The Stovebolt Site Forums The Parking Lot Big Bolts 6 or 12 Volt...630 Series

Haven't had much time to work on this former fire truck yet. Got it delivered, put a 12 volt battery in it along with a temporary fuel can and backed it 100 yards up my driveway and into my storage building.

Previous owner claimed it required 2, twelve volt batteries to start. The manual says it could be either 12 or 6 volt positive ground, of course I didn't know it was supposed to be pos. ground and hooked it up neg ground.

What is the best way to tell which way is correct? Hope I didn't screw anything up.

Hy Verdigris, please remember to tell us the year of the truck you are making inquiries about. GMCs were positive ground up into the sixties, If your truck has an alternator rather than a generator it may have damaged some diodes, some alternators had an isolation diode at the output, if that is the case with your alternator then no damage would have happened. If you check the colour of the tags on your starter and generator if your truck still has one that should tell you the voltage. red tags are for twelve volt equipment, black tags are for six volt equipment. Your coil may also be marked for voltage, the primary coil circuit should have the positive post of the coil going to the distributor if the truck is positive ground, hope that helps.

Also what engine? I suspect the Diesel was 12V

Sorry, I should know better.

Truck is a 1954 630 series, 503ci engine. Pretty sure it has a generator, I'll check for tags tomorrow and also check the coil wiring. Thank you both for responding.

Just out of curiosity, how tough would it be to swap out the 503 for a 471 or 453 detroit? I know that 471's were an option in those series but I don't know if the frames were the same in the diesel trucks or anything else was different. And yes, I know detroits are noisey , underpowered oil slinging boat anchors. That's what I like about them!

GMC was still using 6v positive ground in its big trucks (all trucks) in New Design 1954/55st (Z-series GMC).

Blue Chip 1956 GMCs were 12v.

Late 1955 GMCs (Blue Chip) had 6v or 12v (big trucks were most likely 12v).

Two, probably 12 V batteries were in there, that is what is in my '54 630 with a 503. If a giant alternator, must change diodes on housing to use neg. ground system. Put in a 4.33 two speed, helps with the speed. Had to install a later model GMC water t'stat. Got juice brakes working, too. Removed 16' bed, shortened frame 4' , going to 8' bed.

If the brakes don't work, a .375 Allen wrench rotated in wheel direction will tighten them, however, the mechanism is zink, most likely, easily broken, so don't lean on the wrench too hard. Repair is difficult.

Changing to a 4-71 could be done, some cowling work, radiator shutters, air intake and filter, etc. Might be an overwhelming project. A Cummins 6-bt would fit right in there, but it wouldn't sound right.

Ed.

Hi Ed

I was hoping you'd chime in, since our trucks are identical.

So it probably came with two 12 volt batteries and positive ground.

I would love to see pictures of your truck sometime as it sounds very similar to what my plan is: shorten the frame and the fire body and install a two-speed rear.

The Detroit thing is only if the 503 turnes out to be junk. Thanks once again for the info, I hope to be getting into the brakes in the next couple of months.

Tclederman, I wonder if, since they were fire trucks, they were outfitted differently

Unless you're planning to operate all the fire truck electrical equipment continuously, all you need is one good-sized 12 volt battery. That's how I drove Ed's truck from Tennessee to the KC reunion a few years ago. If it's got the Leece-Neville alternator on it, the polarity can be swapped to negative ground by just swapping a few wires around- - - -no need to change diodes. The big DC generator that was probably original equipment and the huge DC voltage regulator is a whole different can of worms! I've got the Delco-Remy service bulletins for those items stashed away somewhere.
Jerry

Jerry,

Thanks for chiming in, I removed the second battery since the second was dead anyway.
One is plenty, the starter is geared, so no giant current draw.

The 503 is a good engine, milled the head .090" after measuring that was OK. Most of the cyl. head bolts were loose on mine, so no chance of repair without new head gasket (rare).

Had to have new intake valve guides made, since found some on EBay. Since you live in the rust belt, worse than MO where my truck was, plan doing the brakes. Is there a bed on your truck? Let me know when you are starting on the brakes.

I'll send you a px of my shortening if you send me your email?

Ed

Hmmmmm- - - - -that's interesting. I torqued the head 3 or 4 times while doing the water glass treatment to temporarily seal the leaky head gasket. Maybe it was in the process of deteriorating due to old age?
Jerry

Jerry, I think the addition of anti-freeze is what failed the water glass, it did fine until I added the antifreeze.

Ed

Yep, that was an old-school trick from back when most antifreeze contained alcohol, not Ethylene Glycol. The upside was that the water glass got the truck home without a big towing bill. That was a fun trip, and the 1500 miles on the motorcycle through 4 states on the way home put the icing on the cake!
Jerry

Thanks for the help everyone.

I'll try to have my wife post some pictures of the truck tomorrow. Yes, it still has the fire apparatus on it.

Ed, my email is searle1959atgmail.com. Just change "at" to @. Looking foreward to pictures!

The generator is a deco-remy, says twelve volt after I cleaned it off. The regulator is a "Blue Streak" Polamatic, also a 12 volt with 3settings.

Would I be better off getting a one wire alternator and a different voltage regulator?

What are my choices for two speed axles that will be compatible with my truck. I plan on getting rid of the pump so a custom drive shaft will have to be made.

Thanks again.

Verd

Choices depend on availability. Most shops won't know what an 1890 rear end is, since it was a made for GM only. You will have to find a grey haired trans and diff. guy who knows what you are talking about. Another option would be to put a Brownie in there. 6241 was a factory option. Would fit in place of your pump.

I will give you the phone number of the old time gentleman in Duluth I got my 4.33 two speed from when I find it.

