Amp Meter Bouncing

[40phil41]

I know that this has been discussed before but of course I didn't pay attention . Yesterday we took the '40 on a 105 mile round trip to a Friday night cruise. The car ran perfectly. With an 86F outside temp. it cruised at 57 m.p.h. with an engine temp. of 160 (<170 after coming to a stop), oil pressure of 45 psi and a gas gauge that wouldn't move off full (an issue for another day). The only real issue was the amp gauge which continually bounced erratically between +ve and slightly below -ve the whole trip. I have a new regulator and coil but a generator of unknown history. What is the most likely cause of the bouncing needle and/or what diagnostics can I run?

Phil

[55 Fargo]

I know these needles can bounce a bit, but going to discharge while driving, then to show charge, is a little strange. All of the connections are good,you mention the genny is of unknown origin, so maybe it requires testing.

Actually, I will reserve comment, as I am not knowledgeable when it comes to the old genny/reg systems. I always think if mine fails, i will replace it with a GM single wire alt.

Glad the cruise was a success, at 57 mph how does it sound, are you running a 4.11 diff in there, any idea what gas mileage you are getting.........sorry I wasn't much help Fred

[Plymouthy Adams]

I think I would pay close attention to your terminal connections...be sure nothing is loose on the amp meter post, ignition switch posts and not to forget the generator and regualtor wires also..about the only other thing comes to mind is that the generator brushes are either worn to the extreme or sticking a bit in their slides and the turning of the generator is causing them to move slighly in the slide but not coming back to the commutator quickly. Brush wire psot within the generator could be loose also.

[40phil41]

I know these needles can bounce a bit, but going to discharge while driving, then to show charge, is a little strange. All of the connections are good,you mention the genny is of unknown origin, so maybe it requires testing.

Actually, I will reserve comment, as I am not knowledgeable when it comes to the old genny/reg systems. I always think if mine fails, i will replace it with a GM single wire alt.

Glad the cruise was a success, at 57 mph how does it sound, are you running a 4.11 diff in there, any idea what gas mileage you are getting.........sorry I wasn't much help Fred

Fred,

I have an OD transmission with those 4.1 gears :-). OD is working fine. Just didn't want to push it. Don't really know what the gas mileage is. Haven't checked.

Phil

[Normspeed]

I'm with Tim on this, double check all connections including the ones at the ammeter. I would also suspect the regulator itself. Even if it's new, do you have another that you could swap in temporarily?

[40phil41]

I'm with Tim on this, double check all connections including the ones at the ammeter. I would also suspect the regulator itself. Even if it's new, do you have another that you could swap in temporarily?

Yes I do have another regulator that I could use. I'll check out all connnections first, then the regulator, then inspect the generator internals. May not be until the beginning of the week before I can get to it though.

Thanks everyone for all of your suggestions.

Phil

[mikemaker]

I'm no auto electric expert, but each time my P15 has exhibited that type of behavior, it has been the regulator at fault. I'd swap it out first thing. Then start chasing down other problems if the bouncing persists.

[norrism1]

You might want to "Polarize" the genny. What do you think guys? It could make the needle jump around or I could be thinking of something else!

[40phil41]

You might want to "Polarize" the genny. What do you think guys? It could make the needle jump around or I could be thinking of something else!

I did polarize the generator when I installed the new regulator last year. Used the following which was kindly posted by someone on this forum (sorry, can't remember who).

Phil

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[Uncle-Pekka]

First I have to issue a disclaimer: Alert - The undersigned is freshman & rookie on 40's Mopars, had one for some months now.

However, I'd like to share a similar experience. Ammeter in my D24 was bouncing like you told your did and gave a high "BING!" sound while it did so. I found the reason right away by the smell: There was a short circuit in wiring, starting melt an insulation cover on a wire. Fortunately I lost only one wire under the dash and another from dome light to door post switch. The bad spot was near the dome light.

Thus my advice will be; Check the wiring, there may be a short circuit somewhere.

[40phil41]

First I have to issue a disclaimer: Alert - The undersigned is freshman & rookie on 40's Mopars, had one for some months now.

However, I'd like to share a similar experience. Ammeter in my D24 was bouncing like you told your did and gave a high "BING!" sound while it did so. I found the reason right away by the smell: There was a short circuit in wiring, starting melt an insulation cover on a wire. Fortunately I lost only one wire under the dash and another from dome light to door post switch. The bad spot was near the dome light.

Thus my advice will be; Check the wiring, there may be a short circuit somewhere.

All of the wiring is brand new 2 years ago. However, having said that, I will check out all of the connections to make sure something hasn't come loose. That is, after I switch out the regulator first. Haven't got back into the garage yet. Oops, that's a little white lie. I have been in the garage but working on my '65 Corvair :-). The CORSA International Corvair Convention is coming up in Detroit the last week of July.

Phil

P.S. No 'bing' sound from mine.

[vanbuskirk]

One of the 3 bolts to the fenderwell is a ground. I have twice solved the jumping needle problem by tightening the grounding bolt. Bob

[40phil41]

One of the 3 bolts to the fenderwell is a ground. I have twice solved the jumping needle problem by tightening the grounding bolt. Bob

Bob,

This is a new one to me. Can you please describe specifically which bolts these are and what the 'grounding bolt' is actually grounding. I may have missed something when I re-assembled the car.

Thanks,

Phil

[55 Fargo]

DIDO, I would like to know, as when my car is running and charging the needle tends to bounce a little, thought it was normal Fred. Any idea which fender well is the one with grounding bolts, the drivers side I would imagine, are the bolts brass or any different metal......Fred

[vanbuskirk]

There is a metal contact that will ground the regulator, when the bolts are tightened in the 2 holes that are near each other. When the mounting bolts are tightened, these contacts are grounded. I am talking about wildly swinging needle, not normal movement. Bob

[Normspeed]

Come to think about it, Bob may have nailed it. I recall the same symptoms years ago when I did not have my P15 regulator grounded well.

[40phil41]

There is a metal contact that will ground the regulator, when the bolts are tightened in the 2 holes that are near each other. When the mounting bolts are tightened, these contacts are grounded. I am talking about wildly swinging needle, not normal movement. Bob

Bob,

Looks like I am part way there thanks to you. I removed my regulator and remembered that the firewall had been painted with the regulator (and everything else) removed. I couldn't see any 'metal contact' but I took some emery cloth and sanded off the locations where the three bolts go into the firewall. I did notice that the nuts are captured nuts on the firewall and are very loose. Nevertheless, I re-installed the regulator making sure that the three bolts were good and tight. The result - now when I am at speed the alternator stays perfectly still just at '0' (actually less than 1/2 the thickness of the gauge line towards +ve). However, when at idle it still makes large swings. As long as the engine is at a speed higher than idle it steadies out. I think that based upon this partial success I will add a ground wire fron one of the bolts to a good ground and see what that does.

Thanks again for your help.

Phil