Shaft seals for differential

[lxrubin]

I'm going to be changing out the pinion and output shaft seals on a differential soon. I have a couple questions so that I wont have to repeat the job.

1. I know that I need to lubricate the inner surface of the seal, but what about the outer to aid installation?

2. Should I use some of the gear oil to lubricate the seals or a different grease? I know that oil deteriorates normal rubber, so does that mean that shaft seals would be made of silicone rubber?

3. I have some silicone (non-petroleum) grease. Should I use this to lubricate the seals?

 

[jegs]

You don't need to lubricate the outer to aid installation. Use gear oil to lubricate the seal surface.

 

[Trav]

Use regular grease on the inside of the seal surface where it rides on the shaft.
New seal materials are resistant to almost all greases and fluids found in automotive apps.

Normally you don't need anything on the outside but if the housing got nicked you can use a very thin coat Indian Head gasket shellac. When i doubt use it.

Indian Head is a Permatex product and can be found at any parts store for a couple of bucks.

 

[Kestas]

Some seals come pregreased. If not, use the parent lube that the differential uses. It's not the type of lube that is important, but rather the fact that the seal is not installed dry.

Don't use silicone, because I've seen cases with Krytox where there is a bad reaction with differential fluid.

 

[mechtech2]

I never want to see a job twice. I use a THIN coating of silicone RTV around the outer seal edge.
Just use the gear oil on the inner lips and yoke sealing surface.

IMPORTANT!:
MARK the pinion nut and yoke [their relationship]! Use a punch or small chisel.
This is the only way to tighten it again and be at where you were before [preload wise]!
[Unless you tear down every part and set the tooth contact and preloads.]

 

[Zaedock]

Originally Posted By: mechtech2
I never want to see a job twice. I use a THIN coating of silicone RTV around the outer seal edge.
Just use the gear oil on the inner lips and yoke sealing surface.


This is what I do. Never had an issue or complaint.

 

[lxrubin]

Thanks all! so grease the shaft surface and leave the outer dry or apply some RTV if I'm slightly worried.

 

[lxrubin]

The only thing I'm concerned about the rtv is cleaning it out afterwards. I don't want to have to use a razor or abrasive material afterwards to remove it if a leak occurs in the future.

 

[Kestas]

I'm not sure if it's clear in this thread. I believe the rtv is suggested for the bore mount surface of the seal body, where it is pressed into the cavity. This is known among seals people as the "anchor" surface. There is typically a green or blue coating called "boretite" applied to this seal surface.

I don't see how this is a concern for cleaning it out in the future.

 

[lxrubin]

When dissasembling the differential, I noticed that there is significant scoring on the output shaft's bore at the sealing area. This is a spare diff, and I will have to see what the diff in the car looks like. Any of you experts have seen this sort of wear? I'm assuming its not advisable to reuse these shafts.

Sorry for the huge picture. I'll have to figure out how to make these smaller. Notice the "crack" liiking line about half an inch on the shiny bore from the flange area.

 

[mechtech2]

That doesn't look like any differential part I have ever seen.
More like a stubshaft that goes into a transaxle.
What are you talking about when you say pinion and output seals?
I have no idea.
If wear is too much, either adjust the position of the seal to ride on a good part [if you can], or get a 'Speedy Sleeve' repair kit.
It slips a new surface on the worn part [use sealant], and a new special seal with a different seal internal diameter is used.

 

[lxrubin]

Originally Posted By: mechtech2
That doesn't look like any differential part I have ever seen.
More like a stubshaft that goes into a transaxle.
What are you talking about when you say pinion and output seals?
I have no idea.
If wear is too much, either adjust the position of the seal to ride on a good part [if you can], or get a 'Speedy Sleeve' repair kit.
It slips a new surface on the worn part [use sealant], and a new special seal with a different seal internal diameter is used.


This is a stub shaft on a rear differential for a 91-99 BMW 3 series. I was speaking of the pinion shaft and output shafts (stub axles) seals, but haven't looked at the condition of the pinion shaft yet.

That's a good idea to have the seal ride on a different part of the shaft. I think I may have a few mm of wiggle room.