Odd auto-downshifting problem '90 300E

[Andy_M]

My 300E developed an odd issue with the trans a short while ago.

While driving down the highway on a trip of an hour or more, usually when you were on a downgrade, it would for no apparent reason, shift down into third. Once downshifted, it would not return to 4th no matter what you do until you pull over and stop - then once you continued on the trans shifted up through the gears normally and would not repeat the problem.

It did this very infrequently for a few weeks - always to my wife. Then it became more frequent, and was happening during even 1/2 hour trips. Same symptoms, same corrective action.

Last week it did it while I was in the car as well - only worse. This time it downshifted into 3rd on level road, stayed there for maybe a min, then either disengaged (like activating a trans brake) or shifted into neutral. We pulled over to the side, stopped, and started out again and it shifted up normally, but not into overdrive. We took the car home, let it cool completely, then drove it to a transmission shop owned by a friend of ours.

He pulled the trans, and found that the clutch packs are badly worn and breaking apart, that a rubber component that I can't recall the name of is worn out and breaking down, and are rebuilding the trans. This will only cost me parts and the trans did have 135k miles on it, so its fine, but the trans shifted fine before this started and I'm not sure I'm hearing that anyone actually identified the reason for the shift down problem. Perhaps the clutch pack breakdown was causing blockages that were reducing fluid pressure causing the issue? I would have suspected a crack in the valave body or something.

Has anyone else experienced this issue? What was the fix in your case? Any comments from any MB trans gurus out there?