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The windows on my car were real good until a couple of weeks ago then the drivers side window started running slow. last weekend I took it to a car show about 90 miles from the house. Putting the car away I tried to put the windows up and got nothing on the drivers side. I am assuming that the motor went bad. I noticed in looking for the part that there are a couple of different options. Motor with or without gear. I can get the one without from a local parts store in a couple of days or order the one with the gear from a catalog and wait up to a couple of weeks. How hard are they to change and is it worth the wait and the extra $40 to get the gear.
First try to see if the motor works. Take a jumper wire and bypss the switch. You can also get a test light to check for power at the connector. If you do not have one they are simple to make.
Unlikely that the motor has gone bad. It is possible that the brushes in the motor are worn out. But, it's more likely that the switch for the window has carboned-up contacts so adequate current can't flow to run the motor. Your 'clue' about running slower recently leads me to this conclusion.
mine did the same in my 1980...after replacing the switches, pw motor and going through he**, since i'm not a great mechanic, i traced the wire back through the door and found it had split inside the door jam...spliced it together and i was in business. good luck...rs
Same thing on my 76. While I had the door open I moved the rubber connection between the door and jamb while working the switch. One of the wires was cut. I ran a new wire and it had has been okay since.
Move the other switch to the side which does not work to see if that fixes the problem. Just takes a couple minutes. If it is a bad switch, vendors have them for $12 to $20.