The Stovebolt Site Forums The Shop Area The Electrical Bay A little confused about my 6v to 12v set up

Since I'm hitting all the bases since I got on this forum, here's something that I need to understand, but don't yet. My '51 3100, which has a rebuilt 235, has been converted to 12v from 6v. Since I've never had one like this (the '51 I owned in the early 80's was 6v), and since I wasn't there when it was changed, I'm really lost when it comes to what is what. How do I know if the generator is 6 or 12? Same with the coil? What is difference in the schematics and parts in the system that I need to know about? I mean, since I don't even know what's what under the hood, how am I supposed to troubleshoot anything when I come to a problem? I do know that the coil has either 122/12v or 22/2v on the side of it. (Can't make out if those are 1's or not). How do I check the generator for certain? What are the changes that are made to the electrical system as a whole when the conversion is made? Probably sounds like a lot of dumb questions, but since I'm just beginning with this truck, I'd at least like to half-assed know what I'm looking at. Thanks for any wisdom anyone can lend me. Lee

If you are not sure, I would start with the generator. What is the number on the metal tag. Post it here and someone will let you know. If it is 12v than your regulator should be 12 volt too.
Your starter may be 12 volt. If it is, then the starter ring gear on your flywheel will match. 12 volt and 6 volt are different. Some keep the 6 volt starter and starter ring with a 12 volt system because it spins the starter faster, but that can run into some other problems. Check the number on the starter and post it here to find out.
The wiring harness should be the same, I belive, but all your light bulbs will be 12 volt. That may be stamped on the front of the headlights.
Your gas gauge is very sensitive to 6 volt, so there should be a voltage reducer installed that will reduce from 12 to 6. Be careful with it because it will get very hot with the key on. If you allow 12 volt to go through the gas gauge with out the reducer, will destroy it very quickly.

There may be a few more, that don't come to mind just now. Someone else will come along if I have missed anything.
Are you having any problems?

By the way, welcome to Stovebolt. LOTS of good folks here that will help you out. Just let them know when your problem is solved and what fixed it. We all want to know the end of the story.

Now that I have a little coffee in me, check your battery. 12 volt or 6volt? That may be the easiest way to tell. If it's 12 your coil will be 12 also, and there will be a ballest resistor, usually found on the firewall between the ignition switch and the coil. It probably will look like a ceramic block about 1 to 1 1/2 inches long. Follow the lead from the coil that goes back to the cab.
Man, coffee is good!
Have fun. Let us know what you find.

As with every rule there are exceptions. I'll have to respectfully disagree with this statement. There is a chance that 12v will damage your gas gauge but there's also a good chance it'll do no harm at all. In another life back in the '70s I owned a 55.1 panel truck that I converted to 12v. It never dawned on me that I might need to put a reducer on the gas gauge OR the heater motor for that fact so I didn't. I put over 100K miles on the truck after the conversion with absolutely no issues of damage to the gauge or heater motor. Was I just lucky? Maybe. I'm just saying the old mantra that your gas gauge will die if you don't put a resistor on it isn't always true. FWIW I've spoken with a few others over the years who had the same experience as me. I'm not saying that putting a resistor on your gauge isn't a good idea. I'm just saying the set-in-stone 'your gauge will die' mantra isn't necessarily fact.

If the trucks was ever driven with this electrical system, the light bulbs are the best way to determine 6v vs 12v (if you can find/read bulb markings).

Not all 12v ignition systems used the external ballast resistor. Generators, starters, and coils quite often have no markings.

Yes, a few people have reported using a 6v fuel gauge in a 12v system without using a voltage reducers. Far more people report ruining their 6v gauge (or finding a useless gauge) in their converted 12v system.

51 bolt- Just got moving, but I can say that the battery is 12v, and the coil must read 12v, and there is a ballast resistor on the firewall. I'll check the starter and generator today. Another question I forgot to mention. The coil has a green wire that's hanging off of the back (engine)side of it. Looks like it's been cut from a previous use. What would that have been for??

Maybe a tach. Someone will know

tiny and tclederman- Thanks for that advice, and I'll check that, too. I appreciate any kind of heads up at all, since this conversion deal is all new to me. I've always worked on my own vehicles, except for "deep" engine stuff, like rebuilds. But, as I said at first, when you look under the hood at a system that's been re-done, and you aren't familiar with the particulars, I don't know WHAT I'm looking for (or at). So, with your help, I'll map out what is and isn't ok for this truck. I will say that an experienced rebuilder of old vehicles did the change for the guy I bought it from. I think it's all done right, but since I don't know right from wrong on this type of change, I don't know what to look for. Thanks again!

