The Stovebolt Site Forums The Shop Area General Truck Talk 1/2 ton or 3/4 ton

How do I know I have a 1/2 ton or 3/4? The truck I bougth is sort of a mix of years, cab and frame definetly 49 or 50. 4 speed GMC, no plate on door frame, no ID number on the frame. Something special to look for than can show them apart?

1/2 tons have 6 lug wheels, 3/4 ton are 8 lug. The 1/2 ton also has a completly enclosed driveline on that body style, 3/4 ton are enclosed to the carrier bearing, then open to the rear axle, which is also much larger than 1/2 ton.

The truck has 6 lugs, but I don't get the driveline part. If you give me a copule of minutes I'll upload a photo of the drive line.

Thanks Longbox

Dear Longbox, attached is the link for the transmission, sorry they're rotated. Driveline and Transmission

Definetly 1/2 ton, but it looks like the rear is from a later 1/2 ton, as it is an open driveline. It's virtually identical to my '55 2nd, exept I don't have the slip-joint in the driveshaft and my truck has a 3 speed with the overdrive.

The engine number is A228212844, but the casting says GMC-7 2324002. According to the motor number it should be a 228, but for the casting number a 248 (55 1st?). Since the truck is sort of a mixup, can the guy put a 55 transmission with the engine in the frame. Frame is defenitly a 53 because of the arch on the rear wheel.

It is quite possible you have the differential, housing and springs from a '55 first. The '55 1st rear end is a popular way to convert to open driveline because they will bolt right in in place of the torque tube assembly.

That engine casting number is a mystery though. I have a 248 with a 1955 date code with that casting number. I at first thought yours might have been a dealer replacement and the old titling serial number stamped on it. GMC replacement engines came with a blank serial number but the displacement was stamped on them. It's strange that one has 228 on it.

Are you the same guy who was showing pictures of a beautiful red truck that appeared to have parts from several different years on it?

If I'm thinking of the same truck it could easily be that no two major parts came from the factory on the same truck.

Having a truck assembled from different years isn't a bad thing unless you are trying to create an accurate restoration. And even then many parts are not identifiably different one year to the next.

Any GM truck type 4-speed from '48 to '67 could be in that truck and without studying the date codes it would be hard to tell it wasn't original. Actually only '67 has a backup light switch from the factory so those are unique unless someone has changed that cover.

If the frame and running gear were all original including the steering, a '53 is unique because of the early style kick-up an the later style drag link. However on your truck its probably not a safe bet the steering is original.

Many of the parts on these trucks are interchangeable across the entire '47 to '55 1st run. Others vary a lot year to year. Your challenge will be to learn which are which any time you actually need parts and to understand for which parts you actually care how accurate they are.

Looking at the pictures its clear the running gear parts have not been cleaned or refurbished in recent years. That would lead me to suspect they have been together a long time. Are things like the spring shackles or spring bolts either front or rear newer looking than the transmission or rear axle?

That definitely looks like an SM420 trans. Aren't all 3/4 tons longbeds?

GMC made a 1/2-ton long box truck, and the GMC serial number listing include 1-ton trucks in the 3/4-ton length.

So while as far as I know all 3/4-tons Chevy trucks of the AD era are either long box or flat bed, a long-box does not definitively mean the truck underneath was born a 3/4-ton.

The SM420 was not exclusive to any particular size of truck.

To add to that, GMC would build 3/4 and 1 ton trucks on the 1/2 ton wheelbase for specific customer needs.

Now you have me confused. Yes OldSub, I'm the guy with the 'mater, as in To-mater. I'm fine with the idea of having a salad of parts on the truck. I just want to identify different component, in case I need a change. For example, the idea of finding out if it is a 3/4 or 1/2 is knowing if the rear transmission is 4.57 or 4.11. I would like (in its due time) to be able to change that to a highway friendly ratio. I've read that a 4.57 might take a 62 Suburban transmission to become a 4.11, and a 4.11 1/2 ton, go with Patrick and make it a 3.55. Do you follow where I'm getting? Same is with the engine, just want to make sure to buy what its right for it, so thats why I need to identify, if not the year, the CID. Being not form the States, we have a very limited, if not closed to inexistent supply of old trucks. Maybe the guys who assempled the truck made it tastefully, but not necessarily right. Since I'm buying mostly from the US, I need to get my parts right, no chance for an easy devolution. Sorry for the long testament, buy I'm close to dispair. You guys have been of great help, but I guess I'm still a long way to go. Of course, happy to do it.

Don't get discouraged, we'll help you figure it out. Sometimes we may need to work your camera pretty hard to get it done.

If you have six lug wheels, which I believe you confirmed up above, you have a 1/2-ton. Or at least the significant parts of the drivetrain are all 1/2-ton even if other parts didn't start out on a 1/2-ton.

Six lug wheels equal a half ton on that era of truck. No other GM truck has the six lug wheels.

Eight lug wheels could be either a 3/4- or 1-ton. You don't have eight lug wheels so you have a 1/2-ton.

Given the open driveline you can not assume any of the drivetrain is stock. The rear axle and possibly more is later stuff.

The best way to know your axle ratio is to open the differential and count the teeth. The easiest way is to first put blocks in front and behind both front wheels, then jack up just one rear wheel and count how many times the driveshaft turns for each turn of the lifted wheel. Then do a little math.

Can I put math in a sentence? (number of drive shaft revolutions) divided by (number of tire revolutions) times 2 would give the approximate gear ratio. If you have 4.11 gears expect to see the drive shaft turn just more than twice for each turn of the wheel.

