Rear Differential/Axle Leak

[Finnegan]

I was under the car yesterday and noticed this (see photos). The first area is on the passenger side by the differential where the axle connects to the diff. The second is a bit further up on the passenger side and on what I believe is the gas tank (it does not smell like petrol and is more lubricant-like). There are no drips or anything of that nature on my garage floor and no odd sounds (compared to Skelekitty's car). Nothing like this under hers which is clean as a whistle. The driver's side axle/diff shows something similar as well, but not as pronounced.

My major worry is that the reason things are not dripping is because there is nothing left to drip which would not bode well for the lifespan of the diff. I guess I could remove the top fill hole and check for fluid (no idea on the procedure there ).

The car is still under warranty, so it's off to the dealer with it I guess. I have a good SA and shop, but I'd like some opinions on what I'm seeing here and a recommended course of action from those who are more mechanically/technically savvy than I am before doing so. Good dealer or not you never know what it will be like the next visit, and I would prefer to be prepared/knowledgeable before going.

Any thoughts, ideas, advice, recommendations or you guys can offer?

[O-cha]

These go bad all the time, they aren't even that bad on your car yet, you have not lost any measurable oil yet.

[Finnegan]

Thanks O-Cha! I will cross worrying off my list and get on to my next issue: crab grass ! (Ah, life in the burbs...)

[trsbmw]

I had the same type of leak on the input flange side of the diff. Took it to the dealer, the seal was replaced. I picked the car up, there was a bad vibration introduced at 65 mph. The driveshaft was replaced next. The vibration was still there. Next BMW secondary support recommended the entire differential be replaced. Done, and problem solved, with a new differential at 10k miles...

[Finnegan]

Originally Posted by trsbmw

I had the same type of leak on the input flange side of the diff. Took it to the dealer, the seal was replaced. I picked the car up, there was a bad vibration introduced at 65 mph. The driveshaft was replaced next. The vibration was still there. Next BMW secondary support recommended the entire differential be replaced. Done, and problem solved, with a new differential at 10k miles...

Wow. I'm going to hope it's a one time fix, but I'm prepared now in case it's not.

[Finnegan]

Update: Pinon seal is bad. Being replaced under warranty. Hopefully I'll get the car back tomorrow (parts are due to have arrived 30 minutes ago).

[O-cha]

Originally Posted by Finnegan

Update: Pinon seal is bad. Being replaced under warranty. Hopefully I'll get the car back tomorrow (parts are due to have arrived 30 minutes ago).

50$ says they put it back together wrong, changing that seal means essentially rebuilding the diff.

[Finnegan]

Not going to take that bet O-Cha. You're right over 95% of the time.

So will the problems that result from putting it back together wrong be obvious? How about potentially hazardous? I have a track day coming up--I don't want the diff locking up at high speed or anything "fun" like that.

Hmm, if it's essentially re-building the diff then I'd guess there's a break-in required and fluid change at 1,200. Looks like no track day in that case.

Anything you can add would be appreciated.

[O-cha]

Originally Posted by Finnegan

Not going to take that bet O-Cha. You're right over 95% of the time.

So will the problems that result from putting it back together wrong be obvious? How about potentially hazardous? I have a track day coming up--I don't want the diff locking up at high speed or anything "fun" like that.

Hmm, if it's essentially re-building the diff then I'd guess there's a break-in required and fluid change at 1,200. Looks like no track day in that case.

Anything you can add would be appreciated.

No, no additional break in, what I mean by rebuild is things like preload will have to be reset. Most (nearly all) of the dealer mechanics if faced with a diff issue just replace the whole diff, they don't know how to actually rebuild it. I believe there is a "cheater" way to do it by marking the nut and reinstalling it in exactly the same place so you might get lucky. But... it's the dealership... so who knows.

PS the oil you noted on the axles IS the axle seals, but the larger amount you noted behind the heat shield is indeed the drive shaft seal, pretty much every single one leaks from the factory, this could also be CV joint grease though and not diff fluid, as this gets spun out as well if the simple paper seal is no good.

[Finnegan]

Thank O-Cha. That information is very helpful and appreciated!

I'll make sure I ask them about all the seals and the preload. I'll just have to see how it pans out--worst case I guess I end up with a new diff which isn't the end of the world.

[Finnegan]

Well, the update from the dealer is that the whole thing is buttoned back up and functioning correctly. We shall see, and I'll go over the parts list with them tomorrow when I pick it up. My car was kind enough to have a headlight fail while it was at the dealership, so that was replaced (bulb, controller...ballast?) while she was in. (I'll have to thank her for her good timing.)

[inTgr8r]

Here's hoping they got it right for you.

[Finnegan]

Originally Posted by inTgr8r

Here's hoping they got it right for you.

Thanks! Like I said, worst case it's a new diff, but having it done right the first time would be a major plus.

[Finnegan]

Okay, I have the car back and I can't find any issues. Pinon and axle seals replaced, car seems fine at low and high speed. Let's just say I tried it at a "range" of speeds and on corners.... I'll get to see how it feels at the track next Monday.

Other things completed while it was there:

Flaw in clear plastic on top of shift knob--knob replaced under warranty.
Headlight control module--replaced under warranty (note in file that if bulb goes it's covered too).
Engine mount bolts, sway bars, and other suspension parts checked (no issues). ARB and suspension torque checked.
Car came back without a spec of dirt or grease inside (and was not washed per instructions).

I think I've got a pretty good dealer/shop. I also think the assorted 12 packs of beer (Sam Adam's sampler this time, Sierra Nevada last time) I leave in the back of the car for the techs and my SA don't hurt either!

[Finnegan]

Update: Tracked the car w/o issue in the wet and dry, no issues, car feels solid and diff is working as it should.

[330indy]

Originally Posted by O-cha

..... but the larger amount you noted behind the heat shield is indeed the drive shaft seal, pretty much every single one leaks from the factory....

Can you explain why this is so? if this came with a flaw from the factory, or an assembly defect... Will it just do it again with a seal replacement. IOW, a diff. design characteristic, or.... other?
thanks for any insight.

[330indy]

Originally Posted by trsbmw

I had the same type of leak on the input flange side of the diff. Took it to the dealer, the seal was replaced. I picked the car up, there was a bad vibration introduced at 65 mph. The driveshaft was replaced next. The vibration was still there. Next BMW secondary support recommended the entire differential be replaced. Done, and problem solved, with a new differential at 10k miles...

Does anyone else see this as ridiculous for a needed diff replacement at this mileage interval??

[trsbmw]

Originally Posted by 330indy

Does anyone else see this as ridiculous for a needed diff replacement at this mileage interval??

Yes, I thought it was ridiculous too. It was certainly the last option, and at least they replaced it without a fight.

[Finnegan]

Clearly not all service departments have the same level of skills and capabilities. Like O-Cha said, it's tricky to get this work done correctly. It's not a paint by numbers thing, and that's all most techs are capable of. This takes real mechanical skill. So yes, it is ridiculous, but not terribly unexpected given the record most dealer shops have for repairs. I base that that on what I've seen on the forum when something, like VANOS bolts or anything mechanically complicated, goes wrong.