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e9Leveque

e9Leveque

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Engine runs, very minor oil leak I had to deal with, but I have a very obvious transmission leak. Grrrr. I suspect I’ll need to drop transmission and make sure I have all of the seals installed correctly. One thing I came across was post#2 in this thread
https://e9coupe.com/forum/threads/transmission-removal.8351/
which says “make sure to put liquid gasket between bellhousing snd transmission”, which others then agree with, but I’m with the original poster - shouldn’t the transmission be a sealed unit while the bell housing remains dry? I do seem to have some leak there, which would seem to indicate a leak from the front of the transmission. I suppose if I had placed a liquid gasket sealant I wouldn’t see that leak but isn’t that then just hiding a leak which is slowly building up within the bellhousing?
These same questions were asked in the prior thread but no answer…
 
The trans itself should be sealed. The bell housing just bolts to it. There is nothing to seal between the trans and the bell housing, and the bell housing is more or less open to the outside world.

Sounds like a front trans seal...
 
My thought as well, on both counts (front seal and open to air). So why then the recommendation for sealing that interface?
 
I forgot which transmission you have?
I think there were 2 different 4 speeds in our cars over the years. The getrag does not need sealant there, the trans case is sealed. But there is a cover for the input shaft that needs a gasket or sealant.
 
New 5-speed, the 265/5 non-dogleg. The transmission came to me “sealed” but I suspect one of the seals that I needed to put on may not be on there fully. At least when I take it apart it will be obvious because there will be a drip line!
 
Just another thought, are you sure it's oil and not brake fluid? If the slave cylinder is leaking it would/could drain of the bottom of the bell housing. It's a lot easier than pulling the trans out. Another thing, did you put lockite on the flywheel bolts? I've seen oil leak thru those bolts before too. Good luck.
 
I don’t believe it’s brake fluid since the reservoir hasn’t drained much. I did rebleed the slave cylinder since the clutch felt a bit loose but there didn’t seem to be any issue there. But good point - I’ll collect some of it and see. It also significantly picks up speed in draining when the engine is running which I wouldn’t imagine brake fluid would do. It also doesn’t feel like the same consistency as the brake fluid.
I guess three possibilities - transmission fluid, brake fluid or oil. I’ll collect a bit and assess before I drop the transmission, but I’m already getting in the mindset of having to do that…
 
Hmm. Can you explain that? I thought oil pressure light was from sensor off the side of the head - I added a pressure sender there. I assume you’re talking about something else…this leak is way down low.
 
If it is leaking from the oil switch it will run down the back of the engine and drain off the bell housing. Easy to check, just take a look the switch, if you see oil there that's your problem.
 
I had to cheat (I consider using AI cheating)...

"The infamous "duck" gasket refers to the small, distinctively shaped rubber seal on the rear timing chain/cam cover of BMW M30 engines (found in classic CS/CSi models like the E9 3.0CSi and E24 635CSi). It frequently causes elusive, frustrating oil leaks at the back of the cylinder block."


Screenshot 2026-05-31 at 7.54.03 AM.png
 
Hopefully you find that the oil leak is a simple fix and dropping the transmission is not needed. If you do end up dropping it, you may find this seal kit helpful. I used it to re-seal my transmission before installing.

www.bimmerworld.com

Transmission Seal Kit for Getrag 260/262/265 Manual Transmission

Set of OEM oil seals to prevent or eliminate leaks from your Getrag manual gearbox.
www.bimmerworld.com www.bimmerworld.com
 
Perfect, that is helpful. I know that the engine itself did not leak previous to my removal of the old transmission and the engine from the engine bay. I did change out the oil pressure sender, so it is very possible that that is the source of the leak, but otherwise it has to be something within the engine to Bell housing to Transmission interface since those are the parts that I had changed. I suppose it is also possible that the transmission that I bought has an internal leak, but the seller told me that they had filled it and did not observe any leaks. It was from another member here and I have no reason to doubt him. Unfortunately can’t deal with it today, have my daughter’s high school graduation party, but I know what the next week of evenings is going to entail.

I’ll also say that I thought Don was pulling my leg with that “duck” gasket, since I hadn’t come across that term before, so I’m glad for the explanation :)
 
Congratulations on your daughter's graduation, and condolences to your bank account, now that presumably she is off to college!! Man, glad that is behind me! My older son attended NYU..YIKES!! Fortunately his mom worked at Stanford, so we got a 50% discount. STILL hella expensive! Just finished paying for that a couple of years ago..15 years after he graduated!

Sounds likely that this is a trans seal leak. Holding oil when static is one thing. Holding oil when turning is another. From what I gather, other than the joyful experience of pulling the trans, changing the front seal is pretty straightforward.

Your experience has taught me to change the seals on my old Getrag 265 before I put it in the car.

Where did you source your modified driveline for the 256 conversion?
 
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