5HP24 Operation & Torque Converter Design info

[civdiv99]

Every couple of weeks I get around to reading some of the posts here. Seems of late there's been discussion about transmission shuddering and similar issues.

A couple of months ago I uploaded a long post with discussion and pictures after I disassembled my 5HP24 and repaired (I won't go so far as to say what I did was a "rebuild") a problem. In my case, a bad bearing allowing axial play allowing fluid pressure issues allowing the "A" clutch to slip, etc. etc.

I've seen some discussion lately regarding the torque converters and possible shuddering caused by the lockup feature slipping/shuddering/whatever. Not attempting to solve anyone's specific issues here, but I did a lot of reading and scrounging around for docs giving theories of operation, power flow diagrams, and such before I began work. (For anyone that remembers my Nov post, the trans is still brilliant in operation).

On thing I found very interesting is that the converter in the 5HP24 is default status in the lockup position. Let me rephrase that - the transmission unlocks the converter with fluid pressure, not the other way around. I uploaded a couple of pages from a BMW transmission operation manual. I got an eye opener when I reinstalled my transmission after teardown and parts replacement. I had drained everything, so although I could fill the pan to the plug level, as most of us know then you start it up and finish the job, temperature specific, etc. When I first started the car, foot on the brake (it was not up on jack stands), it lurched a little, shuddered, and the engine died. I knew the converter was already in lockup from my reading, but I didn't really expect that. Started it up again, a little shudder, and then smooth as fluid pressurized and filled passages.

My point is this - the fluid used to unlock the converter and control it's gradual locking and unlocking during operation travels in passages in the 2 splined shafts (yes, 2 shafts, plus the tangs that drive the fluid pump) that engage inside the converter. My specific problem was a result of a bearing failure - but it was clear to me by all the sealing rings and so forth that I replaced on the various shafts that wear or other issues can certainly affect fluid pressures in a completely different physical location. So, for example, if the converter lockup is screwing up, but the computer and pressure solenoids are doing their job, replacing the converter may not necessarily be the answer. I have no idea if there's a way to test pressures in various parts of the system, but I will say there are a lot of blind plugs in the case which I suspect are there to be able to read pressures along various routes. The ZF rebuild manual I bought has a lot of scoop, but does not discuss this particular aspect. Nevertheless, for general info it's food for thought in deciding what may be going on with a particular trans operation.