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      01-13-2019, 04:37 PM   #1

Drives: 2008 135i, 2011 328i xDrive
Join Date: Jan 2008
Location: Canada

iTrader: (2)

changing diff output shaft seal

I have a 3.46:1 diff with an M-Factory helical LSD, originally installed in 2015. In 2017 (20,000 km later) it suffered an internal bolt failure which was repaired under warranty. The replacement only has about 3000 km on it now but has been seeping oil from the RH output shaft seal, so I decided to replace it. Here i the process I followed:

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The oil seepage was slow but enough to foul up the rear subframe directly behind the diff. The above picture is after a thorough cleaning and a short drive.

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First step is to remove the bolts securing the half-shaft to the diff. Lucky for me the leak was on the RH side so I did not have to remove the muffler to get access. Hang the shaft to avoid stressing the outer CV joint.

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A pry bar and a spacer will pop the shaft out of the diff. Use care not to damage the dust shield.

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The 3.46:1 diff uses a 90 mm seal. p/n 33107505605 includes both the seal and the shaft retaining clip. The normal MT diff uses a different seal.

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A standard seal puller will pop the seal out easily. I had a good look at the seal before pulling it out and couldn't see any damage to the seal.

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Pulling the seal reveals the output shaft bearing. There is no need to disturb this.

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I used a seal driver set like this to install the new seal.

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The sealing surfaces on the output shaft looked good but there was a bit of suface corrosion on the shaft.

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I polished it up with crocus cloth to provide a perfect sealing surface.

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I decided to change the fluid as a precaution, despite the low mileage. I used a siphon tube to easily drain the diff.

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If you get the siphon tube geometry just right, it will completely drain the fluid. I made mine from steel fuel line.

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The drained fluid looked a bit murky. The internet is full of discussion about diff fluid turning dark. I attribute it to changes in the additive package under stress. Street driven cars may delay these changes but they seem to happen rapidly to track driven cars, regardless of the fluid being used. I am using Castrol Syntec 75W90 GL-5 at the moment but have seen it with Redline and others also.

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Torquing up the half-shaft bolts to 52 lb.ft. (per Bentley) I applied torque seal to the heads. This doesn't lock the bolts but provides a visual indication they haven't moved when doing a pre-track "nut and bolt" inspection.
Appreciate 0
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