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Discussion Starter #1
2002 E46 M3 MT - 200k

I have a fresh gear oil on the back upper passenger side of the transmission where the polyurethane mount is. All gear oil toward the bottom of the differential is dry so it's drying from the heat as it leaks down from higher up on the diff.

I'm assuming it's the seal at the axle input shaft, but I haven't had much experience with differentials on these cars so I wanted to get some experienced input on this.

1. Can the Diff leak from anywhere else besides the axle input shaft areas, like maybe the front?

2. If it were leaking from the front, wouldn't it be more well dispersed on the diff as opposed to just one side and only showing wet in the back?

3. Can the axle seal be replaced without lowering or fully dropping the diff?

Thanks.

Brian C.
2002 BMW M3 6sp - 200k
 

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I'm in process of sealing my differential now.

Up front at input shaft there's only one seal/area that it could leak from. That's exactly what happened to mine but since I have it out I'm doing the output seals as well.
Mine was visible dripping from the bottom front, especially where the support brace is, it was always wet from gear oil
I've been too thinking of doing this without taking it off the car but at the end I got it out. I'm not sure whether or not you could do it on the car, there are some things that block your access.

Sent from my Nexus 6 using Tapatalk
 

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Discussion Starter #3
I'm in process of sealing my differential now.

Up front at input shaft there's only one seal/area that it could leak from. That's exactly what happened to mine but since I have it out I'm doing the output seals as well.
Mine was visible dripping from the bottom front, especially where the support brace is, it was always wet from gear oil
I've been too thinking of doing this without taking it off the car but at the end I got it out. I'm not sure whether or not you could do it on the car, there are some things that block your access.

Sent from my Nexus 6 using Tapatalk
Thanks for the input. Thankfully, it's not the front seal since you say that one's blocked by supports.

The side seals didn't look like they were blocked so I think I can change those with it in the car, but I wanted to be sure and ask you guys first.

Most of my mechanic experience is with a long history of old 5sp MT Taurus SHOs I used as track cars and daily drivers, so I've had very few cars with differentials.
 

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E30M3 Race F10 535 R1150Rt M Coupe
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There's an occasional issue with the E46 M3 differentials. I've also contacted the National BMW CCA Race tech to make him aware of.

The E46 M3 differential has a VERY SMALL vent hole attached to the upper part of the cover. We have come across (about 3 times) whereas the small hole becomes clogged with debris and the differential cannot vent properly.

There's usually a small amount of oil vapor present in the venting orifice. If you live in certain areas, this oil can attract dirt and eventually become clogged.
If it clogs completely, it can create a oil leak from the seals.

Like this:
Show up at the track and it's a cool day in the morning. The ambient temperature of the oil (car gets to the track on a trailer) in the differential is ~72°F.
You then go out on track (lets say the next to last session) and now the ambient is much higher and so is the oil in the differential owing to ambient and the clutches working hard, transferring heat into the oil.

This can create a positive pressure inside the differential. Which usually results in a leak.

We now have a new procedure when servicing M3 differentials:
We drain the oil. While both the fill and drain plugs are out, we take a blow gun with a vacuum hose attached to the end. Hold directly over the vent hole and blow it clean. At the same time placing a finger into one of the fill/drain holes to feel the incoming air. Now we know the vent hole is clear.

The above came about on 3 track HPDE cars that had a persistent leak that new seals (twice) did not resolve.
Clearing the vent hole solved the issue with all 3.
HTH?
 

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I should caution:

The above vent clearing must be done with just the right amount (not too much) pressure and BOTH the fill/drain plugs out.
Otherwise one could reposition and/or pop a seal out?
 

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Discussion Starter #6
There's an occasional issue with the E46 M3 differentials. I've also contacted the National BMW CCA Race tech to make him aware of.

The E46 M3 differential has a VERY SMALL vent hole attached to the upper part of the cover. We have come across (about 3 times) whereas the small hole becomes clogged with debris and the differential cannot vent properly.

There's usually a small amount of oil vapor present in the venting orifice. If you live in certain areas, this oil can attract dirt and eventually become clogged.
If it clogs completely, it can create a oil leak from the seals.

Like this:
Show up at the track and it's a cool day in the morning. The ambient temperature of the oil (car gets to the track on a trailer) in the differential is ~72°F.
You then go out on track (lets say the next to last session) and now the ambient is much higher and so is the oil in the differential owing to ambient and the clutches working hard, transferring heat into the oil.

This can create a positive pressure inside the differential. Which usually results in a leak.

We now have a new procedure when servicing M3 differentials:
We drain the oil. While both the fill and drain plugs are out, we take a blow gun with a vacuum hose attached to the end. Hold directly over the vent hole and blow it clean. At the same time placing a finger into one of the fill/drain holes to feel the incoming air. Now we know the vent hole is clear.

The above came about on 3 track HPDE cars that had a persistent leak that new seals (twice) did not resolve.
Clearing the vent hole solved the issue with all 3.
HTH?
Thanks! That may well be where the leak is coming from since it's from the topside of the seal and top of diff as opposed to all around the seal.
 

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Discussion Starter #8
I should caution:

The above vent clearing must be done with just the right amount (not too much) pressure and BOTH the fill/drain plugs out.
Otherwise one could reposition and/or pop a seal out?
Can I reach the vent on top of the diff and blow it out without dropping the subframe or diff?
 

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Can I reach the vent on top of the diff and blow it out without dropping the subframe or diff?
I believe you could but only if you have a 90° angled adapter. I might be wrong though, since my trunk floor has a spare tire bubble and M3s don't.

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Discussion Starter #10
I believe you could but only if you have a 90° angled adapter. I might be wrong though, since my trunk floor has a spare tire bubble and M3s don't.

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Thanks, man.
 
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