Cause of differential bearing failure?

HERMAN MONSTER

MEMBER
1997 FORD F-150
V8
2WD
AUTOMATIC
198,000 MILES

I took my pickup to the garage 6000 miles ago because of rear end noise. The mechanics found the spider gears badly worn so they put in new ones and new clutch packs and new bearings in the differential. The mechanic said the reason for the spider gears and clutches and bearings to be bad was due to lots of miles on the truck. Sounded logical to me.
So now six thousand miles later it starts making this howling or wining noise again so I took it back to the same garage and they took it apart and found the new bearings all scored and they said the fluid smelled burnt.
Both of the outer axel bearings are ok.
What could be the possible causes for this bearing failure in the differential? Please let me know as soon as you can or if you need any other information I will try to provide anything else you may need to make a diagnosis.
Thank you very much.

2 Replies

MHPAUTOS

MECHANIC
31,937 POSTS

Hi there,

Diffs fail for a number of reasons, worn out, lack of lubrication, abuse and incorrect adjustment when assembled to name a few. Diffs are fairly specialised devices and LSD units more so. The pre load on the carrier bearings must be set exactly with in makers specs. And the back lash on the pinion is even more critical, if your diff had not been "set up" correctly this could easily cause it to fail sooner rather than later, a skilled tradesman will be able to identify the tooth contact pattern on the crown wheel and pinion, this will be a good indication as to the initial set up, carrier bearings that are to tight or to loose will fail prematurely as well, it is just a matter of looking for the signs that will indicate why it has failed.

I hope that this helps.

Mark (mhpautos)