do u have to re-shim the rearend on a diff change?

Yes. Manufacturing tolerances between the different posi units could be enough to throw off your rear end. You may luck out and have them stay the same, but you'll never know unless you have a dial indicator to check backlash.

At least check it.
Then you will know that all is well.

I did have to re shim my rear when I put in the Auburn unit.

jason

90lxcoupe said:

does the differential have to be re shimmed and the backlash reset if i am not changing gears and just putting in a new posi unit and axles?

thanks

Click to expand...

if going from ford to ford , probably not if going from ford to a eaton or auburn then probably so ......check it with a dial to make sure , dont just guess

I went from my stock trac-loc to an eaton posi with 31 spline axles. Didn't need to reshim anything. Been working well since then.

I went from the factory ford T-lock to a Torsen but with a FMS gearset - all the specs changed, especially pinion depth.

I did the same thing on my rear end (put a Truetrac LSD in my Dana rear end). We checked backlash before loosening anything -- it was within factory spec. Then we set the shims up on the new diff exactly like they were on the open diff we removed. We lucked out -- it went in, and the backlash was exactly as it was with the previous diff.

But -- you need to measure, and be prepared to re-shim because it may be necessary.