Soldering to a commutator...

If you have reached that point... Something has gone wrong... Very wrong.

I can't see a reason to be soldering to a commutator... Why are we opening up the motor? Did something break? (Maybe there is good reason to do this, that I just don't see)

Are we talking about soldering the brushes that make contact with the commutator? If so, then a silver solder is stronger and has a higher melting temp, which would be best.


Very high temp solder is likely best, and one with a high strength is needed. The manufacturer would be the people to ask what is best... Or ask about getting a repair or warranty replacement if that is still an option.

Commutators and brushes... You are looking at a high temp and high stress area, one where soldering is likely not going to work. I have a feeling that the internals of a motor are ultrasonically welded, mechanically crimped, or otherwise fused directly together without some kind of intermediary component like a solder or welding material used.