Here is an email we recently received. This is becoming an increasing problem as these cars age. Per my instruction manuals, if the sunroof motor and gearbox (transmission) are working, you can "power out" the cable with the switch once the forward end of the cable is disconnected. Try the following based on what your symptoms are.
Problem & Solution
Common among these chassis:
1. If the motor is not running, unplug it back in the trunk and power it directly with a 12-volt power source ( battery, booster, power probe, etc)
2. If the motor is running but the cable is not coming out, try pulling hard on the cable end while running the motor at the same time.
If neither of the above help, you either have a bad motor ( no. 1 above ) or a stripped gear or cable inside the gearbox ( no. 2 above ). Now you have some serious and sometimes "painful" work to do. You will have to take the clutch bolt out of and the cover off the gearbox with the assembly still bolted up inside the trunk. I do not have a video of this procedure. You may be able to google the subject for additional guidance. I will try to explain here and add some pictures as time allows. If you have any good pictures of this procedure please email them to us so we can share with other owners.
It will be hard to see what you are doing. A good light and a mirror may help, but in the end, you will have to work by "feel." The bolts holding the cover plate on the square gearbox are 8 mm. This cover plate needs to be removed first. On some models, you can gain more access by unbolting the motor bracket from the car's body. You won't be able to take it out but it will allow you to tip it for better access to the cover bolts.
In the picture about you can see the cover plate held on by three 8mm head bolts. This is from a mid-1970's Mercedes. The design of the motor and mounting method may vary but they all have a cover plate. This plate must be removed.
In this picture, you are looking at the assembly out of an early 1980's Mercedes. After you remove the place you will need to remove the big nut on the clutch / gear drive shaft. Keep track of how it all comes apart so you can put it back together properly. The assembly below is from a late 1980's model with a tilting sunroof. Note it still has a cover plate ( 3 bolts only ) and a center drive bolt.
Once you remove the cover plate and the big nut you can push the gear out of the transmission. You may have to "fight" to get this all out. Once you get the drive gear out you can pull the sunroof cable out by hand.
You have to fix the motor or the gearbox and cable before reinstalling. Make sure the motor is running and to reinstall the cable you can "power" it back into the transmission using the sunroof switch.