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Why does banging on window regulator motor fix it?

My window doesn’t work. I opened the door panel and whacked on the motor. Window started working. Then it stops working. Banging again makes it work.

What exactly is going on here? Is a gear in the motor stuck? Or am I shaking a loose connection back to live? How does banging actually make the motor work?

The commutator on the window motor is probably worn. This causes a poor fit against the brushes and whacking the motor causes a better fit; although it’s temporary.

The situation would be the same as a worn starter motor that will start working again after being whacked briskly with a hammer.

I Doubt Your Regulator Motors Are Similar, But On An Intrepid I Was Able To Remove 2 Screws (Caged Nuts) And Slide The Motor Can (With Magnets) Right Out, With The Regulator Still Bolted Firmly In Place.

I cleaned the brush contact area, inspected the brushes and put it back and it worked. I could lightly pull the brushes out (against their springs) by their pigtails so the shaft (with pinion gear) would go back in. I did this with window fully closed.

The whole job, including trim panel R&R took just minutes.

CSA

OK and CSA’s posts are dead on but I will add that most automotive 12 v electric motors use brushes on a commutator and the mica that separates the lands will get smeared across the lands when they wear down. On starter motors an old hack saw blade will easily clean the mica but on smaller motors the cleaning can be tedious and re-installing the armature can be very difficult for the amateur. My hat is off to you CSA. I have cleaned old Lucas wiper motors with success but it was a PITA.

Check the “cut away mica” picture.

If one wanted to go so far as to start undercutting the armature commutator, due to the much smaller non-hacksaw friendly size one could visit a hobby or craft store and buy a razor saw.
They’re about 5 to 7 dollars near as I can remember.

I’d just replace the motor if the car were mine.

rockauto.com will likely have the parts you need for a decent price. Worked for me.

The brushes sit in a cage and sometimes they stick inside the cage so they lose contact with the commutator. When you hit the motor, the brushes are jared loose and the spring pushes them in place. The motor works until the brush(es) wear down a little and lose contact again.

If the motor has been used a lot, the ends of the brushes wear at an angle which causes them to cock on the cage, this is one source of them sticking, the other is that sometimes they just don’t fit. Also, as they wear down, the spring puts less pressure on the brush to hold it against the commutator.

Banging on the window motor doesn’t fix it. It just gets it going for a little longer. If banging on it would fix it, you’d only have to bang on it once and it would work forever.

Like the others have said, the internals of the motor are wearing and sometimes the motor needs a little impact to get it rolling again. Time for a new motor.