VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 39 light duty stalling

Greetings - recently received a 1939 light duty from my Dad. The truck was bought brand new by my great grandfather in '39. Dad had it since '68. It has been fun to learn and tinker with the truck. It is essentially in it's original configuration (6 Volts, 216 enginer) with a rebuild and a few add-ons (blinkers, running lights, a second break light).

I have been playing with the brake lights and blinkers a bit, Dad never had them 100% functional, and i plan to drive it a bit more than he did. I did not rewire anything, but checked all the bulbs, traced wires, etc. He did add on an LED brake light bar in the rear window years ago.

That all said, I have had a few instances when the engine would stall when the brake pedal was applied. It will do this standing still. I have not driven it that much. It stalled last night twice, once just bringing the truck into the garage from the driveway. I restarted her, and pressed the pedal again, and she stalled again.

My initial thoughts are there is a short somewhere, or that the brake lights are draining the electrical system enough to stall the vehicle. The battery seems to be holding a charge (6.15V to 6.2V, over 7V when running so the generator seems to be ok).

Any thoughts or suggestions or similar experiences? Thanks! I am enjoying this forum as I learn about the truck.

Start with the simple stuff. Your brake lines feed a switch under the floorboard somewhere. Probably attached to the frame around the middle of the truck. It should have two wires connected to it, one is 6v, the other should have no volts until you press the brake. If you disconnect the No-volts side, that will remove the brake lights from the circuit. If the problem goes away, you know the short (wire touching ground) is from that switch back. If it doesn't go away then the problem is most likely in the switch itself. And I'm not sure I've ever seen a switch like that short voltage to ground but it's old. Stranger things have happened.

Wow!
Beautiful truck!

Welcome to the site, you've found the best place for lovers of stock Chevrolets.

I've seen light wires etc short or ground to the point of burning the wire off before, but never seen it kill the engine in the process.
You've got something really unusual going on.
I'd start by tracing the wiring supplying the ignition circuit all the way from the starter post to the coil, and look for things peripherally connected that shouldn't be there, or things the circuit is running or bypassed through that it shouldn't be.

Good luck 🙂

PS
How does the ammeter react when you apply the brake and this happens?

I had an issue with my 41 where it would die occasionally when slowing down to a stop. Or at ide it would die intermittently. I was lost attempting to figure it out. Only occurred after driving and when slowed down or at idle. It died when there was any extra draw on the system, not just the tail lights. Turning on the headlights would increase the likelihood of it happening. Strange as it sounds changing the coil fixed everything. Not only that the car started better and appeared to have more power after that point. Apparently it was on its way out since I got it running. Since I had never had a good one I did not know the difference.

NAPA had one in stock for under $20. Might be worth a try. If your spark is weak already the extra draw could be just enough.

Thanks for the inputs so far. It is a beauty. Dad did a great job.

The issue is intermittent as well, which doesnt help.

I will check the ammeter next time I start her up/see the issue again. Will also check the hydraulic switch, and will be ready to shed some load as we say in the aero business by removing break light bulbs if I can get the stalling to repeat itself.

This might be heading things in the wrong direction. I wonder if the fuel level in the float bowl is to low. When you brake the fuel sloshes forward and away from the passage the feeds the idle circuit.

Just an idea.

Does the stall happen when you brake very lightly? Or only under normal and heavy braking?

If it happens under any braking then I agree that there might be an electrical drain.

Or is the throttle linkage so worn that it lets the throttle plate close too much? Also check the wear of the throttle shaft in the throttle body portion of the carburetor.

That leads me away from anything fuel related. It almost has to be electrical. If you had a dead short you would let the smoke out and you don't mention that happening. Try revving it up to get full charge out of the generator and step on the brake pedal. I'm kind of leaning toward Monty's hypothesis of a weak coil and the extra draw of the brake lights being the straw that breaks the coil's back. Automotive electrical gremlins make my head hurt.

Rusty - It happens (sometimes) when sitting still and when braking lightly..

Just a thought. If it’s an extra draw issue affecting a weak coil, then the same thing should happen by turning on any other load such as headlights, horn, heater, etc. If it only happens when the brake lights are activated, then I would assume the coil is good and the issue is associated with the brake light circuit. By chance has the light duty been retrofitted with a signal light switch that uses the brake light filaments? Mike

Thanks for that clarification.

