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Since my 39 Six has a rare option, the mechanical tach takeoff from the rear of the generator, thought it would be wise to rebuild. Opened it up, tons of grease and two brushes severely worn, but no commutator damage. Replaced the 3 brushes, replaced the front bearing and rear bushing and had the commutator tested, all good. Put it all together and apart from some minor sparking at brushes (I'm attributing to new brushes seating), worked great.

Then started replacing wires to generator and regulator as they were badly fraying (original wiring) and replaced with modern cloth covered vinyl wire. Went for a long ride, worked great

Started the car yesterday and a loud buzzing frion the regulator. Noticed ammeter showing heavy discharge so shut off. Repolarized generator and seemed to work OK. After another drive, same problem.
Pulled cover off a NOS regulator I bought about 9 months ago and saw that the points to the geberator field had overheated. Replced regulator with the old regulator I had that had issues of overcharging as a troubleshooting aid, and it seemd to work fine. Went on a cruise with a charter group of teh AACA and had huge issues on return leg of trip, heavy discharge

I am suspecting an intermittent field winding causing teh polarity to get reversed as it wouyld do if disconnected from circuit

Looking at the schematic in the service manual confuses me. It says car should have a VRD regulator, this one is a VRR, as was the onbe I pulled out. Generator is a 3 brush GCJ-4810A-2 which is correct

Car had run for years with this config, possibly as long as we have owned it so looking for suggestions. Fou0nd another NOS regulator which should arrive this week but reluctant to connect as they will get ruied if field polarity is reversed

Suggestion? Correct schematic anyone?

VRR is simply replacement number for OEM VRD.

You are correct, thanks!

Ideas for this problem?

Paging Howard...Flare sent up...MayDay MayDay Howard....

I don't have any schematics other than what is on this site and the AEA diagrams at the PAC site. None are of spectacular quality but the one on this site is the factory diagram for 6, 8 and 12 cars. Since it relies on tracing numbers instead of wires and being of poor quality it is hard to read.

There is a good description of the Autolite voltage regulator and 3 brush generator on page 65 of the 38-39 shop manual which you can download from this site if you don't have one. It has service cautions and adjustment procedures.

From the description the third brush adjustment and not the regulator controls current output. From the schematic it appears to do this by limiting the amount of voltage available to the field coils thus controlling their maximum strength. The regulator controls the voltage out by rapidly cutting in and out extra resistance to the field to weaken it when voltage starts climbing. With the burned points and other issues I would wonder if that third brush is adjusted properly or could possibly be intermittently shorting to the output brush or wire and giving the field a jolt so the generator produces a burst of max current. Less likely but still need to be checked would be if the field wire between the regulator and generator was somehow intermittently shorting to ground.

Thanks Howard, that was the conclusion I was coming up with, 3rd brush or possibly even an intermittent field issue

Pulling the generator off shortly and as luck would have it, found a generator shop nearby that is very familiar with this era of generators, so if noting obvious, off it goes tomorrow. He wants it for several days, just to check it out, so must be busy and I was hoping for a thubs up "good" or down, in which case let them fix it

More later