Diagnosing Gearbox Problems

Diagnosing Electric Window Gearbox problems in your BMW CS

Window will go up and down but gets stuck 2 or 3 times.

If your window will go up an down but there seem to be dead spots along the way you are most likley having a problem with the gearbox. This problem may be preceeded by the window getting wedged in the upper or lower position requiring manual acutation of the motor via the access port in the door. When this occurs the metal worm gear will create a flat spot on the nylon gear.

Gearbox with nylon gear removed showing only worm gear

Nylon gear with flat spot caused by worm gear

The only solution is to replace the gearbox entierly or to drive out the nylon gear using a punch and replace it alone

Replacement Gearbox does not mount correctly

In theory the left and right gear boxes should be identical however there is some variation due to the mounting tabs having centering pegs on 2 of the 3 legs. I purchased a new gearbox at great expense only to find that it seemed to have the centering pegs on the wrong tabs.