ZFHP22 transmission failures in E34's?

[pundit]

I'm interested in finding out more about the gremlins that plagued the ZFHP22 auto transmissions. I know these things could burn out the front clutches while being held at revs in "Park" or "Neutral" but my understanding that occurred prior to about 1987. From the time the E34 535iA came out with ZFHP22's fitted this problem was apparently rectified. Yes? No? Anyway here's some info I found while researching the problem...

"...The ZF automatic is engineered to run some ridiculously high line pressure in Park, Reverse, and Neutral, (P.R. & N.) around 190 psi., (anything over 70 is a waste in P. & N.). The input shaft has a hole in it that feeds the forward clutch. This hole is sealed (isolated, if you will) off by a rotating metal sealing ring on either side of it. The rings seat inside the stator shaft of the pump. The stator shaft splines into the torque converter.

A little ring, bore, and bushing wear; I mean just a tiny bit, and you have torque converter pressure (190psi in P, R, & N) leaking past the front ring, into the forward clutch circuit. The clutches then drag (you usually can't feel it) and burn up very quickly. Limiting operation in Park, Reverse, and Neutral to an absolute minimum will extend the transmission life considerably.

When I rebuild a ZF, I use some "tricky" re engineering. First, I provide a "line to lube" pathway, increasing lube oil available to the gear train under high throttle conditions. Second, I machine a pocket in the valve body casting to accept a .250" check ball. Then I fabricate a hole and seat for it in the separator plate in the forward clutch exhaust circuit bypassing the insufficient orifice type forward clutch exhaust system. Third, I shim the accumulator springs to firm the shifts somewhat without raising line pressure past dangerous limits like cheap shift kits do, which aggravates the ring leak conditions in the forward circuit as well as all other circuits.

This tech is available in the Trans industry, but is seldom used, as the time necessary to create one of these units is considerable. I am lucky enough to be sort of semi-retired and can take whatever time I need..."

I didn't post the author's name as the post is a few years old. Anyway can anybody shed some light on these transmissions? I know most will simply say "Get a manual!" but I commute in traffic and frankly I'm over it after driving manuals for 25 years!! - Cheers

[George M]

the issue is still endemic to the E-34 and E-32 but less prevalent as some internal changes were made after the early era of the E-23. Still not a good idea to rev aging E-32/34's with that trans in neutral or park "after" initializing trans pressure by driving the car. If you ever go for emission testing which requires that practice....let the car shut down for a full half an hour to let internal trans pressure subside before starting the engine back up and then don't put it in gear until after the test. The ZF 4 HP 22 EH takes a lot of criticism for this much publicized issue. Point of fact is that particular trans out of the entire family of BMW auto box's is my favorite. Mine has 150k miles on it and has never been opened up except for on schedule filter changes and still shifts wonderfully. I just rarely rev my engine for sustained periods after driving the car in park or neutral and can live with that. Don't mind giving it a blast once in a while in park or neutral though...to hear the song of the big six.
HTH,
George

[winfred]

if you are worried about revving it while working on it, put it in neutral and get the back tires off of the ground so they can spin, this takes the pressure off of the clutches. i replace the steel rings with teflon rings and have been doing them for about 5 years now with success