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Diagnosing bad motor

noquacks

Jun 26, 2013
127
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Jun 26, 2013
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People,

Have a 12v dc motor which operates a car headlight door (1987 Sunbird GT). I applied 12v directly from battery and it does not respond. Here is a link to the exact type of motor:

https://www.ebay.com/itm/313783539539?chn=ps&_trkparm s=ispr%3D1&amdata=enc%3A1rTenDbvlR4e-Zm19dRAHUA94&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=313783539539&targetid=1644837435243&device=c&mktype=&googleloc=1015197&poi=&campaignid=16743749222&mkgroupid=138744546207&rlsatarget=pla-1644837435243&abcId=9300842&merchantid=426122391&gclid=Cj0KCQjwmdGYBhDRARIsABmSEeP1UeSxh7hpoN89hWsRx1KIXg1WWK8ykpL6Fyb7tl6hJdFgqmGg-rMaAmiIEALw_wcB

Where would one begin in determining exactly what is the culprit with a no start/run motor? Brushes? Commutator? Other? I have no such experience, but am willing to try.
Thanks.
 

Minder

Apr 24, 2015
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Apr 24, 2015
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3,479
Firstly i would separate the motor from the gear-box and see if the motor is free to turn.
Then check continuity across the motor leads and also try a power source with the GB removed.
One of those procedures should turn up a possible reason.
 

noquacks

Jun 26, 2013
127
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Jun 26, 2013
Messages
127
Firstly i would separate the motor from the gear-box and see if the motor is free to turn.
Then check continuity across the motor leads and also try a power source with the GB removed.
One of those procedures should turn up a possible reason.

Thanks, minder. Good tip to start with. So, I popped offf the lower gear wheel, and applied 12v DC from the car battery. The motor did turn, which I was happy about, but man, what a loud screeeech. Yikes. What would cause that, and what to look for next to resolve the screech?
 

noquacks

Jun 26, 2013
127
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Jun 26, 2013
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127
Dry bearings?
How free is the shaft to turn?
Is the motor removed completely?

OK, I will remove the motor which is royal pain as it is so difficult for these motors to drop back down between the 2 carbon "magnets". Guess I have no choice, so here it goes.......
 

noquacks

Jun 26, 2013
127
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Jun 26, 2013
Messages
127
OK, I will remove the motor which is royal pain as it is so difficult for these motors to drop back down between the 2 carbon "magnets". Guess I have no choice, so here it goes.......

Shaft does turn freely, with squeak, for the record.......
 

noquacks

Jun 26, 2013
127
Joined
Jun 26, 2013
Messages
127
Opened it up, and so much gunk inside. Cleaned it up with brass brushes, solvent, etc. Applied some oil in key spots, and had help holding back the brushes to drop the commutator back in. Now motor spins great! Clockwise, and also c-clockwise, as these motors spin both ways.

Now, after installing it in the car I have a bigger problem- the headlight actuator dos not respond to the light switch in the cab. So I have to troubleshoot the circuitboard. I repaired this a while ago with the help of members here, so be on the lookout for me and this project soon!

Thanks, people.
 

kellys_eye

Jun 25, 2010
6,514
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Jun 25, 2010
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6,514
The fact that the motor was seized would very likely cause the supply fuse to blow so that would be the first thing to check. If someone put in a higher rated fuse (unsurprisingly this is a common practise even though it's completely wrong) it may also have caused the operating switch to burn out. Worst case would be a burned out cable.
 

Bluejets

Oct 5, 2014
7,053
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Oct 5, 2014
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7,053
Check for dead relay...just about everything in autos is under relay control, especially motors.
 
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