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Generator Question for '40 Special.


Victor W
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So question on  charging system fault finding. I have '40 Special where the charging system quit working. Was working fine (had replaced the VR) when one day the ammeter showed it was dead. 

 

I did the motor test to the genny ( hooking the genny straight to the battery) and it spins up like it should. Is that a valid test for genny? I don't have a growler and the manual is not very helpful on genny tests.

 

I'm still suspecting the genny ad the VR is new. I tried grounding the field terminal with no change. Double checked my grounds and all the other wires and am a bit of a loss.

 

So generator motor. Validation the genny work or?

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With the engine running, briefly ground the field terminal and see if the generator goes to full charge (ammeter should be pegged on the + side). Then you know whether it's the generator or the regulator that's broken. New regulators aren't terribly reliable so just because it's new doesn't mean it's working properly.

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If it passes the motoring test, there is a high probability the generator works. With the engine at something above idle, grounding the field should make the generator charge.

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Just a quick note about the test @Matt Harwood is talking about...  If the cutout relay in the voltage regulator is not energizing, the full field test Matt describes will not work. The reason is that if the cutout relay is not energized the armature of the generator is not connected to the rest of the electrical system and therefore the amp meter will not show the charge even if the generator is working just fine. The next test should be to measure the voltage from the armature terminal (the large terminal) of the generator to the case of the generator with the field terminal grounded and the engine running above an idle. It should be over 6 volts. If it is then the voltage regulator or a connection is bad. Let us know what you find.

 

Also, NEVER assume that because a part is new that it has not failed!!!!!!

 

 

 

Edited by 37_Roadmaster_C
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Victor:

Very important question.  The 1940 Buick generators are much larger than the 1937, 1938, and 1939 Buick generators and the 1940 Buick 6V voltage regulator must match the generator.  When you replaced the 6V voltage regulator, did you replace it with the correct one to match the existing generator?

Lawrence

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Status update. Ran a few tests and while leaving the field coil terminal on the VR grounded the generator started to work. Puts out 8 volts at full tilt. I had done that test before but it didn't work. One difference was I left it on until I saw the change. Continued charging after I disconnected the jumper. I'll keep monitoring but I think something is still suspect.

 

The VR was from CARS. I asked for the '40 model and assume it's right as it resembled the old one. I've checked all my grounds (genny to block, block to battery, battery to body, VR case to body) and they are all good.

 

What's more likely to be intermittent, the generator or the VR?

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4 hours ago, Victor W said:

What's more likely to be intermittent, the generator or the VR?

 

I would suspect the VR first, however, it's possible there's something going on with the armature windings or commutator.  How do the brushes look?  Brushes (or the holders) can get dirty and 'stick' such that they don't reliably keep the brush in contact with the commutator.

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I have been reading this forum for years, and have still not seen a single instance posted where one of those "new" regulators worked properly. I've not tried them myself so cant say for sure, but the track record certainly does not look good. Do you still have the old one? I would try it if so. The old ones were generally repairable.

 

An intermittent field is pretty unlikely. Most generator problems are worn out or sticky brushes. The only way to tell about the brushes is to look at them. Does this generator have a removable band?

 

I'll place my bet on regulator trouble.

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Thanks guys. The brushes are what were in the car when I bought it. They look fair but I probably should throw a fresh set and new bearings in it. Might see if the local old tractor shop can look at the armature.

 

The old VR was not serviceable. The previous owner had hooked the wires off the generator wrong. The current from the armature circuit literally melted the field coil wires. It was toast. 

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Update to my previous update. I'm pretty sure its the VR. If I jump the field coil to ground it starts charging and stays that way if I'm running. Shut it off and it reverts to no charge until I jump it again. Odd failure I've never experienced but I guess. 

 

Anyone have source for a VR they recommend other the usual suspects (Bobs, Cars.Inc)?

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If it were me I would look for an NORS or used one on ebay. Make that NOS if it has to look correct for shows. Yes it may require a little tweaking. They don't usually wear out, but may need adjustment, or some very gentle cleaning of the points.

 

The whole setup procedure is in the shop manual, and requires a generator test set, which most people don't have. Fortunately most regulators don't need a whole setup. The settings on the cutout and the current regulator almost never need changing as long as it is the correct regulator for the application. The charging voltage might need adjusting. On an NOS or NORS regulator that hasn't been used before, even the charging voltage is likely to be OK.

 

If you have a digital multimeter, and if it can read the battery voltage while the engine is running and system is charging, without locking up or getting all confused, then you have what you need to check the charging voltage.

 

It can be hard to figure out which of the regulators all over ebay might be the right kind, because the aftermarket manufacturers all had their own part numbers. A good place to start would be with the Buick and/or Delco part number. I'd look it up but don't have the right book nearby. Maybe someone else in here can look it up. Another idea might be to check with Dave Tachney about a used one.

 

 

Edited by Bloo (see edit history)
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  • 5 weeks later...

I wanted to provide a final update as to what fixed my charging issues. I hate threads left hanging with no resolution. 

 

It was the VR. I ended up with a reconditioned Delco Remy off of Ebay. Charging working as needed now. Took the cover off the new failed unit. No obvious sign of failure but I suspect the field coil is sticking somehow.

 

I'll post a new thread of I find the obvious cause.

--Victor 

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