Vacuum motor arcing from one brush
I have a 1970s vintage Hoover Celebrity III (model S3123) vacuum that has given me good service since new. Recently it started making a grating noise when the motor was spinning down after use, so I tore it down for a look.
This is a universal (brushed series wound) motor. I found that the felt oil donut was dry. The bushing (Oilite?) was badly worn, to over 1/2" ID at the bottom for a 1/4" shaft. The armature showed signs of having hit the field pole pieces.
No parts seem to be available for this motor, and I couldn't find an equivalent bushing. This one has rounded shoulders, probably so it can rock a bit in its holder. I bought a 5/8 x 1/4 bushing, drilled out the existing bushing with a 5/8" bit, and pressed the new bushing into the old.
When I test-ran the motor after reassembly, I noticed a lot of arcing from one of the brushes. The other one just has light sparking now and then, but this one has a constant arc. Sometimes the arc even wraps across 2-3 commutator segments. That can't be good.
Also, after the motor had run for maybe 15-20 seconds, it sped up slightly and the arcing diminished (but didn't stop).
I don't know whether the arcing was happening before the rebuild, as I didn't run the motor where I could see the brushes before tearing it down.
The brushes seem to have plenty of length left, and only one is doing this anyway. Could it be insufficient brush spring pressure? The culprit brush doesn't feel like its spring is weak, but I don't have a scale or any other way to measure the actual tension.
I don't think I swapped the brushes in reassembly - the field connection to the one only allows it to fit where it's supposed to.
Is there anything else that would cause one brush to arc that bad? Anything I can do to stop it? I hate to give up on this good, solid steel US-made vacuum cleaner. Besides, I have a stack of spare bags in the drawer for it. :)
Here is a link that might be useful: This looks similar to my motor (scroll down half way)