1964 C30 Towing Capacity

I have a 1964 C30 Dually completing a full restoration, replacing the 230 - I6 and 7200 lb rear H072 axle 5.14 gears, with a remanufactured 350 cid with Max Flow EFI-500 fuel injection, remanufactured 1980 14 bolt 8000lb rear dually axle with 3.73 gears, added double reservoir power brakes. All drum brake hardware rebuilt or replaced with new. New remanufactured SM420 with Novak front seal upgrade and added synchronizer between 1st and 2nd gear, final gear ratio 1.0. I am looking to tow a 5th wheel in the 5000-8000 max range. I won't be towing often, a couple of times a year between Virginia to Tennessee. GVWR on the truck plate is 10k. The trailer will have brakes. I won't be adding disc brakes, and surely looking way ahead with the setup while towing.

Let me know your thoughts on if this is doable with enough margin for a 5000-8000 fifth wheel RV.
Thanks

[roll_the_dice]

I don't know the answer, but would love to see the truck! I am about to start a 1964 GMC 1 ton dually build and am looking for inspiration...

[justa dumb hick]

My only thoughts are: sway bars and shocks.
If you’re over 50, then you already understand the limitations of drum brakes, and I’m guess the C30’s have big ones.
I’m also assuming the rear springs have been selected to match the trailer load? I don’t see why it wouldn’t work. You may have a few teething problems to resolve initially, but these old trucks were built and designed to work hard...which they did uncomplainingly for many years. Keep us in the loop and let us know how it works out.

Originally Posted by justa dumb hick

My only thoughts are: sway bars and shocks.
If you’re over 50, then you already understand the limitations of drum brakes, and I’m guess the C30’s have big ones.
I’m also assuming the rear springs have been selected to match the trailer load? I don’t see why it wouldn’t work. You may have a few teething problems to resolve initially, but these old trucks were built and designed to work hard...which they did uncomplainingly for many years. Keep us in the loop and let us know how it works out.

Yes, I'm an old dude. I think the 10000 GVWR is conservative for this beast.
Thanks

[Captainfab]

My main concern would be if you have any sizeable hills or mountains to go over. The 4 wheel drum brakes may or may not be up to the task. As far as the rest of your truck, I see absolutely no problem with towing a 8000# 5th wheel.

[Chuck73080]

Actually, IMHO a mixture of disc and drum brakes are a hindrance rather than an improvement. Drum and disc brakes need different techniques under compression braking. Disc brakes require an on/off technique to allow the rotors to cool, while drum brakes do best with a continuous light application without modulation. With drums keeping the brakes applied doesn't allow oxygen between the drum and lining to promote a brake fire.

The most important thing to remember is to make sure your brakes stay properly adjusted. Don't be afraid to use you engine compression to help brake and a good rule of thumb is that you want to go down a hill one gear lower than you went up and that may be too fast. Also at the first hint of brake smoke don't hesitate to stop, then put your trans in granny gear, set your parking brake (driveline) kill the engine and let the clutch out to hold the truck. It may take 30 to 60 minutes to cool your brakes, but it's a lot better than a runaway.

A word of caution, I've done this in diesel trucks many times before Jacobs Brakes were fully adopted, however gas engines have much lower compression and may not hold, depending on the grade. If you have to use your foot brake while they cool, it could cause your drums to warp.

[Chuck73080]

Originally Posted by LenDill

I have a 1964 C30 Dually completing a full restoration, replacing the 230 - I6 and 7200 lb rear H072 axle 5.14 gears, with a remanufactured 350 cid with Max Flow EFI-500 fuel injection, remanufactured 1980 14 bolt 8000lb rear dually axle with 3.73 gears, added double reservoir power brakes. All drum brake hardware rebuilt or replaced with new. New remanufactured SM420 with Novak front seal upgrade and added synchronizer between 1st and 2nd gear, final gear ratio 1.0. I am looking to tow a 5th wheel in the 5000-8000 max range. I won't be towing often, a couple of times a year between Virginia to Tennessee. GVWR on the truck plate is 10k. The trailer will have brakes. I won't be adding disc brakes, and surely looking way ahead with the setup while towing.

Let me know your thoughts on if this is doable with enough margin for a 5000-8000 fifth wheel RV.
Thanks

Would you mind sharing your source for the 14 bolt?

I'm going to swap my rear also, although I want a 3.56 (my tires are 225X75R16, 29.3" Dia.} for 2388 RPM@75 MPH with Gear Vender OD, 3062 RPM without. My 396" SBC crate engine dynos at 460 ft lbs @2400.

Here's a link to a Spicer RPM calculator.

https://spicerparts.com/calculators/...rpm-calculator

The first gear syncronizer in the SM420 sounds good, mine only has 62,000 miles but it'll be out anyway so it may be worth an exam, and synchronizer addition.

Please let us know if you have pictures posted of your truck because I would love to see it.

Chuck73080

Originally Posted by Chuck73080

Would you mind sharing your source for the 14 bolt?

I'm going to swap my rear also, although I want a 3.56 (my tires are 225X75R16, 29.3" Dia.} for 2388 RPM@75 MPH with Gear Vender OD, 3062 RPM without. My 396" SBC crate engine dynos at 460 ft lbs @2400.

Here's a link to a Spicer RPM calculator.

https://spicerparts.com/calculators/...rpm-calculator

The first gear syncronizer in the SM420 sounds good, mine only has 62,000 miles but it'll be out anyway so it may be worth an exam, and synchronizer addition.

Please let us know if you have pictures posted of your truck because I would love to see it.

Chuck73080

My source contact is mailto:scott@ausedparts.com

[62c30]

I have a 62 c30 that I have swapped in a 14 bolt out of an 81 c30. I tow with it frequently a bumper pull trailer weighting 4-8k. It handles the weight just fine and would easily pull more except the brakes suck. I have a brake controller on it and am very observant of my surroundings while towing. I am getting ready to swap the front out for the front out of the 81 for the brakes. I might end up swapping in a 12v cummins after that.

[Chuck73080]

Originally Posted by LenDill

My source contact is mailto:scott@ausedparts.com

Thanks for the info.

Chuck

[leadsledray]

at least with the 1st gear syncro you'll be able to downshift when the drum brakes fail!

seriously though, braking is as much a part of towing capacity as anything else. i would seriously consider an upgrade to 4 wheel discs, and my preference(optional) for a working truck: hydroboost. this can all be done fairly cheap and easy.

[vince1]

I think you'll be OK if you drive sensibly and all the brakes are working as they should. We used to have a 67 1 ton with duals and I don't remember braking being a problem.

If you were to spend a lot of time driving in the city then maybe PS would make the job easier. On the highway manual would be easier.

[66x3]

I tow a small camper trailer, a 16 ft car /equipment trailer or sometimes carry a Approx. 2000# slide in camper with my C 20 and seem to do fine with my drums. They are pretty big brakes and truck/tractors have used drums for decades although just recently started using discs. Maybe Studeclunker should weigh in on this as he seems to tow some pretty big vintage trailers but I don't know if he has switched to discs or still has drums. I for sure switched over to a dual master cylinder.

[Chuck73080]

opps