'92 300SE - just replaced the passenger rear window regulator. Originally, I changed this part from the one that was there when I bought the car, thinking it was the problem behind my window failing to roll up properly.

As it turned out, that repair was not the problem, the motor itself was. Replaced that motor - all was well.

Yesterday, some how the cable in the mechanism skipped off the lower pulley. Try as I might, I couldn't get the cable back on, so I pulled the regulator and put the one that was there before back in.

Re-synchronized the motor after installing the regulator. However, when I use the express close method, the window goes all the way to the top and reverses like it's hit an obstruction.

I've pulled the power to the motor and re-synched 'till I'm blue in the face.

I've adjusted the upper stop to make sure the window closes properly.

I don't think I had this problem when this regulator was in the car originally - the express close worked fine - the motor itself would emit the dreaded pop-pop-pop noises at the top and bottom of travel.

How can the regulator be the cause of this problem - I would think it's motor related, but swapping the current motor for a known good one revealed the same results.

Any suggestions would be appreciated.

Regards