I have a 1990 535i that shifts hard into fourth gear under light throttle but shifts much better under heavy throttle. The other three gears shift well. I have no codes and the fluid is red and properly filled. The driveshaft is new and the transmission mounts are too. Any thoughts about this?
It happened as the cruise control cancellation relied on the brake switch (which had failed). On a bad section under cruise I panicked (the first drive after buying it) and didn't know wtf to do. Braked hard against the engine and the tranny (and driveline) took a belting with the engine and brakes going head to head under WOT whilst i fought to exit the freeway where I wanted to- dumb move. I had hard shifts into 4th after that- no it was only the lock-up converter- ie. it would drop into 4th but when the torque converter locked up (shortly after this if driving under light load) the whole car would shudder. Shudder was only reduced if dropping foot off the throttle. Had two filter changes after that, changed to Castrol Synthetic (Transmax Z) (the only stuff ZF say is ok other than plain Dexrons). Over the next 40k the the problem has disappeared graduallly but completely. I suggest you get any werar material out of your filter as folows;
Do regular changes with Dexron in the short term and then switch to synthetic to make the tranny last for the long term.
in 5k- drop pan, flush filter (or replace) and replace fluid again using Dexron.
10k after that do a new filter, chg fluid to Transmax Z Synthetic (do not use anything else). 5 k after that do a new filter and more Transmax Z again- you only get 60% of the fluid as a whole load stays in the Torque Converter when you are dropping the transmission pan.
Get the bolt toques correct on the sump when you do it to stop any beding of the pan sealing surface, don't allow any dirt whatsoever into the sump and always clean your sump magnets well.
