Differential Backlash/Preload measurement

[M3_Ken]

Does anybody know where to measure to get the correct backlash between the lsd spider gear? I recently purchased a used diff to rebuild since mine has been clunking for a long time now. (Had the car in the air and spun the wheels to confirm diff is the problem) I plan on measuring the shim instead of using the racingdiffs fix. I am assuming you are looking at the backlash between the spider side gears and place the dial indicator on the spider gear tooth but want to confirm. Thanks

By the way what happened to M3forum?

[maupineda]

.06 - .1 mm

[maupineda]

Did not note you asked about spider gear. But I would aim for .1 to .12mm

[sapote]

.06 - .1 mm

This is more like spec for pinon/ring gear backlash, not spiders to side-gear.

[sapote]

I recently purchased a used diff to rebuild since mine has been clunking for a long time now. (Had the car in the air and spun the wheels to confirm diff is the problem)

This backlash on the output shaft is not the reason for the clunk, because all diff have this amount of backlash including the non-M opened diff.
The clunk is caused when the old LSD clutch stack suddenly slip causing the spiders to hammer on the side gear which on the shorter output flange.
However you can reduce the clunk noise by reducing the spider/side gear. I.e. jack wheel off gnd and gently rotate it end to end and measure the plays on the tire circumference, and let's say it's 3", then I would add flat shims on the side gear (which one? to the shorter output flange side gear) to reduce the wheel plays to 0.5" when rocking it back/forth.

[M3_Ken]

Thank you the spider play was what I was referring to. I took the rear cover off and noticed the spider gears smacking each other when the axle flange is spun. I’ll take it apart and order some shims to take some play out.