Hey all, so I've had my 91 Z for something like 20 years now. I have replaced the rear hatch pull down motor and gear box assembly three times now. It clicked for me a couple nights ago when I did it most recently, I think a lot of failures and issues with these have to do with the adjustment of the whole assembly. Ypu can move the whole assembly dreely within three approximately 1/2" x 1/2" square holes in the bracket against the body of the car.

In the past I always adjusted it trying to get the right gap between the wing and the body on the outside edges, but I now think this was causing me to position it way too low. Listening to the pull down and release is a big part of this. Before, i would hear the motor rin, then slow down segnificantly as the hatch reached its lowest position, the motor slowi g is just indicating the load on it is increasing significantly. This puts way more force through the plastic gearbox housing, then leaves it untet significant tension as the car is driven. When releasing before, i would have to pull the release switch 3 or 4 times to get it to pop, reinforcing, the assemply was under way too much strain. I think all this causes many of the cracks and dailures people experience...

This time I used my old motor with my newer gear, seems the motor was the problem this time, more on that later...

I adjusted the whole assembly so that there was about a 1/16" of compression on the gasket / weather strip. If ypu squat down and look up above the license olate, ypu can watch it all the way down. I then used a small level to make sure the frame was perfectly vertical, i hace to think if it is on an angle, ypu will have way more drag, and it will over load certain slide bushings in the rails, which often crack... Now when it pulls down, I never hear any change in the pitch of the motor. (Except maybe for the last 1/4 of a second) There is no movement of the hatch , the gasket is just slightly compressed, and I expect the system to run much longer without service in this configuration!

Side note on the motor itself:
I started looking at this because the motor was starting to struggle and and I was smelling a faint electrical burning smell. I often had to help the hatch up and down. After swapping the old housing and motor, since last time I just stripped out the gear, I tore apart the motor. Turns out I believe the reason for my recent issues were that the worm was over greased, and a bunch of grease bypassed the little seal disc and had made it into the motor where the brushes make contact. I plan to clean that all up and see if it works again. Always good to have a spare!