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Tech Article

BMW E30 3-Series Leaking ZF 4HP-22 Automatic Transmission

Last Updated: 03/23/2017
Parts Group: Transmission
This article discusses the automatic transmission (specifically the ZF 4HP-22) as used on the E30 with the main focus being on me trying to locate the cause of a leak. If you're not here for the technical analysis but would rather buy a used unit from us, guaranteed to work and fit ... then please select the link below.The information herein is based on my own 1989 BMW 325i. It was cheerfully dripping red transmission fluid when parked, and it needed a transmission service anyway, so I asked my tech to drain the fluid, drop the transmission pan, replace the filter, replace the gasket, and then put it all together again and fill with fresh fluid. Much of the agenda involved chasing the leak. My hope was that the oil pan might be leaking. Not so, as was shown by the leak continuing even after the service, and by the location of that leak: it was dripping from the little plastic stone-guard grid that covers the hole at the bottom front of the transmission.

I have several of these transmissions around my shop, so my tech and I peek inside the relevant area of one of these.

Much of it is solid metal, or solid bolts-in-bolt-holes, and the fluid can't leak through that. The most likely two places were the center section, which I understand to be the oil pump, and the two shafts (one inside the other) that fit inside the torque converter. If fluid is leaking out of the torque converter, that would explain it.
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