Hello,

So a few weeks ago I undertook a rear axle rebuild. Water had gotten into the axle somehow and has been like that for a long time. Lots of corrosion and bad bearings caused some pretty loud noise. Anyway, I followed the FSM pretty damn closely and replaced all of the axle bearings. The noise went away, but now there is a fairly loud whine/whirring when coasting.

I'm fairly certain the pinion preload was set correctly since we got 18 in-lb of rotating torque on the pinion that was required (needed 15-30). The backlash was within spec and the gear pattern looked correct. I didn't replace any of the gears, just the bearings and races. Coasting in neutral does not stop the noise. It sounds like an engine dying down.

What else could be causing this? Maybe I missed something?

I have a 1998 XJ 4.0 Auto 4x4, 8.25 rear end.
Rear U-Joints are new as well.

 

Did you locktite the pinion nut? Wouldn't be the first one to just come loose. Aside from that, pinion depth is the other fly in the ointment.

 

This is common with reusing gears. Once they wear in they don't like being moved. Do you have pictures of the tooth contact pattern on both the drive and coast sides?

 

I don't think so. I'll try to tighten it up but in worried about messing with the bearing preload. I supposed I have plenty of room for adjustment since I set it near the minimum.

If I adjust it, do I have to redo the backlash?

 

I don't, but they looked like what the FSM wants for good gear pattern.

 

Tightening up the pinion nut a little more did the trick!

 

imo, especially if you did not use a new pinion nut, its important to mark its relative position and use loctite

had one work loose once, that was before I found out most pinion nuts are designed to slightly deform the threads and are really supposed to be single use