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1934 Chevrolet Electrical Problems


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Some of you may be familiar with my 1934 Chevy DC Standard 3-window coupe. It is a 95% original car rescued from 57 years of storage, refreshed mechanically into a nice driver with total preservation of its 85 year old patina. I have described my brief ownership in the Restorations and Our Cars forum but now that some electrical issues have come up I want to start this technical thread so that it may help me and others. I've worked on just about every part of a car over the last 55 years and for the most part have been satisfied with the outcome and the knowledge I have gained through the experiences. The one exception to that general satisfaction has been electrical problems. No matter how many time I read the manuals and run the tests it all still seems like magic that I just don't get. So as we get into this please remember that and speak slowly and distinctly...

 

When I first got the car everything worked fine. During the PO's refurbishment some new wiring had been added but most was original and is in good condition. He added all new heavy gauge battery cables with a disconnect and converted the taillight to LED for increased brightness, leaving the headlights as original. I replaced the battery and keep it charged with a Battery Tender. The car starts easily and when driving the ammeter would show a charge around 10 amps then drop to zero when idling. Almost a month ago I took it for a Sunday drive and noticed that the ammeter did not show any charge while driving but rather just under zero and dropped to a small discharge at idle. I charged the battery and checked all the connections at the battery and generator. Fully charged the battery voltage read 6.36 and with the car running and revved up it read 6.23. At this point I started posting in my other thread, searching and reading on other forums, and talking to car buds. Next post will be what I found out. 

 

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A good generator shop could check your generator output and set the regulator or cut out.  Knowing both those are in speck will  good  and be a place to start.  It;s not Rocket Science but  requires a basic knowledge of the different problems which might occur.

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So the first logical thought was a defective generator or cutout. I started the car up then disconnected the battery, the car died confirming the no charge. The cutout on mine is an older Niehoff replacement, I pulled off the cover and it looked new inside. The points were not stuck but I lightly sanded them and sprayed electrical cleaner - no change. I checked output at the armature wire (GEN side of cutout) with the engine revved up a bit - 0.37 volts. Then I checked the BATT side and got 6.36 volts, battery voltage only. I opened up the generator and saw it was clean inside, had a shiny commutator and newer brushes. At this point I got distracted by some of the  advice and opinions I was getting and started looking at wiring fuses, under the dash, etc. all of which told me nothing. I had at first dismissed the factory shop manual because like many from that era it assumed a great deal of knowledge on the part of the mechanic and left most of the detail out for modern dummies like me. But I went back and re-read it carefully and found a simple test I had missed - clipping a jumper wire from the GEN to the BATT terminal and bypassing the cutout completely. I did this and immediately got my charge back on the ammeter, the car kept running with the battery disconnected, and the output now reads 7.6 volts.

 

So, it appears that the cutout is my problem, which is what most other comments and data supported. While all this was going on I bought a generator core from bearsfan315 on here which includes an old Delco Remy cutout. When it arrives I will check it out and if it looks decent I will swap it over and see if it works. If it does not, some questions:

  • Am I better off getting an old mechanical cutoff rebuilt or buying a new replacement?
  • I have gotten many comments about replacing the mechanical cutout with a "diode" electronic replacement either converting an old unit or buying all new. What are the advantages and disadvantages of going this route?

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Hello,  I am not a expert but do have a working  knowledge of basic generator circuits. In the early days a cut out was used. This was a relay that when the engine was off the points were open. If they stuck close the battery voltage would drain away through the armature. The relay has two coils, a weak and a strong one. When the generator starts spinning the voltage pulls close the points through the weaker coil.  This allows the battery to be charged.  As the battery voltage increases it pulls in the stronger coil which then opens the points until the battery voltage no longer hold open the points  then they close again until the battery becomes charged again.   A generator shop can set the coils to the proper specs if a replacement relay won't work out of the box.

