47-55.1 50 GMC 1 ton to 1/2 ton conversion??

[68c10owner]

I found a 50 GMC local for a good price. Only issue is it's a 1 ton and I've been looking for a 1/2 ton. The front fenders and sheet metal looks the same on this one but are the frames themselves similar? Can I remove the original 1 ton suspension and add a Mustang II crossmember? I could look for a different chassis but I don't mind doing the work if I can repurpose the original.

[dsraven]

welcome to the forum.
does your truck have single or dual rear wheels
mr48 is gonna be your 47-55.1 expert.
have you done any research on the independent front suspension models and manufacturers, their starter packages and their upgrade packages?coils or air bag springs, size of brake rotors, brake upgrades and how they affect wheel sizes that can be used, control arm tubing size and wall thickness, ball joint style and quality, tie rod end quality, power steering upgrades, cross member steel thickness, etc? there are some important things to consider when doing a comparison.
first I would recomend to put together a want list list and go from there. think about what you want the truck to look like and what purpose it will serve. like, will it be a lowered truck or do you like the stock height. what will you use for a drivetrain. what will the use be mostly, daily driver-high performance race use-show truck-etc.consider the track width of the IFS you choose and then think about how that will affect the style of wheels you can use-deep dish or not-and compare to your wish list
if you can, post up a few pics of your project. there is a "how to post pics" thread if you are unsure how to do that. we all love to see the pics and answer any questions you may have. there are some who may have parts you need, once you get started, but in order to advertise you probably need to join as a "paid member" or send private messages to those who may respond with "I have one of those"

[Ziegelsteinfaust]

The frame width's are the same, but the height and thickness will be different. Along with the kick ups or frame height taper being different. Which really doesn't matter.

They only made 1 cab and 2 different sets of fenders for the 1/2 to 2.5 ton I believe. I am not up on the bigger trucks.

My friend got a 1955 2 ton GMC with the 300 Jimmy 6 for $1000 for the engine initially. Since he wanted a 55 anyways. I convinced him to let me "fix" the truck for him. As I was going do most of the fab work anyways. Luckily he settled on a 1 ton suspension, duals in the rear, and a flat bed. But a Camaro clip or M2 set up would of been just as easy.

I sectioned the frame from 10 or so inches to 4-6. The frame was 5/16" thick roughly. Then slammed it as much as possible with a new straight axle for the front from a 90's HD 8 lug truck.

[studeclunker]

Well, I can understand why you don't want to drive a one-ton of that era. I have a '58 (top speed 45 mph) rides like a truck for some reason. Why don't you just frame it over to a comparable modern 1-ton frame? Or are you looking for all show and no work?

[mr48chev]

I'm not the expert I just know how and where to find the info. 51 years of working on them doesn't hurt though.

There isn't a lot of specific info on GMC trucks but all 1/2, 3/4 and 1 tons have the same front sheet metal outside of year specific changes. A conventional cab is a conventional cab and the only difference is the 1-1/2 ton and larger often have more holes in the firewalls for plumbing for Air shift for the 2 speed rear axle or other items that little trucks don't have.

All of the conventional cab trucks have the centerline of the front axle 17-3/4 from the flat of the firewall. 1 ton springs are 2 inches longer and a quarter inch wider than 1/2 or 3/4 ton springs. I am thinking that most of that length is in front of the axle though and that messes with the Measure from the center of the front spring bolt in the frame 18-1/8 inches to the axle center line. You will have to figure out exactly where the center lines and mark it on the frame and have notes and drawings with your reference points. Frame measurements so you can compensate for the difference will have to be dug up but if I get the nose off my 48 quick enough I can provide those with photos and drawings.

I haven't decided if I am going MII or Jag XJ on mine It may be Jag though. as I have one that is pretty well trimmed to be fitted up to my frame.

The rear of the 1 ton frame is Pretty much straight and flat and if you lower the rear much you will need to put a C notch in the frame. As far as setting up the rear suspension the good is that the frame rails are straight from the cab all the way back Making it simple to do spring or suspension swaps.

[68c10owner]

Originally Posted by dsraven

welcome to the forum.
does your truck have single or dual rear wheels
mr48 is gonna be your 47-55.1 expert.
have you done any research on the independent front suspension models and manufacturers, their starter packages and their upgrade packages?coils or air bag springs, size of brake rotors, brake upgrades and how they affect wheel sizes that can be used, control arm tubing size and wall thickness, ball joint style and quality, tie rod end quality, power steering upgrades, cross member steel thickness, etc? there are some important things to consider when doing a comparison.
first I would recomend to put together a want list list and go from there. think about what you want the truck to look like and what purpose it will serve. like, will it be a lowered truck or do you like the stock height. what will you use for a drivetrain. what will the use be mostly, daily driver-high performance race use-show truck-etc.consider the track width of the IFS you choose and then think about how that will affect the style of wheels you can use-deep dish or not-and compare to your wish list
if you can, post up a few pics of your project. there is a "how to post pics" thread if you are unsure how to do that. we all love to see the pics and answer any questions you may have. there are some who may have parts you need, once you get started, but in order to advertise you probably need to join as a "paid member" or send private messages to those who may respond with "I have one of those"

Thanks but ive been a member since 2003. I just haven't been active in a long time.

I don't have the truck. I found one and since I don't know anything about the 1 t9ns I wanted to ask about it before I spent money on it. I know all about the suspensions available for these. I just needed to know about converting a 1 ton to a 1/2 ton.

