Manual Transmission Leak
 

I noticed this morning wet spot on the garage floor under the rear end on my 1988 S4 5spd. I could see the fluid was clear and smelled like gear oil. It seemed to be coming from the transmission rather than the differential area. I did not see anything leaking from the output shafts behind the CV joints, and it did not seem to be coming from the input shaft. Is there a seal between the manual transmission and the differential? Are there some usual suspects I should check?

This leak seems to be brand new as of spirited drive on Sunday evening. Earlier in the day I was under the rear end trying to lower the suspension (improper sized wrench) and I didn't see any leaks and I gave it a good once over.


https://cimg0.ibsrv.net/gimg/rennlis...1a3b9aaa10.jpg https://cimg6.ibsrv.net/gimg/rennlis...7e33dd0380.jpg
These shots are from Sunday morning. Notice rear dif is clean and dry and no drips on the floor


https://cimg7.ibsrv.net/gimg/rennlis...2f47dcf6c8.jpg
Here the drip residue from the overnight. In the photo, I am now seeing a few other smaller spots. Which tells me I had a small leak that has gotten a little worse.

I did an archives search and didn't find any references to manual transmission leaks, are they fairly uncommon?

Mike
1988 928 S4 5SPD

Best way to find out where it is coming from is to jack it up and crawl completely underneath it. We had an '85 that leaked fluid out of the input shaft seal. Are you absolutely sure there is no leak in that area?

There is a seal for the differential cover too. See below. It is #11 on the diagram, part number 928 301 395 03. Check to make sure it isn't wet there also.

http://2eed5c4c51f4e23eb498-c3c64a2f...com/302-00.gif

Have you checked the brake fluid level?

No I haven't because I leaking fluid smells and feels like gear oil not brake fluid and it's dripping from off of the transmission, so I assumed it was gear oil.

I guess it could be brake fluid... Is there something about the brake system that would be leaking onto the transmission? I'll check the level over lunch, I have the car here at work today.

Could it be from the vent on the top of the case?

It would have to be super over filled

The puddle looked more like brake fluid and you mentioned that it was clear. There are hard lines that run above the tranny. And it's an easy check.

brake fluid will evaporate for the most part and not be goowie.
the smell is distinctive... no mistaking gear oil on the ground

those pics and the old spots look like it could be brake fluid depending on the time of those spots.

smell the oil on the ground.. that will be the determinant factor.

if it is.... top cover can leak but usually only when racing *(and really hot temps)

front shaft seal or real Diff seal.

Michael, can you tell us what was the cause of your leak?

The leaks was caused by a crack in the case. The crack was caused by an unknown protusion event from inside the case. The crack was patched with JB weld by one of the PO's and the patch failed. I fixed the crack with real weld.

Here is the post of the crack details:
https://rennlist.com/forums/928-foru...solutions.html

Here is the post of the repaired crack
https://rennlist.com/forums/928-foru...ase-fixed.html