A loud crack opening the roof on a 964 Cabrio?

These cabrio locking roof motors are starting to have common issues of the gear motor breaking.

This vehicle has now experienced this twice. Once with each motor.

These locking motors contain 2 worm gears and a bevel gear. It is most common that the bevel gear breaks a tooth....or more.

There is a microswitch inside which is activated by a small plastic piece, sat on the bevel gear, at either end of the travel. This turns off the power to the motor. In theory this works well, however the plastic parts needs to be very accurately placed so that the motor is turned off early enough in either direction so as not to put pressure on the gear and break teeth. These gears are made from quite soft brass.

These motors were dissasembled. Cleaned and reassembled with new grease with care taken to adjusten the activation of the microswitch. However the likelyhood is that with use and time these will again break. I have some parts in mind that would possibly improve the design. If next time the gears break I will make them and try them out.

These roof motors, by virtue of age - will have all its grease dried up inside, leading to increased friction and/or sticking and jamming. The weight of the roof + mechanical leverage via the mechanism is being held on a single contact point during operation of the roof, which at some point yields and breaks. The owner of this car experienced exactly that.