How bad is the diff input shaft seal replacement?

[wkohler]

When I bought the car, the S3.25 was leaking quite badly, and I just discovered that the S3.46 I replaced it with is leaking as well.

I'm NOT going to buy another diff only to have the same problem, so what is SO bad about it that everyone recommends replacing the diff.

I only want to hear from people with experience on this, by the way - and yes, I'd rather pay someone the cost of a differential to do it.

[Kyle in NO]

The reason people recommend replacing the diff is two fold. One, the input shaft seal usually only starts dumping oil when the input shaft bearing wears enough to eat up the seal. Enough reason for me to replace it, as you'd have to disassemble the whole thing to replace the bearing. Second, if it has a crush sleeve under it, you have to tighten it just right when you reassemble it or you will ruin the damn thing. Another reason to make you not wanna mess with it.

I'd much rather swap the diff in about an hour than rebuild the damn thing! Once someone messes with it, its often never the same. I'd rather a dry one that has done 100k without issues than a freshly dicked-with one. FWIW, its not too often you see the input seal leaking on these diffs, I'd guess the input shaft bearing is getting too much play...

[Pat]

Ive seen some 2 year old BMW diffs leak at the pinion seal. When i do them, i use an impact gun. Just take the lock plate off,(get a new one) blast the nut off and pull out the flange. Remove and replaced the seal, then i put the nut on, blast it on with the impact gun and as soon as i hear it stop, i let off. Havent had any problems doing it that way. I think its worth a try before getting another diff.

Some people will take the lock plate off, use a punch and mark a spot on the nut, and then mark that same spot on the shaft. Replace the seal and tighten the nut just past the mark. I prefere the first method tho.

[wkohler]

I think it's a waste of a perfectly good differential to simply throw it away when the seal goes bad. Also, when we put this diff in, it was perfectly dry and has very low miles (well had). I think it's a waste to keep throwing differentials away. My mechanic says it's no problem and he's got a way to do it where tightening the nut isn't a big deal. He suggests replacing the seal. I talked to him to get his opinion, since everything I've read in the archives makes it out to be some serious thing. I figured he would rather not mess with it, but he said it's one whole helluva lot less expensive to replace the seal and he's never seen a diff go bad as a result.

I'm not letting a $10 part get the best of me.

Piece of shit.

[tsmall07]

You could definitely have someone do it for the cost of a new diff, if not less. It isn't as bad to do as people make it out to be. The only hard part is resetting the pinion depth and that isn't bad if you have a good bearing puller. There are shims behind the bearing on the pinion shaft and its just a matter of getting the right gear pattern with the correct amount of shims. You won't have to reset the carrier shims as long as you mark them when (if) you have to remove them.

Definitely replace the bearing while you're doing it.

[alpinewhite]

For what it's worth Chris, my mechanic did mine on my e32 s3.64 when he swapped the input flange over a year ago, and it's fine.

[LA]

It is entirely a matter of how much of a mechanical purist you choose to be Chris.


What Kyle said about the crush sleeve is correct. If you do not replace it there is absolutely NO WAY to have the correct preload on the pinion bearing. The physical deformation of the cylindrical part is what imparts the preload on the pinion bearing; once deformed, the yield strength of the material has been exceeded. Another way to say it is that the elastic limit has been exceeded - it is equivalent to stretching a spring too far so that it will not return to its original length. There is no way any mechanic anywhere can reuse the sleeve and have the correct bearing preload other than by pure chance. It is just physics.

That being said, there is a fairly large tolerance on what constitutes an acceptable pinion bearing preload in my opinion. And along those lines...what Pat said is also correct. Personally I use a punch and mark a spot on the nut, and then mark that same spot on the shaft, then go about two degrees past it upon reinstallation. It will work like a charm, I promise.

BUT...BUT - your pinion bearing preload WILL NOT be correct based on BMW specifications!!!

BTW - I have only been bold enough to do the pinion seal replacement on BMW diffs as discussed here. I've done Ford & Chevy diffs completely and what Tyler said is right on! Hats of to him for getting in there & doing it the old fashioned way by reading the tooth contact pattern.