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The diode modification is essentially creating a switch similar to the contacts on the cut out.  When the generator voltage exceeds the battery voltage the diode will allow the generator to send charging current to the battery.  If the generator voltage is less than the battery voltage, the diode will be reverse biased which means it will block the battery from sending current back into the generator and discharging.

 

Your wire together will work as long as you remember to remove it when the car’s not running.  A wire is an always “ON” switch in this application.

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You could put a manual switch in temporarily to drive the car, if you forget it on, the generator turns into a motor, and your battery goes dead fast. 

 

When you are testing by removing the battery from the circuit the voltage goes to the output of the generator, so say 10V if it is set high, it will take out any lights that are on.  I would leave the battery in place and test with a multi meter, anything over what it reads not running will show it is charging.

 

There are lots on ebay, https://www.ebay.com/itm/VINTAGE-N-O-S-1920s-1930s-GENERATOR-REGULATOR-RELAY-1929-1930-1932-1935/124292562987?hash=item1cf06a002b:g:JrQAAOSwZ11etY6u

 

Brillman sells them also  https://brillman.com/voltage-regulators-cutouts/

 

You can still get them at NAPA  https://www.napaonline.com/en/p/BK_S68375  a little black paint it will look great.

 

 

DFeeney is correct if the cut out switch is set too high (above your 7.6 charge rate) the switch will not pull in the connection.  So it could be working correctly just not set correctly.

Edited by Graham Man (see edit history)
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Diode failure is common......go to Brillman and buy a new cut out for twenty bucks, paint it black, and your done. They look better than your current cut out. They sell the solid state units also. They are very reasonable.......I carry two of their modern units in every tour car to get by in the event that the original goes bad. You can just charge your battery and drive it with a bad cut out.......the ignition uses very little power. Many people on tour who have a generator go bad just charge their battery every night to get through the tour. 

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Edited by edinmass (see edit history)
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Don't bypass it. It's there to keep the generator from getting damaged. Some people like diodes because they have toruble with the mechanical cutouts sticking. Cutouts can stick, but the most common failure of a silicon diode is a dead short, and that would have exactly the same effect, so that route never made any sense to me.

 

If it were the original I would be in favor of having a go at repairing it, but it isn't. I'm with edinmass, just get a new one. I vote for mechanical.

 

Or, maybe someone over on the VCCA forums would have a correct one......

Edited by Bloo (see edit history)
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Check fleabay and other sites for "Delco 1867781" which is the number which supersedes all the 265-series (and other) 6V cutouts.  The 7-digit Delco numbers came out about 1937-38.  It was used, I believe, on junior 1939 Chevs with 3-brush generators and even on Mercury Marine engines.  It's been 10 years since I bought one that way but it was *then* quick and easy to find.

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17 hours ago, edinmass said:

Diode failure is common......go to Brillman and buy a new cut out for twenty bucks, paint it black, and your done. They look better than your current cut out. They sell the solid state units also. They are very reasonable.......I carry two of their modern units in every tour car to get by in the event that the original goes bad. You can just charge your battery and drive it with a bad cut out.......the ignition uses very little power. Many people on tour who have a generator go bad just charge their battery every night to get through the tour. 

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Thanks Ed. Is the universal electronic cutout from Brillman the same as a diode? I had one of those on my 34 Packard that failed and melted!

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Diodes are current rated devices, they need to be matched to the load in amperes they will be carrying.  I would suspect the maximum load your Chevy generator will put out is 20 amps or less so there should be a cutout available rated for that amount.  The universal Brill am unit Is rated at 25amps which should be fine for your car.
 

My 1937 Dodge pickup used a mechanical cutout relay and never gave me any problems in the 10 years I owned it.  The problem today might be finding replacements that are equal in quality to the original units.

Edited by TerryB (see edit history)
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4 hours ago, TexRiv_63 said:

Thanks Ed. Is the universal electronic cutout from Brillman the same as a diode? I had one of those on my 34 Packard that failed and melted!

Yes, the universal cut out electronic is a diode.......just run the regular unit.....order two, paint them both, and put one on the car......problem solved.......

