Erratic ammeter (not Model A)

[dave11]

I have a 31 Plymouth that has an issue with the amp gauge. At an idle it behaves fine, once the engine is up to operating speed the needle swings back and forth from charge, about 8 -10 amps down to zero. The charge system is very similar to a model A, 6 volt positive ground generator. Adjustable charge rate with a cut out.

Dave

[Jim Brierley]

Make sure all terminals are clean and tight and gen and is grounded. Also try a different amp meter, need not be permanent.

[mantta]

A dirty comutator or worn rushes will cause that.

[SeaSlugs]

Originally Posted by mantta

A dirty comutator or worn rushes will cause that.

yup- or bent shaft.

My guess and the most common is either A worn bushes or B stuck brushes from carbon buildup or C broken tension springs.

I'm assuming it has a band covering the brushes. you should see how much life is left in them, if they look healthy (not too worn or cracked) blow out the generator with compressed air and focus on the brush holders. If it still looks extremely dirty get a can of electrical contact cleaner from any auto parts store (sometimes called electromotive cleaner) and liberally spray out the brush holders. use a small screwdriver or pick to hold the spring tension off the holder and ensure the brushes slide freely in the holders. Then give it another whirl.

And yes clean the grounding path and check electrical connections from generator to battery to ammeter.

[Tom Wesenberg]

Dirty or loose connections anywhere in the charging circuit
Worn brushes
Weak brush springs
A generator commutator should have the insulating material undercut about .010"

8 to 10 amps is too high a charge rate.

[dave11]

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Thanks for the info Gentlemen

Dave

[SeaSlugs]

I know its a Plymouth but can we get a pic? That and keep us updated on what you find. Cars of this era are pretty close to one another when solving problems.