pay a hellovelot attention to adjusting the A-arm. I sure didn't baby the shims or replaced them 100% right.
Isn't all that compensated for by aligning the rear wheels on a wheel aligning machine?

 

[Steve Hoelscher]

Hi Steve.
As you may guess, I didn't pay a hellovelot attention to adjusting the A-arm. I sure didn't baby the shims or replaced them 100% right.
Isn't all that compensated for by aligning the rear wheels on a wheel aligning machine?

Hi Herzel,

Actually, alignment has little to do with the shims. The purpose of the shims isn't wheel alignment but rather the previoulsy mentioned manufacturing variances. Proper shimming of the a-arm ensures the a-arm has proper range of motion without binding and/or fouling the mounts. It also prevents the chassis mounts from deforming when the bolts are torqued and the a-arm bushings and chassis mounts from gauling from movement.

There is a small effect on wheelbase and toe but its minimal. Toe should always be checked and reset after any suspension work that would affect the settings.