A differential question

fj12ryder wrote:
Generally speaking a seal won't start leaking for no reason. How old is the vehicle? A new seal leaking may be a sign of poor assembly, or bad part. The other causes of a leaking seal may be poor sealing surface, i.e. surface groove, rough surface. Excessive out-of-round shaft movement can also cause seal failure. If the vehicle has sat for a time, the seal could dry out and not conform to the shaft surface. And a seal can just fail over time due to heat cycles too.

The whole differential was overhauled by a good (and expensive) shop a year ago. The bearing looked perfect as did the mating surface of the half axle. The seal didn't show any signs of heat or splitting. The fluid looked great, the rear end runs silent and no signs of wear anywhere. I didn't see any obvious location where the seal failed but, the rotor/parking brake drum was pretty well oil soaked. I cleaned the rotor and installed a new parking brake shoe along with the new axle seal. I kinda got the feeling that it MAY have been leaking from where the seal meets the differential shaft housing. By looking at where the seal meets the axle shaft I could find no obvious place where fluid was coming out. For all I know it could have had a very slow leak since it was overhauled last year and I just discovered that the parking brake wouldn't hold on a hill.

We have two trips in the next two weeks. I'll keep an eye on it and pull that rotor when we get back home.

Make sure the rear differential breather is not plugged, if it is pressure will build up and force fluid past a seal.

As long as the bearing was good I would not worry. Check the fluid level. Often the level should be 1/2" below the fill port but many shops top it off level with the port.

Generally speaking a seal won't start leaking for no reason. How old is the vehicle? A new seal leaking may be a sign of poor assembly, or bad part. The other causes of a leaking seal may be poor sealing surface, i.e. surface groove, rough surface. Excessive out-of-round shaft movement can also cause seal failure. If the vehicle has sat for a time, the seal could dry out and not conform to the shaft surface. And a seal can just fail over time due to heat cycles too.

It can (happens a lot on the front of big MH's) but it's not likely on the back. It would have to of lost a heck of a lot of oil and if that happened, the other side would be toast and the bearings would be noisy.
I wouldn't worry about it.