What to look for in used differentials?

[bmp]

Looking to buy used differentials and was curious what to look for when buying used ones. Wouldn't want to have it installed and find it starts humming after only 20,000 miles of use.

Thanks.

[Danny]

Make absolutely sure that they spin.

[Adrian_Visser]

make sure there is fluid in it






jk it may be hard to tell if the output shaft bearings humm unless the diff is in the car and spinning at speed under load.

[rThor432]

If it takes 20,000 miles for a diff to start making noise, there wouldnt be a problem when you bought it.

Best thing to do would be to pop the cover off and see what it looks like inside. You can check the backlash on the ring gear, but that's about it really. You wont get any noise out of the bearings without loading them up. If you do, dont buy that diff.

For limited slip units you could check the break-away torque of the different output shafts to check the condition of the clutches.

[Wh33lhop]

My diff whines :( I've heard that all the LSD units tend to whine. That doesn't make much sense to me but my buddy got his S4.10 rebuilt and his definitely whines (then again he has no sound deadening).

[rThor432]

My limited slip units dont whine.

[h82crash]

The LSD is not whining, the bearings or gears are. If it makes ANY hissing noise turned by hand, it will in the car. Grab both flanges and turn as fast as u can. Also should be silky smooth, no notchyness.

[Holland]

Cool, nice to know.