If you have a foot-actuated starter, the switch on the starter-body might have a side-post on it. A lead/wire from that post would go the "input" side of the coil. There would also be a lead/wire from the ignition switch, through the ballast resistor, to the "input" side of the coil.

Also I should clarify, I'm not saying to NOT put a resistor on your gas gauge. It would be prudent to do so. My issue is with the doomsday scenario that you will 'always' fry your gauge when that simply isn't the case.

Yep, I have a foot starter. Was going to say there's a wire going from it to the resistor, but I'd better check to make sure, because it seems like the wire to the resistor is coming out of the wire braid from the dash, with a wire leading to the resistor, then to the coil after that. Like I said, let me check. I looked at a lot of wires yesterday.

What would happen if the ring gear on the flywheel wasn't changed to match the 12 volt starter?

Dusty, if you have mismatched gears, things don't work ... and one or both of the gears get chewed up

Bill

The diameter of the flywheel changed when Chevy went to 12 Volt. Why? I have no idea. When they changed the diameter they changed the tooth count and the pitch. On the starter they changed the pitch of the teeth, and kept the tooth count the same. Why? I still don't know. So in short, if you have a 6 Volt flywheel, you need a 6 volt starter. It will work just fine with a 12 Volt system. If you have a 12 Volt flywheel, you need a 12 Volt starter. It will not work with a 6 Volt system. But there is some good news, they will interchange, and fit on 216 and 235 engines. They will fit inside the old and new bell housings. So if you have an AD truck and you put in a later 235 use the old bell housing and flywheel and you are good to go. The bell housing was changed on the TF trucks. I think that was to fit the new at the time V8. The cross member was changed for the same reason. Since the TF were 12 Volt it was simple I think to make the diameter the same as the fly wheel as the V8 and save messing around with different starters? Best I got any way. By the way, the ring gear is specific to the flywheel. You need the small diameter ring on the small diameter flywheel. Any one find an error in this?

Steve and Red, Thanks - I think I'd better be checking what starter I got because the 54' was converted to 12 volt and when I was under it over the weekend I noticed that the ring gear looks a little gnarly at the beginning of the teeth. It starts fine with no noticable noise. Is there a quick way to tell if I got the right combo? When I get back home Friday I'll see if there is a tag on the starter and start researching.

converting to 12V doesn't require changing the starter .... ring gear teeth can get a bit gnarly with age, but if mismatched I don't think it'd crank .... if it still has a tag on it, black= 6V, red= 12V .... otherwise you need to count the teeth on the flywheel, altho I forget the numbers right off [someone will chime in]

Bill

Hy Steve_H and guys, the engine rear crossmember design and bellhousing mounts were changed in 1954, I have no idea why the design was changed as the advent of the V8 and the next generation of truck design turned out to be eighteen months away, I just wanted to clarify when the crossmember design changed, hope that helps, now lets get back closer to the original subject of this post.

Changed the cross member to accommodate the hydramatic which was
introduced as an option in '54. The angled saddle style mounts
gave better support than the earlier horizontal cantilevered
mounts. You have to remember that future designs were on the
drawing board and evolving many years before they were
implemented. The '54-'55 AD is a good example of that process.
dg

Maybe it should be noted, in addition to Denny's comments, that the new-design 1954 rear-engine cross-member allowed 3 and 4 speed transmissions to be mounted without a rear-of-transmission mount, eliminating the the frame cross member for a rear-of-transmission support with either manual transmissions.

The new (Chevrolet truck) Hydra-Matic was introduced in 1954, and it required a rear-of-transmission mount on a removable frame cross member (only used with Hydra-Matic transmissions).

GMC had a domestic truck Hydra-Matic transmission in 1952 on one model, and a H-M transmission option on all light/medium trucks in 1953 - both years/transmissions using the old style rear-engine cross-member (and, of course, a rear-of-transmission mount and cross-member).

Dumb question, but, what do AD and TF stand for?

Abbreviations of Chevrolet truck series names

Chevrolet Advance-Design 1947-1955 (GMC New Design series/years)
Chevrolet Task Force 1955-1959 (GMC Blue Chip series/years)

Thanks. Didn't know that.