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  1. #1
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
    Join Date
    14 Aug 2010
    Medford, MA
    '90 900 LPT with a flat-nose conversion

    Resurrecting Dead Power Window Motors - C900

    I am telling this tale of how I fixed a "dead" power window motor because I have seen nothing else like it on the forums, and because the only solution to a bad motor that I have ever seen suggested is getting one from a scrap SAAB or Ovlov, or spending an exorbitant fee to get a remanufactured one. Let this be a sort of last hope for any poor window motors that may be wrongly pronounced dead.

    Difficulty: 1/5

    Tools Required:
    -A Torx driver (one in the trunk probably works)
    -All tools needed to remove window motors as per FixMySAAB's tutorial.

    Parts Required:
    -Some grease
    -A piece of wire
    -Solder (optional)
    -Silicone caulk (optional)

    It all began on a stormy day on my way to visit my grandmother. I had the windows down because I love breathing the heavy, humid, rapidly cooling air an approaching Midwest thunderstorm brings. When I got onto the freeway, I hit both the window switches, expecting them to close. Driver’s side did. Passenger’s side…did not.

    I stopped in a supermarket parking lot and quickly pulled the door card, detached the window glass from the mechanism, and shoved the window up, jamming it in place with a conveniently-sized snowbrush I had in my trunk. I bolted the door back together and grandma did not get a chance to deride my car, as she is so fond of doing.

    When I got home, I pulled everything and set about diagnosing the problem. Due to the sudden nature of the failure (window had been going up and down just fine all throughout the day before heading to grandma’s), I assumed it must be electrical. A quick voltage test at the door proved that electricity was getting to the connectors. A bench test of the motor produced various hummings and clickings from within, but nothing to speak of.

    I assumed the motor must be gummed up or mechanically jammed, per the other FAQ’s and fixmysaab.com. For all I knew, these SAAB power window motors just failed like that. I duly took the advice of everybody and disassembled the motor.

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    I found virgin grease and a freely-moving geartrain. I oiled and greased the thing some more for good measure, and after more bench tests I couldn’t get the thing to do anything more than a very jerky, stuttery 20rpm at the worm gear—translating into a quarter turn or so of the pinion in one minute. How could it fail so suddenly?

    I decided that maybe my 12v power source, a little black transformer box from a telephone answering machine, perhaps wasn’t enough to turn the motor. So I went for bigger guns. I connected it first to the window leads and tried the switch. No go. One click issued from the motor, and then nothing. I then ran leads straight from the battery to the power window motor. Again, it issued one click and maybe 1/8 of a turn of the worm gear for each time I connected it.

    The thing actually worked better when connected to a wimpy answering machine power source than when connected to good DC 12V! It confounded me.

    So I figured I was going to have to somehow procure a new motor or else go to crank-windows. In the name of investigation and because I had nothing to lose, I took the motor apart further. I got the brush carrier out and marveled at the well-built armature and bearings. Despite being in constant use for 22 years, everything looked like it had just been built yesterday. Nothing appeared broken. The brushes were fine, but what on earth were those coils and little black thingy for?

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    Me, taking the actual motor off of the geartrain

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    The motor, sliding worm gear out of its place

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    The brush carrier, with brushes, coils, and "black thingy" (later found to be circuit breaker).

    Feeling frustrated, I left it for some days. My makeshift repair with the snowbrush was holding the window up just fine. I exhaustively searched the forums for anything having to do with power windows, and I found obscure, furtive mentions of a self-resetting circuit breaker within the motor to prevent overload.

    AHA. “That must be what the black thingy is,” I thought to myself. I wired a bridge across the two leads of the black thingy and tested the motor using its original leads from the door. To my delight, it spun so fast it flung grease everywhere.

    I believe what happened is that the circuit breaker (black thingy in photo) passed the end of its service life and got very sensitive, so that any current at all would trip it. The motor thus wouldn’t turn more than the little bit of current that got through the circuit breaker could make it turn. The reason it was working better with the 12v power source was because it had to convert from AC to DC using an inverter. I remembered from playing with an oscilloscope as a child that inverters converting from house current produce DC with a subtle pulse at 60hz—just enough of a dead spot to reset the circuit breaker, 60 times a second.

    I made my wire bridge permanent and covered it with bathroom silicone to prevent wires from shorting on the metal case (one of the few acceptable applications for this substance on a SAAB, I know).

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    My repair. I know it's hard to see, but I didn't think to take a picture until I'd gummed silicone all over it. Basically, what you are seeing is the other side of the brush carrier, in its installed position. Under the white silicone caulking is a wire twisted around the two terminals of the "black thingy" (circuit breaker) to effectively bypass it. The terminals poke out into the worm-gear side of the motor, so you don't even have to remove the brush carrier from the motor to perform this repair.

    I put the thing back together, freed up and greased the raising and lowering mechanism, and my windows have worked fine since. The only problem with this little repair is that caution must be exercised when rolling the window up or down. It won’t stop for anything short of a blown fuse now.

    However, in my personal opinion, the circuit breaker does more to protect the motor than it does to protect fingers or n’importe-quoi that gets into the way of the window. Windows with motors equipped with circuit breakers can hurt you just as bad, and the fuse in the fusebox will prevent fire hazard if you keep giving current to the motor and the window is stuck. With a bypassed breaker, you could possibly fry your motor if the window’s iced shut and you’re holding down the button, but if you’re smart enough to be able to hotwire the motor and gum it up with silicone, then you’re smart enough not to do that. Besides, it’s not like you’re going to lose anything more than a window motor you previously thought was unsalvageable

    One final word of advice. DO check to see what else is gummed up before you hotwire the circuit breaker If other things are wrong with the drivetrain, they could be contributing to the slow window, and likely overload on the circuit breaker that contributed to its failure.
    Last edited by euromobile900; 15 January 2011 at 04:06.
    Ask me a question about your c900! I promise I either can answer it or know someone who can



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