DIY: Fix the DCT Fluid Weeping Problem (Mechatronics Harness O-Ring)

[Theodore]

Warning: This DIY requires very long arms, I found it barely reachable with a 6 foot arm span.

A tiny, overpriced O-ring (BMW Part# 28607849555) at the top of the DCT slowly fails:





DCT fluid seeps past the failing O-ring on the top of the transmission where the DCT wiring harness plugs into the DCT mechatronics unit:



Which then pools in the crevices of the DCT structure, but it eventually drips down the side of the DCT transmission:



And creates a weeping effect:



On eBay, it seems nearly every E9X M3 DCT transmission that has not been cleaned up prior to photographing shows signs of fluid leaking past this mechatronics harness O-ring.





Unlike other BMW Getrag DCT transmissions, we don't have to change out the entire Mechatronics sleeve (as seen in some videos online for other BMW's with DCT transmissions) in the E9X M3 DCT as it has a replaceable o-ring on the Mechatronics sleeve (BMW Part # 28607849555).

1. You need to raise all 4 corners of the car for this repair.

2. Remove the exhaust on your car. First remove the rear section of the exhaust (see the Axle-Back DIY Exhaust Removal from shiblanor)


and remove the mid-section of the exhaust as well (see the Fabspeed X-Pipe DIY Install from jo8M3)


3. Remove the heat shields covering the DCT and the driveshaft.

4. Support the bottom of the DCT with a jack and remove the DCT support bracket.



5. Disconnect the driveshaft from the rear of the DCT transmission and support the driveshaft out of the way, but in a manner that keeps it relatively parallel to the differential.

6. Using the jack under the DCT, slowly lower/tilt the rear section of the DCT downwards.



7. Using very long arms reach in and disconnect the DCT wiring harness from the mechatronics sleeve. This is done using a counter-clockwise turning motion of about 1/4 of a turn on the outer plastic wiring harness where it connects to the mechatronics sleeve.



8. Insert the temporary protective cover over the exposed mechatronics sleeve electrical prongs (BMW part # 83300494213).





9. Thoroughly clean the exposed portion of the mechatronics' sleeve and the surrounding area. I used brake cleaner sprayed onto a rag to avoid over-spray onto the wiring or possibly into the DCT.

10. Remove the machine screw (T27) holding the mechatronics sleeve in place.



11. Pull the mechatronics sleeve out of the DCT by approximately 2 inches exposing the mechatronics harness O-ring.



12. Very carefully, using a pick or similar tool, remove the mechatronics harness O-ring by sliding it over the mechatronics sleeve towards you (towards the rear of the car). The O-ring is flexible enough to go up and over the "arm" that the T27 bolt sits in.



13. Place the replacement mechatronics harness O-ring on to the mechatronics sleeve back into the same location being careful to position the tallest end of the O-ring on outwards (towards the rear of the car). The new O-ring will stretch up and over the "arm" that the T27 bolt sits in without deforming.



14. Reassemble everything in reverse order.

Sources for this DIY

Borrowed images and ideas from this page.

BMW TIS which states you must fully remove the DCT from the vehicle to complete this job.

[M43S7RO]

How did you look up there to confirm it was that and not the mech cover weaping?

[Theodore]

I noticed it when I removed the driveshaft for other work. Even without lowering the transmission, if you have the heat shields off you can use your phone in conjunction with a work light to see the fluid pooled up or you may be able to reach your hand up there and feel the fluid sitting on top of the DCT. My suspicion is this leak is commonly misdiagnosed as a failing mechatronics side cover gasket or DCT pan/pan gasket.

[Locksmythe]

Impressive work here!

[BayE30]

To bad there isnt an upgraded O-ring to replace the failure prone rubber one...

[For3]

Thanks a lot! Great work OP. I am assuming the answer is yes, but I take it the O Ring is flexible enough to go up and over the "arm" that the T27 bolts through?

Also the TIS warns of potential damage if the area is not cleaned thoroughly. After you put the protector sleeve in, what did you use / do to clean the area?

[da jemster]

Thx for this OP!

$30 for an O-ring?!?

Admins - can we sticky this?

[da jemster]

How come the o-ring is on one side, in pic #11, but on the other side in pic #13?

[BayE30]

Originally Posted by da jemster

How come the o-ring is on one side, in pic #11, but on the other side in pic #13?

cuz its mid-install, and highlighting make sure the orientation is correct before installing all the way.

[Theodore]

Originally Posted by For3

Thanks a lot! Great work OP. I am assuming the answer is yes, but I take it the O Ring is flexible enough to go up and over the "arm" that the T27 bolts through?