[LA]

I just bumped so Chris could enjoy my articulate & insightful advicearoo one more time!

[wkohler]

We have decided to move forward with the pinion seal replacearoo. The only thing holding up the process is that the knowledge is on a cruise, so it will commence upon the returnaroo.

[LA]

We have decided to move forward with the pinion seal replacearoo. The only thing holding up the process is that the knowledge is on a cruise, so it will commence upon the returnaroo.

That is what I was afraid of. Some people just have no respect for maintaining the original condition (yes, right down to pinion bearing preload specification) of a perfectily good BMW. 8)

[Bimmerguy2002]

We have decided to move forward with the pinion seal replacearoo. The only thing holding up the process is that the knowledge is on a cruise, so it will commence upon the returnaroo.

That is what I was afraid of. Some people just have no respect for maintaining the original condition (yes, right down to pinion bearing preload specification) of a perfectily good BMW. 8)

My car is all original 8)

[LA]

We have decided to move forward with the pinion seal replacearoo. The only thing holding up the process is that the knowledge is on a cruise, so it will commence upon the returnaroo.

That is what I was afraid of. Some people just have no respect for maintaining the original condition (yes, right down to pinion bearing preload specification) of a perfectily good BMW. 8)

My car is all original 8)

Damn right! That's my story too, and as they say, I'm sticking to it.

Be sure to keep an eye on those clutch & brake foot pedal pads. There is a minimum tread depth wear spec you sure do not want to exceed!

[ismellfish2]

As a side note, you probably shouldn't scrap a diff, even if it's whining or leaking. Al Taylor had a contact who was buying diffs for 200 a pop, bad or good, and rebuilding them. This was on the east coast, so maybe not helpful for you, but just keep that in mind. I found out about this after I tipped one into the recycling bin at the dump, and I was pissed.

[Mike W.]

We have decided to move forward with the pinion seal replacearoo. The only thing holding up the process is that the knowledge is on a cruise, so it will commence upon the returnaroo.

That is what I was afraid of. Some people just have no respect for maintaining the original condition (yes, right down to pinion bearing preload specification) of a perfectily good BMW. 8)

My car is all original 8)

Yeah, mine too. Well at least the roof, and probably a couple other things. But I'd have to think about it to remember which ones

[wkohler]

We have decided to move forward with the pinion seal replacearoo. The only thing holding up the process is that the knowledge is on a cruise, so it will commence upon the returnaroo.

That is what I was afraid of. Some people just have no respect for maintaining the original condition (yes, right down to pinion bearing preload specification) of a perfectily good BMW. 8)

No, see the method he has incorporates none of the methods mentioned in this thread, thus far. It's something that he learned from another shop owner (for whom he used to work and I've known since I was born) and has worked exceedingly well.

[LA]

We have decided to move forward with the pinion seal replacearoo. The only thing holding up the process is that the knowledge is on a cruise, so it will commence upon the returnaroo.

That is what I was afraid of. Some people just have no respect for maintaining the original condition (yes, right down to pinion bearing preload specification) of a perfectily good BMW. 8)

No, see the method he has incorporates none of the methods mentioned in this thread, thus far. It's something that he learned from another shop owner (for whom he used to work and I've known since I was born) and has worked exceedingly well.

"... It's something that he learned from another shop owner ...''???

I grew up in a little town hot rodding my '67 mustang. Went to AU to get an engineering degree so I could design cars. Aerespace industry was offering about 40% more for starters. I'm a whore. End of story.

Now Chris, If you really knew any knowledgeable shop owners (even for the last two weeks) why would you be asking for help from the likes of the my e28.com board?

I think you just can not admit that even you, master of searching the archives, at times needs good advicearoo!

[wkohler]

I hadn't spoken with him and simply assumed it would be a job he wouldn't do. I searched and found many people advising just throwing the diff away. I asked what was so bad about it - not, that the seal is leaking, what should I do?