Towing capability

[jrmunn]

A few other thoughts. My 64 1500 was originally equipped for a camper. It came with oversized front drums and vacuum assist brakes. The vacuum assist was removed after taking the camper off because the drums locked up too easy with no load. But even when new, the need for brake assist was recognized. And, assuming you have a standard transmission, how good is the clutch. The truck plus 14,000 pounds is a lot to ask from the stock clutch. The stock SM 420 transmission with compound low is probably up to the job, and you might already have a heavy duty (8 lug) full floating rear axle plus 4.10 rear end in a 1500. Also to be considered when stopping are the trailer brakes. If they can't slow the trailer down, then you will have a potential jackknifing problem - especially if the road gets slick. And thinking of some of the grades in Colorado, you might even need a fire extinguisher for the brakes. Sorry, but there are good reasons that today's big trailers are usually pulled by more modern 3/4 and 1 ton pickups with large engines, exhaust braking, and big disc brakes. I know because I pull a mid-sized 5th wheel (at about 14,000 lbs) with a Dodge 2500 that has a 6.7 liter Cummins diesel engine. It would probably pull a house, but I still have to let traffic by on steep uphill grades. And despite 4-wheel disc brakes and good trailer brakes, I am grateful for the engine brake when going downhill. The old GMC is a family keepsake and, with the bed lower to the ground, is great for loading. But I would not pull a big load with it and, honestly, I would hate being behind you going uphill or having you coming downhill toward me while pulling such a heavy load.

JRMunn

[Ed Snyder]

Originally Posted by Arubariba

With "1500" that means you have a C10 that is a 1/2 ton pickup truck?

You're confusing '60 to '66 model numbers with '67 and later model numbers. A half ton GMC from '60 to '66 is a model 1000. A three quarter ton is a 1500. A one ton is a 2500. Starting in '67 a half ton GMC is a 1500, three quarter ton a 2500, etc. "C10" is strictly a Chevy model number.

[bigblockv6]

Originally Posted by Arubariba

With "1500" that means you have a C10 that is a 1/2 ton pickup truck? It won't handle 14k. I have a 1972 C20 (3/4 ton) that I converted to a C30 (1 ton) with a 4:10 dually rear end, big brakes off a 1989 1 ton truck (front disks, rear drums), vacuum booster, 5k rear air bags, trailer brakes, LS1 engine, 5 spd NV4500, digital dash, ETC (make that a LONG ETC!), lol. I have pulled 14-15k with the truck and I've had 8k on the steel flat bed and I would not recommend anyone doing that with similar setup as mine, much less on a 305 1/2 ton truck. Even with my big brakes, brakes are still the weak point.

Arubariba, 1500 applies to 67 and up half ton trucks, prior to that 1960-66 3/4 ton GMC trucks were 1500 series, 1/2 tons were 1000 series and 1 tons were 2500 series

[Gimmie1965]

Thanks JRMUNN,
yes it does have the 4:10 full floating axle. The clutch has been changed. In traffic I have to put it in nuetral or else my leg gets to shaking so bad that I'm not able to shift at all. I have 5000lb airbags that I'm installing this weekend along with a new floor for the bed. Planning to make it a dually with 4 wheel power disc. My main concern is if the 305 will be able to pull it. I'm not concerned about speed. Looking at doing the 351m head,intake,exhaust swap in hopes that will help with pulling. It will be a 5th wheel setup at least that's the plan. Found a 82 gmc standard cab dually with a 6.2 diesel. Was really excited about it but after long thought I decided against it on the fact that it wouldn't be same truck.

[Arubariba]

Originally Posted by bigblockv6

Arubariba, 1500 applies to 67 and up half ton trucks, prior to that 1960-66 3/4 ton GMC trucks were 1500 series, 1/2 tons were 1000 series and 1 tons were 2500 series

LOL, Living and Learning,:rowdybe er:

[Clarke]

Other than the aluminum radiator, clutch fan, taller tires and single into dual Flowmaster 10, mine is original. I did replace my 4:56 with 4:10, so I could do 65 mph. I tow our 4K lb camper all the time in the flatlands and able to maintain 60-65 mph unless a long hill. The early GMC 1500 is a 3/4 ton and is rated for 5K lb tow capacity.

I have towed 7K lb several times in the flatlands and in the Ozarks. In the Ozarks it’s not pretty... I can get up to 55-60 mph without too much trouble when it’s flat, but end up down shifting several times before I hit the top of the hills, doing 10-25 mph in a 55 mph zone. Not fair for other drivers, but I only do it when I rent skid steers and haul gravel.

I’ve never had any trouble stopping, since I installed an electric brake controller and make sure the trailers I tow either have electric or hydraulic surge brakes.

I couldn’t imagine towing 14K lb out on the road with the way our trucks are set up. As others have mentioned, you need a larger motor with additional torque and horsepower. Plus, there’s not enough gears in our transmission. 3rd and 4th gears are worthless for towing heavy on grades. If you’re idleing around on the property or dirt roads, granny low has a lot of guts. But if you don’t have enough tongue weight, you’ll lose traction. I have a set of off-road chains to put on sometimes when towing heavy on grades and breaking traction.

[jrmunn]

At this point, you are out of my league with improvements. But about your main question, my experience has been that the 305 is underpowered for even loads in the bed. In my case, top speed in third gear is about 35 mph, and second is about 20 mph. Clark is right about trailer brakes, gears, and a bigger motor. Having lost all hydraulic braking when a front hose broke, I would strongly recommend a dual master cylinder system (which I have now). And I put a Holley 4412 (?) carburetor on my 305. It helps, but not enough for your situation. I am also not sure you could use 351 heads on a 305, but others probably know for sure. If they fit, magnum heads plus intake and exhaust manifolds would also help. But then you might have trouble finding enough gas stations. On paved roads with a 5th wheel setup, you are probably okay with traction, but be aware that the stock rear end is single wheel drive (not positraction). I would also worry about tire and wheel capacity, where your idea about dual wheels would help a lot. Finally (for me) there is a question of what happens if a patrolman wants to see if your setup meets legal requirements. This is uncharted territory for me. Good luck with your decisions and travels.

JRMunn

[bigblockv6]

[QUOTE=Gimmie1965;69267]Thanks JRMUNN,
Planning to make it a dually with 4 wheel power disc. My main concern is if the 305 will be able to pull it. I'm not concerned about speed. Looking at doing the 351m head,intake,exhaust swap in hopes that will help with pulling.

The 351M head, intake, exhaust swap won't do quite well with the 305, JR Munn was quite correct with that statement. This type of conversion will actually lower the compression ratio on the 305. You will be much better off like I mentioned before with a larger displacement V6 and a 401M that you think is too big is actually optimum for the amount of weight you intend to pull. Even if you come across a 351M that will be a significant improvement over the 305. As far as a dually conversion the 305 can handle that, for a while back in the 60's my father actually ran dual rear wheels on his 62 1/2 half ton with the 305D V6 and 3.54 gear ratio. Myself I yanked out the 305E out of my 68 K2500 and replaced it with a 478M V6 there is no substitute for cubic inches. The bigger V6 will still for the most retain the appearance of your 305.

[jbgroby]

I'm buying a canner ham trailer with a weight of 2700lbs. I too was wondering if I needed to change my brakes up front?

[FetchMeAPepsi]

Originally Posted by jbgroby

I'm buying a canner ham trailer with a weight of 2700lbs. I too was wondering if I needed to change my brakes up front?

I've towed 3400 lbs with Cecilia with no problems other than allowing more room to stop of course, but not much more than I'd do with any other truck. I think you'll be fine there.