A differential question

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.

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.

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.

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

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.

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

I will check that. Thanks!

Usually 2 things will take a seal out.

#1. The seal just gets old and loses it's elasticity and wears a grove in the shaft and it's starts to leak.

#2. The bearing get too much side play from bearing slop and it starts to wallow the seal out and it leaks.

If the seal is bad I give the bearing a hard look before I just replace the seal.

Given that the axle was recently over-hauled I would suspect the seal lip was nicked by the axle shaft splines at install, this is the most likely cause I've seen for seal damage. Other potential is that the seal lip had a defect when the seal was manufactured (there is a certain amount of seal damage that occurs in manufacturing, depending on what level of inspection the seal supplier uses some of them get through).

I inspected the axle vent and it's in perfect working order. The hose was probably replaced when they overhauled the differential as it looks brand new. Also, it's a little wet around the pinion seal. I suspect that's weeping a bit..and for now I just don't care. It had synthetic oil in it. I know on my old Harley EVOs I was told time and again not to use synthetic fluids in the older, pre-twin cam, engines as it would cause leaks. Now I'm running dino 80-90 in the differential. I'm going to monitor it over the next months and see how it goes. I hate replacing a pinion seal and, I hate paying someone to do what I can do but, don't want to do. It's a quandry. My plan is to pay off my wife's van and replace the old suburban anyway. Besides, adding gear oil is quick and easy (and cheap).

put a dry seal on a dry shaft and see how long it lasts, lube the seal during install and it will be happy