I agree that a quick check is to simply pull one of the wires off of the brake light switch.

. I had a 39 half ton PU with similar problem. When I stepped on the brakes, the engine would die. I immediately suspected a shorting stop light switch so disconnected and tested the wire to brake light. It also stalled when descending a hill in gear. .
.Finally I stopped using the emergency brake and it stalled. Some how the carburetor was the cause. A $5 rebuilt carb from Grand Auto cured the problem. I never understood why this happened but a few years later it happened again on a 37 chopped sedan. Both happened over 50 years ago. I may still have one of the carbs that I didn't turn in for a core. .
. Lou .

If your truck has its correct original electrolock ignition switch/cable in place, a coil from the parts store can be made to work but will not be an instant swap-in. If you have car buddies with 6 volt stuff, maybe you could borrow a coil that is known to be good. Use it for testing purposes and then search for an original type coil if needed.
What is your Dads first name. I might know the truck.

Mike

Dad is JJ/Jim. Another symptom: after it stalls, I can not immediately get power back on to the gages. I know power is getting across the ignition switch to the leads going to the dash although I haven't checked power at the coil. If power is not getting to the coil will that cause the gages to not work?

Thanks again.

I've found that when dealing with something this old and it seemingly has sat for awhile, AND having these types of symptoms... if you can, you may want to disconnect as many things as possible from the system. As in, if I'm not mistaken there is one main wire that feeds pretty much everything under the dash to include the ign. Switch, the gauges and almost everything else. If you've disconnected the brake wire at the frame there shouldn't be much else in the system. Hotwire from the battery to the coil and then to the starter relay. Leave the coil wire attached and remove power from the starter once it starts. If this solves your initial problem then reattach as few things as possible one at a time until the problem comes back.

Another approach is maybe try crawling over and under everything that has a wire connected to it. If the problem is intermittent then most likely something is loose or has a faulty connection. Pull on connections. If it falls apart in you hand then it was either already bad or going bad. Fix anything you find. You'll be surprised how well that works. Not everyone understands electronics but anyone can recognize a broken or loose wire. Look for anything that is corroded. You may just have a bad connection on the battery or ignition switch. More problems are found by just a good visual and touch. Most of us overthink our problems. As they say "It ain't rocket science".

Hi CT2TX

As originally wired, '39 trucks fed only 2 things through the ignition switch.
The ignition circuit (to the coil)... and the fuel gauge (the only electric gauge on the instrument panel).

So...
That suggests you have a bad ignition switch that loses it's connection, and then you have trouble getting it to make contact again.

But that leaves the question...
How are your brakes tied into this?

PS
Has the lead to your brake lights etc been improperly attached to the ignition switch instead of the ammeter?
If so, the additional load of the brake lights may break the poor connection in the ignition switch and kill the engine.

This would mean you may have 2 coexisting problems.
The wire to the lights etc attached to the ignition switch.
And an ignition switch that has been overloaded and now doesn't make proper contact.

If you still have the original Electrolok I vote for a bare wire shorting out inside the electrlok cable shield.

The reason it stalls is that just before you apply the brake you let off the gas. So the engine moves in the mounts. That movement then moves the cable shield so the bare wire shorts to ground. .

Guys (and maybe girls) we can speculate this problem until the cows come home but sooner or later CT you're going to have to do some good old fashion troubleshooting. We've given you all the information you should need to figure this out. You gave us voltage readings earlier so it would appear you know how to operate a volt meter. Isolate the things out that you know it ISN'T. Then deduce down what's left until you find it. As it stand right now all you're doing is Rabbit Hunting and dragging us down the hole with you. Come on, you're in Texas. There's gotta be some horns you can grab onto.

CT2TX,
Yours is not the truck I knew about. I wish I had something to add to help with your problem. If it goes the way it usually does with me, you will find something simple and obvious, when you get into it.
Best of luck.

Mike

Thanks for all the inputs, I built a new ignition switch over the weekend - will install it once it warms up here in TX (unheated garage). Then move on to the coil if that does not address the issue. I will follow up then.

So let's hear it. What was the fix?