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Transmission Oil Leak
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TOPIC: Transmission Oil Leak

Re: Transmission Oil Leak 4 months, 1 week ago #83329

  • cwbaader
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I don't think anyone on here believes it to be a trans input shaft leak. Experience has shown us that is the vent...PERIOD. Even though the top of the trans looks dry, its the vent...PERIOD. Fix the vent.

Re: Transmission Oil Leak 4 months, 1 week ago #83330

cwbaader wrote:
I don't think anyone on here believes it to be a trans input shaft leak. Experience has shown us that is the vent...PERIOD. Even though the top of the trans looks dry, its the vent...PERIOD. Fix the vent.


I hear you


If the vent is not a problem now, it will most probably be one later one.
So yes, I will make a solution for that before I try another shakedown of the car!


However, I think it could be two problems.
Both the vent hole (causing minor leak) and something leaking from inside the bellhousing (causing major leak).

How could so much oil get into the bellhousing, on the release bearing, and all along the input shaft and inside the tube (that covers the input shaft)?

How on earth could all oil travel from the vent hole down into the bellhousing - and at the same time leaving no tracks at all (just a completely dry surface)?

Doesn't anyone think that is strange?



So oil from vent hole is a common problem - that makes sense.

So how many of you got this huge amount of oil into the bellhousing when your vent hole was leaking oil?
Last Edit: 4 months, 1 week ago by bmwslangen.

Re: Transmission Oil Leak 4 months ago #83332

  • Ranger
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I don't have any input on the idea of fluid coming out of the vent making it's way into the bellhousing. I also would have thought "input shaft", but the guys in this thread that support the vent pipe theory are exceedingly experienced. Usually when I contradict someone that experience, I end up being wrong. And since I very much don't like to be wrong, I should keep my mouth shut.

Re. oil getting on to everything, once it gets into the bellhousing. No surprise. Once oil gets into the bellhousing, it would most certainly get on everything. The inside of a bellhousing would be a whirling hurricane, once the engine started turning.

If you decide to put a hose on the vent pipe, here's some info that might be useful.

If you put a hose on the vent pipe, the rules (I think) require you to put that hose in a catch tank. Chances are tho, the catch tank won't ever be used. When you route the hose up into the engine compartment, eventually you end up with a hose that climbs prob 2' higher then the vent pipe. That means that fluid would have to climb 2' up the hose in order to get to the catch tank that you've put in your engine bay somewhere. In my experience the fluid never climbs that high. I was certainly spewing fluid out my vent pipe so I needed the hose. But the fact that the hose climbs so high seemed to prevent any fluid from coming out of the hose.

The length of the vent pipe is pretty short. That makes it hard to put a hose clamp on. W/o a hose clamp, any hose you put on there will prob fall off. Only once was I able to put a hose and hose clamp on to the tranny vent, while the tranny was still in the car, and had the hose clamp stay in place. The other couple times I tried, the act of tightening the hose clamp popped it off of the vent pipe. I tried and tried, but it kicked my ass.

Ultimately I threaded in a hose barb. I don't remember the size of the thread, but it was prob 1/8NPT. I probably used a drill to widen the opening in the pipe a bit, and sucked up the fact that drilling the pipe would put a few metal shavings into the diff. Then I prob used some JBWeld on the threads of the hose barb.
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Last Edit: 4 months ago by Ranger.

Re: Transmission Oil Leak 4 months ago #83333

  • cwbaader
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To prevent shavings getting in the trans, pack the vent tube with wheel bearing grease. Clean after the tap drill and repack. Tap and clean...win!

Re: Transmission Oil Leak 3 months, 1 week ago #83376

Slow response frm me here, but been occupied with business trip to Ottawa and of course I catched a cold just when I came home. So basically nothing has happened in the garage...

The gearbox still lying there on the bench...

However, tomorrow is a track day which I don't want to miss! So now it's a race against the clock (and still not really recovered from that cold).



Good tips and tricks from everyone! Highly appreciated!

I agree - experience is invaluable! And I know how much experience there are here between all of you!

So I will not question experience at this stage, I will do the suggested changes and come back with a report



So this is my game plan:

1) I will do a quick check with the gearbox while on the bench
1a) Keep the gearbox slightly tilted forward (to simulate slight braking) and run the input shaft with a drill and see if something is leaking out from or around the input shaft.
1b) Keep the gearbox heavily tilted forward (to simulare heavy braking) and run the input shaft with a drill and see if something is leaking our from or around the input shaft.

2) Put back the gearbox in the car AND add a vent hose that is going up into the engine compartment.

3) Fill the gearbox with ordinary ATF but around 1 liter instead of the stipulated 1.3 liter.

4) Go out and drive on track day and see what happens!
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Re: Transmission Oil Leak 3 months, 1 week ago #83377

  • cwbaader
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DO NOT underfill the gearbox. BMW got it right and all you will do is exasperate wear on the box.

Re: Transmission Oil Leak 3 months, 1 week ago #83379

Ok, let's get straight to the point - you were right!

The problem must have been overflow from the vent hole!
But not due to expansion, foaming or wrong gearbox oil and so on.


I wanted to recreate the problem, so I had the gearbox on the bench,
filled to specified level and was running the input shaft with a drill.

With the gearbox completely level, nothing happened. Not a single drop.

But then I tilted the gearbox 45 degrees to simulate heavy breaking,
while the input shaft was spinning.

And now it basically was pouring out gearbox oil from the vent hole!





So the solution was to attach a hose (using an ordinary hose clamp) to the vent hole,
and it was then routed up as high as possible in the engine compartment,
with a small breather filter at the end.

When you had the gearbox tilted down it was quite easy to attach a hose,
and then secure it with a hose clamp (I tried and couldn't even pull it off).
But with the gearbox in it's installed position I declare it IMPOSSIBLE to get to that vent hole!



So I was wrenching like cray from 06.00 to 21.00 entire Friday to get the car ready for the track day the very next day.

Up at 05.30 on Saturday and away to Ljungbyhed (a former military airfield) - and success!

I could put in lap after lap without a single problem!





Thanks all for leading me into the correct path and actually thinking in other directions.
I still can't get over how bad I could misjudge the evidence in front of me.
But I should have known better - I know that oil in turbulent air flow can do basically anything!
Last Edit: 3 months, 1 week ago by bmwslangen.

Re: Transmission Oil Leak 3 months, 1 week ago #83380

  • cwbaader
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You're welcome. Never let it be said that anyone on this forum would say 'told you so:woohoo:

Re: Transmission Oil Leak 3 months ago #83383

  • Derrick
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bmwslangen wrote:
Ok, let's get straight to the point - you were right!


When you had the gearbox tilted down it was quite easy to attach a hose,
and then secure it with a hose clamp (I tried and couldn't even pull it off).
But with the gearbox in it's installed position I declare it IMPOSSIBLE to get to that vent hole!









I cut a hole in the transmission tunnel and I could very comfortably install the hose.

Re: Transmission Oil Leak 3 months ago #83386

Derrick wrote:

I cut a hole in the transmission tunnel and I could very comfortably install the hose.


That could be made into a nice access panel, that's actually a good idea!

I remember older cars sometimes had access panel to various places (I think the VW Beetle for example had an access panel to the shift linkage).
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