4l30e trans -- unknown cause of leak !!!

[swartze525i]

'92 525i

Had my 4L30E trans rebuilt a few months back. Master kit and new convertor. No work done on valve body, solenoids, etc. Few months later, extension housing and yoke ruined by obliterated bearing. New extension housing, bearing, seal, and yoke installed about 4 weeks ago.

Now the trans is leaking or blowing-off fluid from unknown area ONLY after driving for roughly an hour (highway). It's done this 3 times in the last 3 weeks, and have had to add fluid, drive, add fluid, drive, etc. to limp the car home. Have had to put trans in manual mode (3rd gear only) once or twice to avoid shifts, or lack thereof. Short jaunts around town do not produce this problem, even after trans warmed-up. No message center indicators such as "trans program".

Extension housing seal shows no signs of leakage, nor does the extension housing/trans housing mating point. No other visible signs of leakage such as accumulator, pans, etc. Correct fluid level on dipstick.

Any ideas?

[Bill R.]

Are you sure its the correct level on the dipstick and it was filled correctly at the right fluid temp? If its overfilled it will blow out the transmission vent tube on top of the trans at highway speeds.

[whiskychaser]

It does sound like atf is being blown out. Have you checked the cooler lines? If the atf is getting too hot it may foam. Not good for the tranny

[swartze525i]

Hi, Bill....I'm assuming when the trans was rebuilt, the mechanic filled it with the correct amount of fluid. (Of course, when one assumes....)

[swartze525i]

Whiskey....the mechanic said he back-flushed the cooler lines with whatever machine is used for this. Mechanic said it barely took any pressure to flush it and very little debris came out.....said that was a good sign that, internally, the cooler was clean and in good condition.

I've not seen foam on the dipstick when this recurring problem happens.

As far as the blow-off (if that's what is happening), when this occurs, it really drops my fluid level to the point of slipping or no shift at all (in automatic or "economy" mode), but will stay in whatever gear I choose in manual or "sport" mode). Are these common and to be expected?

I would think that it would only blow-off excess fluid....but then again fluid expands when the temp rises, correct?

Could there be a problem with the venting.....or something else internally that is causing excessive pressure to build up?

[whiskychaser]

If you dont have enough ATF you wont get the pressure to shift normally. In S mode, the pump works harder and achieves it. If you select a gear manually, you wont be using that line pressure.
The main thing is to find out if it is really coming out of the vent. Incidentally, I see you also have a '92? Is it pre 9/92 with the cooler in the rad? If so, is the ATF colour (what's left) normal?