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15 hours ago, Bloo said:

the most common failure of a silicon diode is a dead short, and that would have exactly the same effect, so that route never made any sense to me.

 

You are confusing consequence with likelihood. Yeah, the consequence is the same, but the likelihood of a diode failure is EXTREMELY small, thus the rationale for using a diode.

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20 minutes ago, joe_padavano said:

 

You are confusing consequence with likelihood. Yeah, the consequence is the same, but the likelihood of a diode failure is EXTREMELY small, thus the rationale for using a diode.

 
I make a living fixing pre war cars......90 percent of the generator failures I see are from diode failures causing the armature to throw solder. In the tens of thousands of miles, I have never had a cut out failure. My 32 Pierce unknown to me when I bought it, had a diode in it......and for the first time in my life, the generator cooked itself. They made millions of cars with cut outs, and they drove billions of miles........don’t modify your car. Run it stock. The diode is fine for a day’s drive during an emergency.........just run a cut out.  Simple, clean, correct, safe, and inexpensive. But what do I know........I drive twenty five times more pre war miles than the average person per year. I always recommend people take advice from people who actually have countless miles under their belt. Best to all.....Ed

Edited by edinmass (see edit history)
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38 minutes ago, Graham Man said:

I have 6 Graham/ Graham-Paige cars with stock cut out switches, the newest is 1933.  I have run all of them for over 10 years without any problems. 


 

The technology of the day worked well then, and it works well today. Why change something that was trouble free and fine when properly serviced. Nothing better than a “bone” stock car.

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  • 2 weeks later...

OK lets get up to date on my comedy of errors the last couple of weeks. I stepped away for awhile due to life, ignoring what someone said above about not leaving the cutout bypass jumper attached. I was SURE I had turned off the battery disconnect switch... but of course I had forgotten. By the time I got back the battery was discharged down to about 3 volts so I connected my battery tender to the pigtail I leave under the mat and let it go. Well, three days later the tender still showed active charging even though it read 6.3 volts. So I pulled the battery out a couple of days ago and clipped the tender on, it showed full charge after a couple of hours so I may have had a loose connection.

 

I received the parts generator a while back and checked it over, dirty on the outside but clean inside with good brushes. It has what I assume to be an original type Delco Remy cutout. I had ordered the Brillman generic cutout without paying enough attention to the photo, it will not fit this style generator due to its opposite direction mounting brackets being too far apart to attach. I will try cleaning up the Delco cutout and seeing if it works, if not back to the top...

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So I pulled the Delco cutout off the parts generator and cleaned it up, looked good, all connections solid, sanded the points lightly and sprayed it with contact cleaner. Then I removed the Niehoff cutout (which looked even better inside), cleaned up all the screws and ground areas and installed the Delco. This is the original type as the mounting holes lined up perfectly.  Started it up and the ammeter shows a charge! The needle was bouncing around a lot but it stayed at zero and showed an increase when I revved it up. First thing this morning I took it for a drive, about 4-5 miles at its comfortable 40 mph, running fine but the ammeter showed full or near full 20 amp charge all the time except when I stopped. This is with a recently tested and fully charged battery measuring 6.3 volts.

I assume this is bad news and that the cutout does not work, WTF! 

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It actually sounds like things are working correctly and it's making electricity again. Your Chevy has an unregulated electrical system, or rather, a 3rd brush regulated generator. The cut-out is not a regulator--think of it instead as a one-way valve. Current flows from the generator to the battery but when you shut off the engine, it ensures that the battery does not drive the generator like an electric motor (which is all it really is). When we first received Melanie's '56 Chrysler, the cut-out circuit in the regulator was broken and the battery was dead and the generator was cooked. Interestingly enough, the belt was also melted and glazed, because the pulley had been spinning on the trailer trip from Atlanta to Cleveland. 

 

Regardless of the cut-out, as an unregulated system it will generate a set amount of current at a certain RPM, up to a maximum (probably 20-25 amps for a car of that vintage). 


