1976 Convertible Power Window Problem

[pulteney]

Two weeks ago, my left rear window would raise only if I cycled the driver's armrest switch several times. When it did work, it was normal speed with no hesitation or binding. I optimistically assumed it was a switch problem and postponed fixing it. Bad idea. Today, neither the front nor rear armrest switch will raise the window.
As all other windows worked fine, I pulled the trim rear panel and started troubleshooting from the motor end of the circuit. There is 12 volts at the appropriate motor connector wire (green - up / purple - down) when either the front or rear switch is actuated. That just leaves the connection to the motor, the motor itself  or the ground. With fingers crossed, I cleaned the connections. No luck.
Is there anything else I can do before starting the rather daunting task of replacing the motor? The Fisher Body Manual shows that it is not a trivial procedure and has safety issues. One of the first steps is to place the window halfway up. How do I do that if the motor is inoperable? Also, in a search online and at the local NAPA dealer, only front left & right motors are listed. Are the rear ones different?
Either the Fisher Body or the Workshop Manual mentioned an internal circuit breaker in the motor. Is that a thermal CB or is it manually resettable?
Any help will be much appreciated,  J Ball

[76eldo]

These motors are pretty robust and luckily I have not had one fail on any of the cars I had owned.
There were so many GM converts made from 71 to 76 that would use the same motor, I would think its available. Hydro Electric in FL would have them.

If you have any good auto glass shops in your area, they might be able to replace the motor for an hours labor. You already have the motor exposed so maybe take to a shop and ask them to just do the window motor and you will put the rest back together.

The older I get, the more I am willing to pay someone who is a specialist in certain things.

Look for a shop that's been around for a while and ask if they have a tech that knows these cars.

Good luck.

Brian

[TJ Hopland]

The rear motors are different than the fronts but I believe they also fit some other GM cars so they were not that hard to find.  They were not super common but they seemed to be out there.   I also believe the motor section was the same it was just the gear section and mounting that were different so it would likely be possible to swap the motor section if you had to.   

Its been a while since I messed with this era motors but I seem to recall that they do work by being grounded through the body.  I could be remembering wrong.  I know I ran into that on some 70's or 80's car.  The motor would not work off the car but worked fine in the car.  I remember being really puzzled by that at first because I thought it only needed the 2 wires but it was actually a sort of odd field series shunt design.  I may have that terminology wrong, like I said its been a long time.  Just throwing it out there. 

[cadillactim]

I don't have a parts book handy, but if memory serves me correct, the rear motors are like the front ones. Of course there is the LH and RH issue (LH on front door may be the same as RH on rear 1/4, would have to verify first).

The circuit breaker is inside the motor, and is heat activated. It only shuts power off when overheated. Once the circuit breaker cools off, contact is made again. These rarely cause a problem.

The motor is grounded through the body. Try unplugging the connector and applying battery voltage directly to each of the two connectors (one up, other down). If the motor doesn't run, it is bad.

It's been a while, but I've taken the motors out without a lot of difficulty. You can unbolt the regulator, then the motor/regulator assembly will  move. Then you can slide the window rollers out of the regulator guides.  Then you can pull motor and regulator out of car. I recommend removing the motor and regulator together, then remove the motor from the regulator out of the car.

The safety issue is the return spring on the regulator. If you pry the motor off the regulator in the car, the regulator can "snap back" and sometimes the spring can fly off. Once you have the regulator out of the car, simply place it on the ground, put your foot on top of the spring with some pressure. Unbolt the motor, pry it out of the regulator with your foot still on the spring. Once the motor is removed, then gently let pressure off the spring and the regulator will gently "unwind."

I have reconditioned motors available if you need one.

Tim

[pulteney]

I believe that I have solved my intermittent power window problem.
After resigning myself to replacing the motor, I decided to recheck my testing procedures one last time. I realised that I had always used battery voltage (engine off) to troubleshoot the system - 11.8 volts at the motor connection. Since all the other windows worked fine with that, it sounded reasonable to me.
After starting the engine and thus supplying another 1 1/2 to 2 volts from the alternator, it worked!
So, either the motor is weak and requires a little more voltage than the other three or there is a poor ground, probably between the motorcase and the chassis. To ensure a good ground, I have placed a jumper wire from the case to the chassis. The window zips up and down very nicely now.
Just in case I am a victim of coincidence, I am leaving the interior trim and access panel off for a few days until I get more confidence that the problem has been fixed. Aren't intermittent problems the pits?!!

[RobW]

Glad to see you got it working.
But in case anyone else needs the info, I dug out my May 1979 Motors Crash Book to look up the part #'s.
For 71-76 Eldo:
Motor rear 4999680 and 4999678
Motor front 4999680 and 4999678
Same part #'s for 74-76 Deville/Fleetwood, 77-78 Eldo, 71-73 Deville/Fleetwood.
So 71-78 Calais, Deville,Fleetwood, and Eldorado all the same. Only thing is Left or Right. Front and rear are the same on the same side.

[pulteney]

Thanks everyone for the great technical help! You have lived up to your reputations.

[TJ Hopland]

Guess I have a car with a wrong motor in it then.   I do remember having a motor problem and thinking I could swap front and rear but when I got the trim panels off saw they were different so IIRC I ended up doing a quick repair job by swapping the motor sections on the problem motor and putting it back.   

Guess the good news is that apparently there is another GM motor that fits.  I think I may still have my parts motor under my work bench at work, I will have to dig it out and see what number was on it.  I do remember the number was stamped in orange ink on both units.

[cadillactim]

The 1976 window motors have a different wiring plug connector than the 1961-75 motors. A 1961-75 motor will work on a 1976 if you splice the older style connector.

Tim