Sweating M diff - severe?

S

Sae

Senior member
Hi guys, couldn't find anything direct from a forum search, so anyway, the car has just passed it's MOT - good news, however bad news is that they reported a sweaty diff as a cautionary.

They recommend having the pinion seal replaced, but just wanted to know if anyones else has a sweating diff or has had the pinion seal replaced? My car is an 07 plate and there are far older / higher mileage cars on here, so is it a big/tricky specialist job to replace or would you trust the dealers to do it?

Any experiences, feedback appreciated :thumbsup:
 
No. This sounds like a money maker for the shop. If it looks like it's "sweating" - it's not "leaking". The shop has no idea how bad it is - since the only way to tell would be to clean the area and drive the car many miles - then re-check.

It's likely the "leak" is so minor it's not worth fixing. If the sweating "residue" is from, say, the last 5 years...Whose to say the shop wouldn't "fix it" and you would have the exact same residue in 5 years?

The only way to really tell is to clean the area with Brake Kleen and keep an eye on it.
 
If it sweats, it leaks. Provided the oil didn't came from somewhere else (which is not very likely)
Clean it up, and if it sweats again fix it! And immediately check your diff oil level!
There's only 1 liter or so in the diff housing, and low oil in your diff is a certain way to ruin your diff really fast. (and I mean really fast, maybe even in a few miles, as it has a clutch lsd, so it gets hot too!)
The diff is a really expensive part ((1800gbp/$3000 or more).
The pinion seal is a known wear part for the z4m diff, so the shop is probably right.

If you let the seal be replaced, be sure you get a shop that knows what it's doing, as the tension on the pinion shaft is very ver y critical and that is not done by torque or so. It is done by carefully winding the nut back in exactly the same position, so it has to be marked.
If they f**k up they have to do a wear pattern analysis & adjustment (and that requires a really old guy that has knowledge from 'back in the days...' :lol: ).
 
I had a leaky diff sorted during the car's inspection 2 service at 45k. They replaced the seal. Had no issues since


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Did a spot check on my drive where it's parked and there does seem to be some faded oil spots under the rear axle. In anycase would like to get anything replaced before it becomes more serious.

So, as to the job of getting it replaced, I'm assuming that if I put it into a dealer they will have the rights tools etc to do the job correctly and will have some sort of warranty for the replacement, just a bit nervous getting anything slightly tricky done to the zed by anyone... :(
 
Cool, looking into it a bit more, it seems that this is a common wear and tear part, so shouldn't really have anything to worry about getting it replaced.

Feeling slightly less worried now :)
 
pinion seal is a known leaker on this car i can guarantee theirs lots of z4ms with this slowly weeping away and they aren't noticing. we will ALL have this at some point.
 
Beedub said:
pinion seal is a known leaker on this car i can guarantee theirs lots of z4ms with this slowly weeping away and they aren't noticing. we will ALL have this at some point.
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Cool, hadn't really seen any posts on this forum about it so wondered if I had a major issue.

Have just passed the 5yr ownership mark on a 7yo car, so just trying to keep an eye out for what other part failure/perishables to watch out for in the next year / x-K miles.
 
Sae said:
I'm assuming that if I put it into a dealer they will have the rights tools etc to do the job correctly and will have some sort of warranty for the replacement,
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A dealer will certainly have the proper tools and will probably follow the proper procedure as bmw intended as they probably follow the official workshop manuals. (and the procedure is in there)
Warranty I don't know. Ask.

But it's never a good thing to keep things leaking on a 350hp sportscar imho, so keep an eye on it.
 
GuidoK said:
But it's never a good thing to keep things leaking on a 350hp sportscar imho, so keep an eye on it.
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Completely agree with you on that, getting some repair quotes to get it replaced.
 
Also if it is sweating it will get worse and worse (as it is already worn, it will not stop, it will wear further).
So by not replacing it you only postpone the inevitable, but with risks.
 
Sae said:
GuidoK said:
But it's never a good thing to keep things leaking on a 350hp sportscar imho, so keep an eye on it.
Click to expand...

Completely agree with you on that, getting some repair quotes to get it replaced.
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Mine wasn't much to replace. The oil to re fill will probably cost more.... and you'd be as well changing the oil while you're there


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Adamski said:
Sae said:
GuidoK said:
But it's never a good thing to keep things leaking on a 350hp sportscar imho, so keep an eye on it.
Click to expand...

Completely agree with you on that, getting some repair quotes to get it replaced.
Click to expand...

Mine wasn't much to replace. The oil to re fill will probably cost more.... and you'd be as well changing the oil while you're there
Click to expand...

All sorted 200 squideroos + VAT, seal/gasket/liquids came to less than a third, they wanted to do the job including inspection/investigation rather than just replace the seal just because I asked, so as a precaution I agreed with. Will keep an eye open but fingers crossed that won't see any diff seal issues for another 5 yrs :)

You must have got a good deal Adam, or was that part of a general going over when you got your car?
 
Sae, yeah I when I got my car I put it into Eastern BMW and got a full health check done. It also needed some servicing items. The leaky diff was discovered, and fixed along with a few other niggles they found :thumbsup:
 
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