When you get around to doing the rear brakes, the sooner the better, cups and covers are available new, no other brake parts are available. The shoes are rare, perhaps made of zink, looks like Al, everyone wants them, no one has any. To remove the Dayton wheel/brake drum assembly without having to remove it to the ground-they are heavy-use two inexpensive cable come-along. Wrap one cable around the end of the hub, where the axle attaches, and keep it there, wrap the other one around the drum as far as possible inboard to help pull the assembly off. Never have to lower it to the ground, bearings and seal are removeable from there. After you have checked the bearing tightness WITHOUT the seals, install the seals, then move the inner come along outboard and hook the top to the top of the inner frame railto help pull the assembly together. This is assuming both comealongs can be attached to the bed rail, on the outside of the bed. Be careful when ordering new seals, mine were CR, which crosses over to SK directly. I have the number somewhere if you cannot find it. Other seals, FM, for example, have a smaller piece OD steel that will not fit over the hub properly, even though they cross over to the CR number.

I'll send px when all put together, waiting on nuts now.

Ed

Would a brownie give me the higher cruising speed? Sounds easier than swapping an entire rear end. I've driven trucks with 2sp. Rears and also 5&3's and 5&4's so either is fine with me. I can't imagine I couldn't find an old brownie locally. Lots of old rusted out trucks around here.

Thanks once more.

Verd

Once you get the hang of using two shifters, a Brownie gives you a lot of options. Each main box gear will have three ratios to choose from, under/direct/over and the top gear overdrive position will give you a better top end speed. I'm planning to do exactly that with a 1961 American LaFrance pumper I've got stashed away out in the pasture, with a 401 GMC V6 and a driveline mounted fire pump. I got my Brownie in a horsetrade with another bolter down in Louisiana, so all I'll need to do is acquire some shift linkage. I'm also planning to discard the fire bed and install a commercial 5th. wheel and a gooseneck trailer hitch. Presently, the truck has a Clark 5 speed, but 5th. gear is direct drive, not OD.

Back to the original question about voltage and polarity- - - - -As much as I like to tinker with old-school DC generators and regulators, a 12 volt negative ground internally-regulated alternator somewhere in the 100-120 amp range will handle any reasonable electrical demand you're likely to encounter, including running the fire apparatus equipment in a parade, etc. One big 12V battery like a Group 30 should be all that's required, battery-wise. A General Motors 12-SI alternator from a big Oldsmobile or Cadillac from the 1990's should fill the bill nicely, and all that's really needed to swap ground polarity is to reverse the primary wires at the coil and swap battery cable connections, obviously. Everything else- - - -starter, heater blower, lights, etc. should operate OK on either polarity. The gas gauge might require a little tinkering to read correctly on a negative ground system. Good luck!
Jerry

Sounds like I have the same firetruck too. Mine is a 54 630 with the 503 but mine came with two 6-volt batteries and negative ground. Is this therefor 6-volt everywhere? (lights,etc) or 12-volt. I have a new 12-volt 0ne wire alternator installed but haven't connected the wiring yet as I'm not sure how to hook it up. Thanks, Ron.
Also mine has the disc break e-brake setup. Does all three of yours? I want to get rid of the fire apparatus too, but what do you do to hold the e-brake in place cause the disc is mounted to the fire pump?

The two 6 volt batteries are wired in series to provide 12 volts, like the old British cars such as the MGA do. Somebody probably swapped the ground sometime in the past, as almost all GMC's of that vintage left the factory as + ground. Move the E-brake to the back of the main transmission- - - -brackets should be available to do that or you can fabricate your own. Ed Pruss can probably provide some information on that brake system if you send him a PM.
Jerry

Thanks for that info. So when I hook up my alternator are my gauges going to work properly?

If I was there to wire it- - - -yes. There's no substitute for 50+ years of experience at this stuff, and that's something the very best advice on the internet can't accomplish. Find a good automotive electrical guy and pay him handsomely for his knowledge. Or- - - - -do it wrong and breathe a bunch of very expensive smoke!
Jerry

I was able to find a 4.33 two speed diff. That fit right into my 1890 rear housing(1890's) are GM only so hard to find in books. Look up on old time repair shop, some of the old guys can figure it out.

A Brownie with a Tru-stop brake mounted would be a good alternative. A 6xxx series Brownie with a 10" or 12" brake would work fine for a hobby truck.

Ed

CFF,

I just took a px of my Tru-stop brake. Px does not show mounting details. All the brake assembly bolts to the trans with bolts above CL of trans and above speedo take off, so if yours attaches to pump with those bolts, you might be lucky. On my trans, there are no other possible mounting bolt holes below the CL that might be used.

Regards Brownie vs. two speed mounting differences: I have done both, two speed axle shafts are equal length, one speed are different lengths. Make sure to get equal length axles w/ two speed. I did mine outside on gravel driveway over Labor Day weekend one year. With Brownie, making and attaching crossmember(possible upside down welding) possible making companion flange ends on driveshafts, making brackets and hooking up shift rods, etc. I vote for two speed being easier. Of course if replacing pump, it gets more complicated.

Ed

With accurate measurements and some basic metal fabricating and welding skills, those Brownie mounting crossmembers can be built on the workbench and all that's needed to be done on the truck is drilling a few bolt holes in the frame - - - - -the vertical part, NOT THE FLANGES! Then give a driveshaft fabricator some accurate length measurements and let him figure out how to build and balance both shafts. Dana/Spicer has an excellent tutorial on setting up multi-piece driveshafts, and I believe it's available on a website somewhere.
Jerry

Links for the Spicer driveline setup manuals
https://www.stovebolt.com/techtips/driveline/setup/index.html