The Official 356Talk Forum

How fast should the sunroof motor turn when it's not connected to the sunroof?

The motor in my 64 was working fine until one day it stopped and would just blow the fuse if you tried to run it. I removed the motor(PITA) and it was fried inside so I sent it out to be repaired. It needed the armature and the field windings redone. I finally got it back and reinstalled it in my car(even bigger PITA). I tested it before I hooked up the drive cable and it spins extremely fast with no load. But I never ran it before without a load so I don't know how fast it should turn under those conditions.
I double checked the sunroof drive and I can spin the drive cable by hand to move the sunroof back and forth with mild resistance. I hooked the drive cable up to the motor and turned on the switch - promptly blowing the fuse. So I pulled the cover off of the drive mechanism and lifted out the drive wheel so I could slide the cables back and forth. They moved OK, but I added some fresh grease and slid them back and forth until they moved pretty easily. Then I realigned the drive posts and put the drive wheel back in. Turned on the switch and promptly blew the fuse. I am running the correct 25A fuse. During these tests I didn't have the roof panel connected to the cables so there was no real load.

I don't have a readily available way to test the speed of the motor, but think starter motor speed with no load. Maybe thats just the way they are supposed to be, but I'm wondering if its possible that they rewired it wrong? Anyone have a sunroof motor they can test and see if it spins really fast with no load?

And if that isn't the problem - any suggestions?

Larry: Connect a battery powered drill to the drive cable to confirm the top will move open and closed with no binding.

bob lerche wrote:Larry: Connect a battery powered drill to the drive cable to confirm the top will move open and closed with no binding.

Good idea Bob. I just tried it and my cheap, HF cordless drill had no problem running it back and forth. It didn't have much of a charge so I ran it back and forth a few times and when it was obviously running low of a charge I ran it back to the forward position. After it's recharged I plan to cycle it a few more times and then connect the roof panel and see how it does.

I don't know how many amps the little 18V HF drill is, but the actual motor size is smaller than the sunroof motor. I'm going to pick the brain of the electrical engineer who lives across the street when I see him. But I'm starting to suspect the rebuild of my motor.

The motor will spin way faster then one would expect under no-load conditions. BUT...Caution! The type of motor is such that operating under no-load conditions will cause it to reach an early demise. In addition Larry, it sounds like maybe your motor was improperly repaired. Very brief testing like less that a second prior to installation is ok.

Solved!
I decided to pull the motor back out and pop the covers and take a look inside. Glad I did. Eurton Electric, who usually does good work, had a bad day. When they soldered in the new field windings their employee made a pretty big pile of solder (pix below) that was so high it contacted the aluminum cover when he popped it on. Electricity takes the path of least resistance so obviously it was easier to spin the motor with no load. As soon as the motor had a load by trying to drive the sunroof panel is would take the easier path through the aluminum cover causing a dead short and blowing the fuse. I re- soldered the connection correctly and now the motor has no problem moving the sunroof panel back and forth.