Hi,
today was the day that my driver side window got stuck at full-open. The alarm sounds as soon as I approach the car, so repair was inevitable. It does not rain yet... but it will tomorrow ;-)

I opened the door, took off the covers, and had a look again at the windows mechanism. You just can't get it up again without un-screwing the motor, so that is what I did. Took the motor with the gearbox off, and found out that it was not running at all. 12V was on when engaging the switch. So far so good. Especially when you think for a moment that in my drivers door, all the wires that go to the window-motor have been worked on to locate broken wires. Seems PO's had trouble before ;-)
 
First I thought it would be the overload sensor inside the motor again, but this time it was ok. I took the motor apart, and saw the culprit. Water has entered the motor, and oxidized quite a bit. One of the brushes was stuck, causing the motor to stop randomly, and work again if you hit the door (open/close/.....).

Theo

1988 928s4 cherry red

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Will,
actually.. (just trying to be well informed, humble, thoughtful, so probably never getting very rich, and doing most of the 928 myself ;-))

Taking out the axle of the motor is something you need to do with great care. First you unscrew the torx screws that hold the motor to the gearbox. Then gently take gearbox loose from the axle. The axle has a worm wheel as you can see in the pic, so you may need to turn it a bit to unlock it. The plastic is a bit frozen, and needs a bit of wiggling. It does come out. I used a bit of WD40 to get it moving. You must <not> pull hard on the rotor, since it will damage the brushes.
When you have taken everything out, a good deal of cleaning is required. Sometimes water has corroded everything. Also make sure the brushes move easily, and are not worn too much. You can see the black gizmo next to the brushes, which is the overload-protection of the motor. They do fail sometimes leaving the circuit open, and the motor inoperable.
When re-assembling, it is a good idea to apply some grease at the rear bearing, and at the area where the worm enters the gearbox. Also have a good look at the electrical connectors since they do corrode.

You might use this opportunity to look at the window guides and solve any problems with play or wear.

Good luck,

Theo

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S4-GT-GTS Motor assembly left (10 teeth)        S4-GT-GTS Motor assembly right (10 teeth)

Hi, you made me check again, but in fact there are two part series involved when talking power window motor and transmission assembly.
 

Funny, the numbers seem un logical in sequence but this is just the way it is. It is also why the new style unit opens the window faster that the old style.... about 25%

Really, it is a but confusing but Porsche lists the assembly in total and specifies the motor and transmission separately, but also has combined items in PET. I have swapped the motor itself from one model to the other and that seemed to fit and work without problems.

Theo
1992 928gts Midnight Blue
The Netherlands
http://jenniskens.livedsl.nl
http://928gts.jenniskens.eu

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Did you know that SAAB makes an identical motor?

Porsche 928 window motor 85 to 95 is exactly the same as the motors used in the following SAAB models


SAAB 900 2.0 L 8v 79 to 88
16v 86 to 90
2.1L 16v 91 to 94
2.0L Turbo 8 v 79 to 84
2.0L Turbo 16v 85 to 94
SAAB 900 86-93 window regulator 8567646 or 8567638 or 8722209
(Careful, the SAAB 900 II is different, compare!!)

It uses a plastic cover that completely covers the motor and prevents water landing on the motor. If I recall I had to break a small piece off to fit the Porsche 928 set up. I found it impossible to stop water coming in via the window seals!!

These motors/ covers are much cheaper on SAAB ebay site!!!

Theo
1992 928gts Midnight Blue
The Netherlands
http://jenniskens.livedsl.nl
http://928gts.jenniskens.eu

Window motor assembly driver side (EU)