ZF4HP22 occasional harsh shifts.

[pundit]

Sometimes my ZF4HP22 changes fairly harshly but then it will shift just fine again. I also sometimes get harsh downshifts just prior to pulling up. It seems like the trans is sticking in gear then suddenly releases with a thump as I pull up. Any suggestions?

I have experienced harsh changes on a variety of auto transmissions (non ZF) when cold. This is often due to hardened piston 'O' rings in the valve body which tend to stick when cold and cause late changes which are often fairly harsh when they final occur at higher revs than normal. Once everything warms up and the seals become softer the shifts tend to settle back down again. However my ZF problem doesn't appear to be temperature related as such, and therefore I'm suspecting something else - sticky electric solenoids maybe? I just performed a trans service last week. New gasket, filter & Dexron III. Everything looked fine. The original fluid wasn't too discolored and there were minimal metallics on the pan magnets. Apart from the random harsh shifts there are no other unusual symptoms. (No creeping in neutral)

Cheers.

Stock 1990 535iA 170,000kms

[Dan in NZ]

I would have suggested changing the fluid, but since you've already done that... How about unplugging the transmission control module for a few minutes, then plugging it back in, to reset it. Have you checked the fluid level again?

The zf in these bimmers is programmed to shift a bit harder when it's cold, perfectly normal.