12V DC motor repair help. Car heater blower fan.

[wilfred]

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[tpowell1830]

Do you watch Ave? This is not exactly the same but the treatment of brushed motors is Universal (hehe).

[SeanB]

Likely brushes, and check the armature for shorts or open sections. While you have it apart clean out the bushes with solvent, and relubricate with engine oil, leaving it to soak into the pores. If you can get them out put in a small bath of oil and heat till the oil is just smoking a little, and leave to cool, to draw it into the pores.  Oil the felting reservoirs as well, and polish the shaft with a cloth to get it shiny where the bushes are. Do not misplace any of the washers on the shaft, and put them back in the same position and the same way round.

Commutator clean with 1200 grit paper and then polish with the back of the paper to burnish, and leave like that after a degrease.  Assembly put a drop of molyslip grease on the shaft as lube, wipe to a film on both sides.  Brushes make sure they are free to move in the holders, and slide freely. Then put back together, apply 12V, with it held down firmly, and check it runs well and spins down without much cogging or noise.

[drussell]

SeanB is right on the money above....

Your problem is almost certainly caused by worn-out brushes.  Check the windings while you have it apart anyway, clean and re-oil-impregnate the Oilite bushings (they are usually just those bushings rather than full roller bearings) and it should run fine for another decade or two.