Also the TIS warns of potential damage if the area is not cleaned thoroughly. After you put the protector sleeve in, what did you use / do to clean the area?

Yes, it stretches over the bolt arm with a little finesse, but not so much that it damages the O-ring. I used brake cleaner sprayed onto a rag to avoid over-spray onto the wiring or possibly into the DCT. Added both notations to the original post, thanks.

[jun_e92]

The E9X M3 DCT can be lowered a bit. Can I replace the mechatronic side cover Gasket?

[Audioslave686]

Originally Posted by jun_e92

The E9X M3 DCT can be lowered a bit. Can I replace the mechatronic side cover Gasket?

that's doubtful.
I just finished that DIY (it was not fun at all)
you can only lower the transmission for about 2 inches.
that's definitely not enough to get to the whole side cover

[gnjax]

Originally Posted by Audioslave686

that's doubtful.
I just finished that DIY (it was not fun at all)
you can only lower the transmission for about 2 inches.
that's definitely not enough to get to the whole side cover

were you able to confirm there was a leak there for you as well ?

[Audioslave686]

Originally Posted by gnjax

were you able to confirm there was a leak there for you as well ?

It's only started to weep in my case.
I was replacing DCT cooling hoses so I decided to replace that o-ring as well

[kyippee]

I'm not very good as a mechanic so excuse my question.. but does this require transmission fluid to be replaced?

I'm having a shop to transmission, diff, and rear subframe mounts along with the driveshaft guibo and lots of bushings. Thinking this will be something we can do while we're in there.

I already have the Slon DCT side and bottom pans, and noticed a bit of weeping of fluid. Maybe this is it!

[Theodore]

Originally Posted by kyippee

I'm not very good as a mechanic so excuse my question.. but does this require transmission fluid to be replaced?

Not required.

[da jemster]

Theodore , I just finished doing my RBs and I still have the subframe off and the engine supported on the lift bar. Do you think I will have more clearance on the passenger side when reaching up for the mechatronics sleeve?

[Theodore]

Originally Posted by da jemster

Theodore , I just finished doing my RBs and I still have the subframe off and the engine supported on the lift bar. Do you think I will have more clearance on the passenger side when reaching up for the mechatronics sleeve?

Unfortunately no, the space between the transmission tunnel and DCT (when bolted into position) is too tight a space to work in, with or without the front suspension subframe in place.

[da jemster]

Originally Posted by Theodore

Unfortunately no, the space between the transmission tunnel and DCT (when bolted into position) is too tight a space to work in, with or without the front suspension subframe in place.

Thank you Sir!

[da jemster]

When you pulled back the driveshaft, which bolts did you remove - the ones for the driveshaft or the ones for the guibo? Also, after loosening the lock collar on the driveshaft, did you have to lower the support for the Center Support Bearing? If you did, don't we have to "pre-load" it when re-installing?

[Theodore]

Originally Posted by da jemster

When you pulled back the driveshaft, which bolts did you remove - the ones for the driveshaft or the ones for the guibo? Also, after loosening the lock collar on the driveshaft, did you have to lower the support for the Center Support Bearing? If you did, don't we have to "pre-load" it when re-installing?

Removing the giubo from the transmission output shaft gives you more room to work. The driveshaft probably won't disconnect from the transmission without the center mount bearing being unbolted and if you mark the position of the flanges before removal, you can apply the same factory pre-loaded tension when reinstalling. BMW does not specify a pre-loaded tension amount for the driveshaft in the TIS.

[da jemster]

Originally Posted by Theodore

Removing the giubo from the transmission output shaft gives you more room to work. The driveshaft probably won't disconnect from the transmission without the center mount bearing being unbolted and if you mark the position of the flanges before removal, you can apply the same factory pre-loaded tension when reinstalling. BMW does not specify a pre-loaded tension amount for the driveshaft in the TIS.

Thx again Theodore ! I was able to move the driveshaft out of the way, without uninstalling the guibo, when I dismounted the CSB carrier. And yes, I marked the position of the 2 screws before dismounting :-)

And...I learned a hard lesson - NEVER, NEVER lower the tranny when you don't have the engine on its mounts and only having it hanging by the single lift hole by the passenger side. As I lowered the DCT and as I was inspecting the Mechatronics, I didn't realize it swung so far out and was pressed against the passenger side of the tunnel. I lifted the tranny back up but it was so cock-eyed leaning to the passenger side. So I decided I need to put back the subframe, hoping it would straighten it out. Unfortunately, I couldn't line up the subframe to the chassis because it was off as much as 6 inches! It took me a couple of hours, a Harbor Freight engine jack holding the tranny, 3 different jacks to line eveything up again...all on my back.