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      02-23-2018, 05:55 AM   #1
Theodore
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DIY: Fix Your Leaking Differential

Is your E9X M3 leaking oil from the rear differential? Most likely it is due to a failing axle or pinion seal. Here's how you fix it:

Assess What is Leaking:

1. At minimum you need to raise the rear of the car, lifting all 4 corners is best for this repair.

2. Identify where your differential is leaking and how many seals you need to replace.

Leaking axle seal:


Leaking pinion seal:

Image borrowed from testdriver here.

For Axle Seal Repair:

Specialized tools you'll need:

- E14 Torx socket (swivel version - better, impact swivel - best if you have an impact ratchet)
- Something to remove the seal from the differential "ear" flange (seal driving kit - acceptable, piece of pipe slightly smaller in diameter than the seal - better, BMW specialty tools - best)
- Something to re-install the seal into the differential "ear" flange (seal driving kit - acceptable, this particular oil filter - better, BMW specialty tools - best)
- Something to remove and replace the retaining ring and the rubber o-ring seal (metal picks - better, BMW specialty tools - best).

E9X M3 axle seals, BMW Part # 33107510289 (one for right side and one for the left side, identical, consider purchasing one extra than you need in case you damage one during install)

Image borrowed from here.

E9X M3 differential o-rings, BMW Part # 33111214144 (one for right side and one for the left side, identical)

Image borrowed from here.

A. Remove the rear section of the exhaust for axle seal only repairs (see the Axle-Back DIY Exhaust Removal from shiblanor).



B. Hang your axles supported by something such as zip ties.



C. Unbolt your axle(s) using a Torx E14 socket.



D. Mark your axle flange and pop it off with 1 or 2 screwdrivers:





E. You can easily remove the old seal by hammering the seal out with a piece of pipe the same size or carefully pull it out with a pair of pliers or seal removal tool.

F. Use this oil filter socket (or something else of the same size) to drive in the new seal until it covers only half of the oil relief hole. Lubricate the sides of the axle seal with diff fluid. Use a metal pick to remove and replace the rubber ring seal around the outside of the ear.



G. Pull the small retaining ring out of the differential and replace it with the new one that came in your axle seal kit by pre-installing it in the differential.

H. Reinstall the axle ear (tighten bolts to 19NM), push in the output drive flange (with new retaining ring pre-installed inside the diff) and then re-attach the axle (tighten axle bolts to 120 NM).

Great video from Lars Fuglsang that explains some of these concepts:


For Pinion Seal Repair:

Specialized tools you'll need:

- E12 Torx socket (swivel version - better, impact swivel - best if you have an impact ratchet)
- Something to remove the pinion seal from the differential (seal puller tool - better, BMW specialty tools - best).
- Something to drive the new pinion seal back into the differential (Miller Pinion Seal Installer 8891 - better, BMW specialty tools - best)

E9x M3 pinion seal, BMW Part # 33121213949 (one total, consider purchasing one extra in case you damage the first one during install).

Image borrowed from here.

E9X M3 pinion nut flange, BMW Part # 33121205138 (one total)

a. Remove the mid-section of the exhaust as well if you need to replace the pinion seal (see the Fabspeed X-Pipe DIY Install from jo8M3)



b. Remove the heat shield closest to the differential.

c. Remove the 6 drive shaft bolts. A torx E12 socket will be needed. Mark the position of any colored (weighted) bolts to return them to the same position. If you are following BMW's recommendation to replace all of these bolts, be prepared (or prepare in advance) to have any needed specialty (green or black) bolts on hand.



d. Mark the position of the pinion nut with a line, remove the flimsy pinion nut retainer and count how many thread rotations is it to the return the pinion nut to its original position (not shown). Also draw the same line on your socket (32mm).



e. Use puller (this cheap one works fine for this job) to remove driveshaft flange.



f. Remove the leaking pinion seal with a seal puller tool.





g. Use a seal driving tool to hammer in the new pinion seal flush with the lip oft the differential (the Miller Pinion Seal Installer 8891 is widely available on Ebay, sells for cheap and offers great fitment for the E9X M3 diff). Coat the sides of the seal with diff oil.



h. Admire the new pinon seal, coat the face of the drive flange with oil and reinstall everything in reverse order. Top off the differential with oil (you'll lose just a little during this fix). The online TIS offers up two competing torque specs for driveshaft to differential bolts (ZNS M10 with ribs), which to appear to both offer a final torque value very similar to one another, either:

20 NM + 90 degrees additional turn
or
40 NM + 45 degrees additional turn

__________________
E9X M3 Common Torque Specs Can Be Found Here
E9X M3 Exact OEM Equivalent Parts Can Be Found Here
What I Wish I Knew When I First Bought My E9X M3 Can Be Found Here

Last edited by Theodore; 02-24-2018 at 04:55 AM.
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      02-23-2018, 08:07 AM   #2
SYT_Shadow
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Very nice! Thank you for the DIY!
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Theodore259.50
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      02-23-2018, 08:42 AM   #3
pbonsalb
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I agree. Great job. Thanks from a fellow DIYer who has not yet had to do this job but probably will eventually.
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