You can adjust the output of the generator by adjusting the third brush inside the generator case. The shop manual should show you how to do this. Not difficult. I have my unregulated cars running between 8 and 10 amps so it'll charge the battery but not over-charge it. If I'm on an especially long drive, I'll turn on the lights to bring it down to close to 0 on the ammeter so it doesn't cook the battery. If you don't do much night driving with the headlights on, 8-10 amps is plenty. On my '29 Cadillac, for instance, if I'm driving at night, the headlights and generator just about fight to a standstill and it shows just under 0--it'll still run for hours on battery power alone even if the generator can't keep up. If I hit the brakes or the driving light, it shows discharge, and when the overdrive was electrically operated, I actually had to turn off the headlights to engage it, then turn them back on once it was engaged. But I don't drive much at night and have replaced the taillights with LEDs. 8-10 is just about right for that car.

 

It sounds like the third brush in your generator is set to close to maximum output. Dial it back a bit and it'll still charge the battery as you drive but not peg the ammeter all the time.

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Yep, just as Matt said, the third brush is your current regulator.  It’s physical position determines the output charge current for your generator.  The cut out relay just connects / disconnects the output of the generator, think of it as an off / on switch.  The third brush should have a screw that can be loosened to change the position of it which in turn will change the current.  Take a look at your spare generator as a reference.

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TexRiv_63, As usual questions here seem to create all sorts of questionable answers and frequently go off topic. I admit I am not specifically familiar with the '34 Chev BUT I do restore antique car radios and while rebuilding a '35 Delco from Chev I was curious why there were dual contacts on the radio power switch. One set was obvious Power through Normally Open contacts to the radio supply. The other set of Normally Open contacts was fastened to ground and out of the radio? 

Long story short the Chev had a interesting design in that the 'field' terminal on the generator (that terminal next to the cutout relay with your jumper to ground) originally went to a field resister up in back of the headlight switch. That resister would be connected  to that terminal  on the generator next to the cutout relay.  When the headlight switch is turned ON (Or in the case of turning ON the radio) that resister would be shorted out and thus increase the generator output to accommodate those increased loads. 

That cutout relay is just that. It disconnects the generator when its output is less than the battery voltage so it will not run the battery down acting like a motor instead of a generator. I hope this helps.

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13 hours ago, RAH said:

TexRiv_63, As usual questions here seem to create all sorts of questionable answers and frequently go off topic. I admit I am not specifically familiar with the '34 Chev BUT I do restore antique car radios and while rebuilding a '35 Delco from Chev I was curious why there were dual contacts on the radio power switch. One set was obvious Power through Normally Open contacts to the radio supply. The other set of Normally Open contacts was fastened to ground and out of the radio? 

Long story short the Chev had a interesting design in that the 'field' terminal on the generator (that terminal next to the cutout relay with your jumper to ground) originally went to a field resister up in back of the headlight switch. That resister would be connected  to that terminal  on the generator next to the cutout relay.  When the headlight switch is turned ON (Or in the case of turning ON the radio) that resister would be shorted out and thus increase the generator output to accommodate those increased loads. 

That cutout relay is just that. It disconnects the generator when its output is less than the battery voltage so it will not run the battery down acting like a motor instead of a generator. I hope this helps.

Thanks for your response. That headlight switch resistor was an early thought in my troubleshooting process but I found out that was only used on the upscale Master models. My car is a base Standard model so the field wire is just grounded and it uses a standard early style cutout and third brush system.

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  • 3 weeks later...

To update everyone, I think my generator problem is finally solved. When I initially installed the old Delco cutout from my parts generator it worked but the charge rate was almost pegged on the ammeter. Then I had issues where the cutout did not engage at all. I removed and cleaned it again and set the points a bit closer together, after that it engaged reliably. I then followed everyone's advice and adjusted the third brush slightly and now the ammeter shows 8-10 amps when driving like it used to before all this started. Thanks for all the comments and assistance.

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