If your gears are 3.90 you'll see just less than two turns of the drive shaft for each turn of the wheel.

4.57 gears would mean two and a quarter turns of the drive shaft, so you do need to watch pretty carefully, because you'll want to see the difference between 2.05 turns and 2.28 turns. Not hard to discern if you are watching.

Most of us are here because we want to share what we know with others, so we'll enjoy helping you sort this out.

Thanks a lot OldSub. I really appreciate the help. I guess everybody joins in order to share experience and knowledge. Just that after being here a couple of months, feel more like a leech, just sucking knowledge, because I came to my senses that I'm close to knowing Zip. But I'm learning a lot. I'm Mechanical Engineering, but guess what, no hands on knowledge on vehicle mechanics. What makes it more difficult is that I don't have the truck in my possession and the pictures have been taken with my phone. I hope to have the truck in my job by tomorrow, I'll buy a good camera and keep sucking info form you guys.

Again, thanks a lot.

Hey Chinito, we all started with zero knowledge. When I started there was no internet to exchange the knowledge of others with. You have a huge advantage. Don't be ashamed of using it. Once you get your truck there and start getting your hands greasy and your knuckles skinned you'll start building knowledge to share. It will all even out.

Thanks again. You will be hearing form me soon and often.

Guess you heard from me sooner. GMCdp said that it might be a SM420 transmission from a 3/4 ton. In this link Rear Transmission Kip says there might been lighter 3/4 tons trucks with 6 lug wheels and 11 inch drums. I'm still chewing on the idea of a 3/4 ton, because the registration papers of the truck says 3/4 tons (they say also it is a 54 Chevy, when it is a 49-50 GMC). Living in the tropics, strange things can be done with such an old car (believe me that also for brand new ones, also), paperwise speaking. I mean, the motor number says it is a H54T #### and the frame is a 54P something. The guy that went to the local DMV just invented some numbers and Voila, he got a new registration, a title and license plates. Long story just to tell that the papers might not be right, but then again, where the hell did they got the idea of a 3/4 ton? Is it possible. Due to the fact that it is an open transmission, what year should it be from? Can this ring and pinion be installed? Randys Ring and Pinion

In the Advance Design era if its a Chevy, or New Design era if its a GMC, only 1/2-ton GM trucks had six-lug wheels.

In the Art Deco years, which precede your truck there may have been six-lug 3/4-tons and starting in 1988 GM again made six-lug 3/4-ton trucks.

But '47 to '55 1st, the period your cab and frame are from, there were no six-lug 3/4-tong GM trucks. Anyone saying otherwise doesn't know what they are talking about. It always annoys me when people guess or speculate about such things. Its not hard to look up details like this one in the original documents.

You can look up lots of these details in the Restoration Pack by clicking my link and find this out. It may not always list a detail the way you are thinking about it, but for something like the issue at hand it does show models and which wheels could come on them and how those wheels attach.

If you read the page about wheels you'll see that the model 3100 (1/2-ton) came with only one attachment possibility. Six-lugs. And no other truck had that same attachment. '54 Chevy truck wheels.

Your cab my have come from a 3/4-ton truck, but the designations that matter are the ones that affect what parts you order and being a 1/2-ton or 3/4-ton cab makes little or no difference in cab parts. It makes a huge difference in front and rear axle parts, the differential, the brakes and the rear gears.

While it makes a difference in the transmission if you are trying to restore the truck, you have an open drive SM420. That is enough to identify your transmission for buying parts.

It would take checking the casting for numbers to say the transmission could be original or could not be because most the differences are only in the bolt-on pieces.

The transmissions are both easy to swap and easy to convert. Looking to call the truck a 3/4-ton because it has an open drive line is ignoring how easy those elements are to change.

It is possible the transmission like the cab originated in a 3/4-ton. It really does not matter because GM used that same transmission with different hardware bolted on the output end starting in 1948 and through 1967 in 1/2-, 3/4-, 1-, 1-1/2 and 2-ton trucks.

My point is that it being an open transmission means nothing regarding the size of the truck or the year of the truck. The transmissions can be converted from one type to another and were used by GM in different configurations for 20 years. Basing identification of the truck on the transmission in a case like yours where its clear parts have been brought together from a variety of trucks is not going to give a useful answer.

Someone else said they recognized the rear axle as looking like their '55 2nd or perhaps a later Task Force truck. That would suggest the rear axle came with the bed you have. I'll let someone else answer the question as to whether those gears will fit since I'm not sure the details of those axles.

You can call the truck a 3/4-ton because that matches the paperwork. But with a short box and six-lug wheels it looks and will perform like a 1/2-ton and more important when you buy parts you need 1/2-ton parts.

Ok OldSub, identifiying the transmission is sufficent. As I stated before, I'm not anal about the exact specs, as long as the parts I order will, not only fit, but work. So, I'll have to check specs for the SM420 and look for ring and pinion that gives a better ratio that fits this. Is that right?

Well the rear might be a 55t, but I'm not the one to identify the old rear axle. I'm better with newer ones. In order to order the right gears you need to be sure you know what that rear is.

I just remembered I was out there and never measured the tail gates.

Do you think it would be a good idea to buy the assembly manual for the 47-53 chevy's? I already have the 1947-1959 shop manuals. Would it be too different if it is a GMC, I've seen Chevy/B¡GMC assemlbly manuals for 54-59 and 60 to some later year but the 47-53 is only for Chevy. Just out of sheer curiosity, why is it easier to find parts for Chevys and Chevy pickups than Gmc's?