The Stovebolt Site Forums The Shop Area General Truck Talk Questions about 3/4 ton vs 1/2 ton and the pontiac 336

Hi everyone, new young member here.

I just finished rebuilding a 55 1st series GMC 1/2ton with my father and now I want one for myself

My dad is all about restoring to all original but of course I like the modernized classic style.

Here is our project
picture

I found an extremely clean 58 GMC 3/4 ton locally. It sat for 15 years, but I started it up and it runs great and even the brakes work although they are weak. It has a rust free cab but a flat bed.

I had my heart set on a 1/2 ton but this one is a great deal at $1000. I found a fleetside GMC bed locally for $450 as well that I might pick up.
It has the original 336 pontiac, 4 spd, and large rear window.


My question is how good of a candidate is a 3/4 ton for a custom truck? I'm worried about the bed length, I would like to shorten it eventually.

Is there any downsides to using the 3/4 ton? I would update the suspension both front and rear.

Also the pontiac 336 motor has extremely limited information on the internet. I'm wondering if SBC motors are a direct swap if I get a matching transmission.

Thanks for all your help and I'll be around here reading for the next few months to catch up. Awesome website you have here

a 3/4 ton is a nice truck if you are going to leave original, or do small mods to, a 1/2 is easier just because they make more aftermarket supsension, and brake set ups, to shorten the 3/4 you'll have to cut the frame or find a 1/2 ton short anyway, i am a fan of longbeds and original so i would get the 3/4, but for what you are planning on doing the 1/2 may be better suited

oh and very nice pic also, i like the color

There is nothing wrong with a 3/4 ton or a Pontiac engine. It may be geared too low for a daily driver. I don't have a GMC book but the same year Chevy would have a 4:57 rear end.
Also, I think GMC mirrored Pontiac with engines so a 58 could be a 347. You could use your 4 speed trans with a SBC with the Chevy bellhousing. You would also need mounts, exhaust, and other incidentals. It seems like a lot of work & expense for little gain.
Fred

The major difference between 1/2 and 3/4 tons would be the springs. The AD trucks front end seem to be identical; I'm not sure if the 58 is the same. You say you're going to update the suspension so that shouldn't matter. After updating front and rear you've pretty well made it a 1/2 ton. Now you will need to decide if you want to cut the frame down to short bed.
Have fun and welcome to the bolt.
That's what it's all about anyway.

If my memory is any good at all, Pontiac changed engine displacements every year in the mid/late 50s.

55=287, 56=316, 57=347, 58=370, 59 the famous 389.


Great engines. Keep it. Should be lots of used speed parts around as these were fast an popular in the day.

This falls into the category of one of them good problems...

There are a bunch of guys better qualified to answer this than I am. That said, I believe you'll find the 3/4 ton frame to be a little beefier than the 1/2 ton. The rear end is likely to be beefier as well and could well be same rear end as was used on one tons. It is geared real low and there are no aftermarket gears for that thing. I'm of the view that the 3/4 ton is a great truck to restore and perhaps upgrade for some kind of heavy use. And you have a good one there for that given the fact it's a bigger GMC with a big motor. I'm not one of those guys who hates it when someone hotrods a bolt. If that's what you like go for it. I do feel that a half ton is better for that. Find one with the frame already short and your project will be much easier. Most guys like to lower them and make the ride more like a car. Why do that with a big old 3/4 ton? There's no disc brake kit for a 3/4 making that a PIA. MUCH easier to do that and more to a 1/2 ton.

That said, buy that truck. Now that you have experience working on them, noodle around with it, clean it up, get it running good and flip it. You'll find guys lined up from here to Jerusalem to buy that thing off you. Meanwhile you can shop for a 1/2 ton that will be easier to hot rod out.

Let us know. There'll be a bunch of guys that want that truck!!!!

Welcome to the bolt. If you haven't already you should submit that picture and a write-up about your dad's truck to Peggy, the admin of this site so she can put it in the Gallery. COOL!

I'm always one for keeping a 3/4 ton truck as a 3/4 ton because they were made for work. If it's anything like the AD and earlier trucks, you might be better getting a donor chasis for it and making it into a 1/2 ton. The engine sounds like a keeper in any case. A stock looking 3/4 ton "remodeled" for speed could make for a nice "stealth" street rod.

While I am attached to the larger trucks as not nearly as many were made, they do not command the value of the 1/2 tons .... for now.

I think you'll find a Spicer(Dana)60 rear under that truck. Same rear as some muscle cars in the 60's I think.
Welcome to The Stovebolt.
Jeff

As one that is in the process of a frame-off restore of a 3604, a 3/4 ton I can say with authority that the only difference between the 3/4 and the 1/2 is the placement of a rear cross-member and heaver springs. Bambrose said he wanted to upgrade with a new IFS, new rear end and rear springs. When he swaps out springs and upgrades his front end and his rear he now has transformed that 3/4 ton to a 1/2 ton. The 3/4 frame is not beefed up or heaver than the 1/2 ton frame. Check mine out.
http://good-times.webshots.com/photo/2468275250099708909yMPppY

Thank you everyone for the information.

I'm going to take a look at the 58 tomorrow and I'll be bringing along my camera to snap some pictures. I'll update and post them on Sunday evening.

ok thats sounds like a good idea

I have not visited this discussion since March so I guess it's old news but I have to disagree with BIG CHEVY about the 3/4-ton frame. The frame C-channel rail is heavier, taller, thicker and has a greater section modulus and thus stronger than the 1/2-ton as evidenced by this page from the resto pack. This is my third A-D 3/4-ton and I know a little about them.
I have no knowledge about the 1958 GMC 3/4-ton frame that bambbrose asked about. Maybe it is the same as a 1/2-ton but probably not. Good luck bambbrose with a truck- let us know what you get- and good luck Jim with your 51- it's a cool old truck.

Frank's right on the frame. The major difference you will face with rear suspension is most suppliers will ship parts for a 3100 which may not fit the 3/4 ton. I have had to do some fabrication with TCI's rear spring kit and for the rear anti-sway bar because the 3/4 frame is more narrow.

On the '55-'59 chassis, the frames are much closer in construction than on the earlier trucks. They maintain a 34" dimension across the fram width. The primary differences are in the length and the thickness of the material. For the most part, 1/2 ton suspension peices can be swapped directly into a 3/4 ton chassis. The front suspension is virtually identical, only having a few more leaves and the axle forging and spindles are heavier. On the rear, there's not really much difference other than the axle, depending on how the truck was optioned. The base 3/4 ton uses the same springs as the heavy duty option on the 1/2 ton. Take a good look under a 3200 sometime, they're essentially a 3/4 ton with 1/2 ton axles and brakes. Sort of. The front hydraulics in a 3200 are the same as 3/4 ton.
I would also suspect that the GMC would have the Spicer rear as well. If it does, that makes things much simpler in the gear department, as there's lots of gear choices available for that diff.