[SloopJohnB]

Seal material same, different sizes/part numbers.
Oil is very specific, from BMW $$$$ many argue, however the argument is price biased.

I don't know that the seal material is the same or even very quality-oriented given BMWs penchant for suppliers. I think the answer is complicated, and price is definitely an issue for BMW as well as the DIY or indy that sources the parts. It's not like you have a choice between viton or polybutylene or other materials and/or seal configuration...it's more than just ID/OD and width, spring loaded, etc. The flange seal surface is critical for longevity as well and you really can't control that. Stack up probably leads to as many seal failures but not as many as that little plugged vent! LOL.

 

[SloopJohnB]

It's the amount of play in the M3 differential vs the open diff on the other cars. Higher mileage ones have an egregious amount of play with the output shafts.

So you're saying the BF outside bearings on the M diff wear egregiously?

 

[MrMCar]

I don't know that the seal material is the same or even very quality-oriented given BMWs penchant for suppliers. I think the answer is complicated, and price is definitely an issue for BMW as well as the DIY or indy that sources the parts. It's not like you have a choice between viton or polybutylene or other materials and/or seal configuration...it's more than just ID/OD and width, spring loaded, etc. The flange seal surface is critical for longevity as well and you really can't control that. Stack up probably leads to as many seal failures but not as many as that little plugged vent! LOL.

 

[MrMCar]

So you're saying the BF outside bearings on the M diff wear egregiously?

From what I've seen, yes.
Typical 3rd. owner strolls in and talks about the common lower gear on/off throttle noise.
Up in the air I grab both rear tires (I'm 6'4" and have a large wingspan) and shake the tires fwd./aft rapidly.
I get the usual stacked tolerances noise of the bearings/driveshaft/guibbo rattle.
Grabbing the inner CV joints of the rear axles, it's not uncommon to have these wiggle quite a bit. It's just how they are after 100K.

 

[SloopJohnB]

From what I've seen, yes.
Typical 3rd. owner strolls in and talks about the common lower gear on/off throttle noise.
Up in the air I grab both rear tires (I'm 6'4" and have a large wingspan) and shake the tires fwd./aft rapidly.
I get the usual stacked tolerances noise of the bearings/driveshaft/guibbo rattle.
Grabbing the inner CV joints of the rear axles, it's not uncommon to have these wiggle quite a bit. It's just how they are after 100K.

Interesting. I have 113K miles and no on/off throttle noise. My indy (DINAN dealer, Fairfax Service, Fairfax VA) did mention the guibo should be replaced (and I had him do it) because it showed a lot of cracking. Maybe it was just karma but I felt the driveline was maybe a little more responsive afterwards..LOL. I've only had one wheel bearing issue in the last 55 years..on a 2000 Audi A6 with the 4.2L V8 at 130K miles. Sounded like an airplane roar, dang dealer couldn't hear it. I put the car on jack stands and in gear and I could clearly hear the RF wheel bearing noise. TOLD the dealer to change the bearing and yes, it was in visually poor shape. No other bearing problems. Used to be every time you changed brake rotors it was either clean and pack bearings or replace them....with modern sealed bearing hubs not so much!!!

 

[Sapote]

I get the usual stacked tolerances noise of the bearings/driveshaft/guibbo rattle.
Grabbing the inner CV joints of the rear axles, it's not uncommon to have these wiggle quite a bit. It's just how they are after 100K.

The stacked up plays from diff output shafts to the main drive shaft came from pinion/ring gear + spider gears. But this is not related to the seal leaking.
Ok, so the M3 output flanges (where they connected to the CV joints) have radial and axial plays. This excess plays is the main reason the seals are leaking. I don't think my 323iT or 325iT have this kind of plays at 170K miles and 130K miles, and this is why they don't leak. These seals cannot take radial and axial plays. Same as the crank seals: if the crank has radial or axial plays then the seals would leak very quick.

 

[MrMCar]

The stacked up plays from diff output shafts to the main drive shaft came from pinion/ring gear + spider gears. But this is not related to the seal leaking.
Ok, so the M3 output flanges (where they connected to the CV joints) have radial and axial plays. This excess plays is the main reason the seals are leaking. I don't think my 323iT or 325iT have this kind of plays at 170K miles and 130K miles, and this is why they don't leak. These seals cannot take radial and axial plays. Same as the crank seals: if the crank has radial or axial plays then the seals would leak very quick.

You're trying to cover 2 different areas of discussion with one dismissal.

I never said the stacked tolerances of the input was a cause of the leak.

The axial play does, when talking about the output.