[68c10owner]

Originally Posted by Ziegelsteinfaust

The frame width's are the same, but the height and thickness will be different. Along with the kick ups or frame height taper being different. Which really doesn't matter.

They only made 1 cab and 2 different sets of fenders for the 1/2 to 2.5 ton I believe. I am not up on the bigger trucks.

My friend got a 1955 2 ton GMC with the 300 Jimmy 6 for $1000 for the engine initially. Since he wanted a 55 anyways. I convinced him to let me "fix" the truck for him. As I was going do most of the fab work anyways. Luckily he settled on a 1 ton suspension, duals in the rear, and a flat bed. But a Camaro clip or M2 set up would of been just as easy.

I sectioned the frame from 10 or so inches to 4-6. The frame was 5/16" thick roughly. Then slammed it as much as possible with a new straight axle for the front from a 90's HD 8 lug truck.

The height of the frame is what I'm concerned about. I had a suspicion that it was a taller frame. I'd have to see how that would effect adding a MII crossmember

[68c10owner]

Originally Posted by studeclunker

Well, I can understand why you don't want to drive a one-ton of that era. I have a '58 (top speed 45 mph) rides like a truck for some reason. Why don't you just frame it over to a comparable modern 1-ton frame? Or are you looking for all show and no work?

As I mentioned in my original post, I've been looking for a 1/2 ton. So I've got no desire to swap it to a modern 1 ton chassis. I wouldn't be building this for a work truck anyway. I'm a truck driver and use the company equipment. And I daily a 2015 Silverado for whoever I need a truck for personal use. This would be a hot rod build.

[68c10owner]

Originally Posted by mr48chev

I'm not the expert I just know how and where to find the info. 51 years of working on them doesn't hurt though.

There isn't a lot of specific info on GMC trucks but all 1/2, 3/4 and 1 tons have the same front sheet metal outside of year specific changes. A conventional cab is a conventional cab and the only difference is the 1-1/2 ton and larger often have more holes in the firewalls for plumbing for Air shift for the 2 speed rear axle or other items that little trucks don't have.

All of the conventional cab trucks have the centerline of the front axle 17-3/4 from the flat of the firewall. 1 ton springs are 2 inches longer and a quarter inch wider than 1/2 or 3/4 ton springs. I am thinking that most of that length is in front of the axle though and that messes with the Measure from the center of the front spring bolt in the frame 18-1/8 inches to the axle center line. You will have to figure out exactly where the center lines and mark it on the frame and have notes and drawings with your reference points. Frame measurements so you can compensate for the difference will have to be dug up but if I get the nose off my 48 quick enough I can provide those with photos and drawings.

I haven't decided if I am going MII or Jag XJ on mine It may be Jag though. as I have one that is pretty well trimmed to be fitted up to my frame.

The rear of the 1 ton frame is Pretty much straight and flat and if you lower the rear much you will need to put a C notch in the frame. As far as setting up the rear suspension the good is that the frame rails are straight from the cab all the way back Making it simple to do spring or suspension swaps.

I appreciate the info. I thought I had heard the 1 ton chassis were taller. Sound's like I'd be better off continuing my search for a 1/2 ton or at most a 3/4 ton.

[mr48chev]

I reread your original post again and even though the frame is heavier if you have the skills you can shorten the wheelbase to 116 inches, C notch the frame and put a short bed box on it. One of the 68/72 guys did a shorten the frame by making an overlapping connection rather than a straight cut off and butt weld connection.

This is his drawing that I saved. If I didn't need a 3/4 ton truck to tow my boat and car trailer I'd convert my 71 GMC 3/4 ton to a short box 1/2 ton.

The main thing is come up with a workable plan that is within your budget and your skill level.

[68c10owner]

Originally Posted by mr48chev

I reread your original post again and even though the frame is heavier if you have the skills you can shorten the wheelbase to 116 inches, C notch the frame and put a short bed box on it. One of the 68/72 guys did a shorten the frame by making an overlapping connection rather than a straight cut off and butt weld connection.

This is his drawing that I saved. If I didn't need a 3/4 ton truck to tow my boat and car trailer I'd convert my 71 GMC 3/4 ton to a short box 1/2 ton.

The main thing is come up with a workable plan that is within your budget and your skill level.

I'd definitely be shortening the frame. That wasn't my concern. I was worried that the frame height was different which would throw off the geometry of the Mustang II suspension. I dont need a truck for towing or hauling. I just prefer to drive trucks. And I prefer shoetbed 1/2 tons. But a good shortbed 47-54 truck is getting pricey these days. I can find long bed 3/4 tons much more reasonable. This 1 ton popped up for $900 but I'm going to pass on it.

[dsraven]

if the cab and fenders are the same as the 1/2 ton it may be a great start for a 1/2 ton short bed project. its getting hard to find a good cab these days that hasn't been butchered over the years or that isn't rusted out everywhere. lots of the rougher riding trucks got left for work projects rather than daily drivers due to their teeth jolting ride with no load. that meant that these trucks got less miles on them especially in winter driving conditions, should that have been an issue where they "grew up"
just a few questions, to get to know your wants and skill set as well as what you have to work with.
what do you plan for a finished project
what kind of skills do you have as far as mechanical, electrical and metal working
what do you have for work space available and area for parts storage-large itmes like cab, box, front sheet metal etc
would you be doing a body off frame, complete rebuild/modification/paint or are you more interested in a mechanically sound patina truck