Welding 2500 rearframe onto 1500 frame?

[Barrymaxx]

Hey everyone

New here but not new to these trucks. I have a 98 gmc sclb. The rear of the frame is in terrible shape. Its to the point where its easier and safer to graft a new frame onto this one. Likely just forward of the last cab mount/first bed mount.

So, I can get a 99 2500 obs 8 lug rear frame cheap and easy. Its in really solid shape too.

I hear rumors that the frame is thicker, which I beleive is true. Others say it is taller as well. Does anyone know FOR SURE if it is? According to the gm drawings it is not but who knows.


Does anyone see any problems with me doing this? Here are the things that concern me:

The rear springs are longer? So I need to move the mounts or use 2500 springs?

Are the shock mounts taller? It looks like 2500 shocks are longer than mine. Are tthey not?

Will my 1500 trailer hitch bolt up?

The frames look the same shape. So even if it is taller I could just build a gusset at the bottom to transition into the shorter 1500 frame.

Does anyone see anything im missing before I cut my truck in half?

I have attached the gm drawings. It looks like the nose of the 2500 frame is a tad longer but that shoudnt affect me here. Other changes are just transmission related..

 

[Barrymaxx]

Edit: Just realized that image is stupid small and useless. Its from page 82 of the gmt400 pdf

 

[RyanMerrick]

Why not just get a whole frame and transfer everything onto it?

 

[Barrymaxx]

Its a lot of work and the rest of the frame is solid somehow. its like this truck was hung from a crane and dipped in salt water ass first its whole life. Rear cab mounts forward is solid metal.

 

[RyanMerrick]

Haha, well everything on the 2500s and 3500s are a lot beefier from brakes to springs etc. I don't know what a 1500 looks like underneath but if you need any pics of a specific part of a 2500, let me know.

 

[891Ton]

I would take a tape measure and go find out for sure. Dont rely on what people think because for some reason these trucks are all a little different. I fab parts for people and I will take the a bumper and try to put it in the same style truck as another one and it wont fit. Weird stuff like that. The frames are all off a little here and there. I swear its like each plant tools a little different or something. Just something Ive noticed over the years. So if you can just take some measurements, and then go to the salvage frame and measure it up too. Thats the only way I would even consider buying something like that.

 

[AlNelson]

I believe frames that were under 8600 GVWR were the same. Thats what ive heard anyways.

 

[RyanMerrick]

I believe frames that were under 8600 GVWR were the same. Thats what ive heard anyways.

I don't think that's accurate

 

[benz88]

Mines getting rusty Also at the back where the spare tire crossmember mounts. So What Im doing Is building a new section out of 2x3 tubing from around the axle back inside the frame rails like this. The Red is the box tubing and the Green is the crappy stock cross member which I'll probably delete. Black is stock frame

You must be registered for see images attach

 

[axisT6]

From my hands on experience, the 8 lug 3/4 ton chassis is thicker. The chassis rails are taller under the cab and are most likely a bit taller in the bed area. ALL 88-98 truck springs are the same length. The exception is the 3500HD.

The 6 lug 3/4 ton chassis is near if not exactly identical to the 1500. The difference is the rear axle and the springs.

To make life easier, easier, either swap chassis, or find an identical chassis.