2wd/4wd Frame Geometery?

[C&D Crew Cab]

I have an opportunity to drag home an early 80s Chevy 2wd to use as my Rockwell Mockup. I realize the fwd body mounts and cross members are different and that there are no shackle pivots for the front axle, thats no big deal. What is a big deal is whether or not the frame geometry is the same between 2wd and 4wd as well as 1/2 ton to 3/4 ton.

Its been my belief that changes don't happen until you get to the 1 ton, then the individual frame rails are a completely different pressing. But as far as 1/2 or 3/4, 2wd or 4wd, I believe the frame rails start out the same and just get different brackets, hangers and cross members depending on the end configuration.

Yes? No?

Thanks in advance.

Rock On!

 

[cybrfire]

Yes.

 

[C&D Crew Cab]

Yes.

Thanks. Guess I'll drag it home too.

 

[tRustyK5]

The front portion of the one ton frame is also similar, it's only starting underneath the cab that it gets fairly different.

Rene

 

[C&D Crew Cab]

The front portion of the one ton frame is also similar, it's only starting underneath the cab that it gets fairly different.

Rene

Ah Ha! I did not know that. Good info, thanks.

 

[bigblazer20]

Actually the frames are different. The rails them selves are shorter (the up and down height of the [ ) on 2wd than a 4wd. I’ve done a lot of measuring while planning to do a 4wd conversion on my 82 Chevy. I've measured a '81 blazer, '86 k30, '79k20, and a '87 half ton burb 4wd and all were similar, but different height than a 2wd. So you cant us a 4wd engine crossmeber in 2wd with out modifying it.

 

[C&D Crew Cab]

Actually the frames are different. The rails them selves are shorter (the up and down height of the [ ) on 2wd than a 4wd. I’ve done a lot of measuring while planning to do a 4wd conversion on my 82 Chevy. I've measured a '81 blazer, '86 k30, '79k20, and a '87 half ton burb 4wd and all were similar, but different height than a 2wd. So you cant us a 4wd engine crossmeber in 2wd with out modifying it.

Interesting. You're saying that the "Web height" is shallower on a 2wd frame. Thats surprising. Given that both vehicles are the same load rating I wouldn't have predicted a structural change between 2 and 4wd.

Thanks.

 

[howdiy]

The frame is about an inch shorter where the engine mounts go into it

Heres my 2wd to 4wd conversion

http://www.pirate4x4.com/forum/showthread.php?t=700682

 

[C&D Crew Cab]

The frame is about an inch shorter where the engine mounts go into it

Heres my 2wd to 4wd conversion

http://www.pirate4x4.com/forum/showthread.php?t=700682

That is a really cool thread of your build. Fantastic pics, fantastic job.

As far as the mockup truck, I've passed on the 2wd because a buddy of mine is giving me the hulk of a 3/4 4wd that I sold to him that he parted out. It's just the frame and a few other pieces, but thats all I really need.

Thanks again!

 

[blazin_blazer]

if converting a 2wd to 4wd, could you leave the 2wd cross member in the 2wd frame and torch/plasma/sawzall (your pick) the cross member flush w/outside of the frame rail on both sides? (like this [_____] ) basically remove the coil buckets and the control arm mounts with a torch or saw and then box in the ends of the crossmember where you cut the 2wd cross-member off, & grind it up nice, & use the bottom of the boxed 2wd cross member to mount your bump stops, then make it ready for leaf springs up front? am i overlooking or forgetting something?

if i had a 2wd frame in my face right now, i prolly could answer my own question. i will look at a 2wd frame and cross member & a 4wd setup tomorrow & see what would stop you from being able to do this! i know your alot better off starting out with a 4wd frame & cross member, but some people don't have the means or that option & need to make what they have work, even if its a 2wd frame & cross member. I was just curious if cutting the 2wd cross member flush w/ the outside of the frame rails could be done & work out OK! ... [_____] you would more than likely have to use a huge amount of lift, b/c the 2wd cross member hangs down under the frame quit abit inboard of the coil buckets where it would need to be boxed. maybe you could cut it horizontally there and box it in flatter also...

i know sounds like alot of work, but alot of people are not as fortunate as some of us on here, who have a dozen+ gm trucks of different varieties sitting out on the back 9! after re-reading all this, it would prolly be less work to just build a custom 4x4 cross member that would fit in the 2wd frame!

 

[tRustyK5]

Yeah, the 2WD stuff just unbolts...so making a custom crossmember after ditching all that junk isn't too much work.

Rene

 

[4x4_76]

if converting a 2wd to 4wd, could you leave the 2wd cross member in the 2wd frame and torch/plasma/sawzall (your pick) the cross member flush w/outside of the frame rail on both sides? (like this [_____] ) basically remove the coil buckets and the control arm mounts with a torch or saw and then box in the ends of the crossmember where you cut the 2wd cross-member off, & grind it up nice, & use the bottom of the boxed 2wd cross member to mount your bump stops, then make it ready for leaf springs up front? am i overlooking or forgetting something?

if i had a 2wd frame in my face right now, i prolly could answer my own question. i will look at a 2wd frame and cross member & a 4wd setup tomorrow & see what would stop you from being able to do this! i know your alot better off starting out with a 4wd frame & cross member, but some people don't have the means or that option & need to make what they have work, even if its a 2wd frame & cross member. I was just curious if cutting the 2wd cross member flush w/ the outside of the frame rails could be done & work out OK! ... [_____] you would more than likely have to use a huge amount of lift, b/c the 2wd cross member hangs down under the frame quit abit inboard of the coil buckets where it would need to be boxed. maybe you could cut it horizontally there and box it in flatter also...

i know sounds like alot of work, but alot of people are not as fortunate as some of us on here, who have a dozen+ gm trucks of different varieties sitting out on the back 9! after re-reading all this, it would prolly be less work to just build a custom 4x4 cross member that would fit in the 2wd frame!

I was going to use stock 2wd crossmember on my build, but after lot of cutting, I found out that it would be ten times easier to build a custom x-member.

You right about the huge lift, because the 2wd x-member would hit the front axle.

But about the front x-member, 4wd one does not fit to 2wd frame, they seem to be curved differently (frames). If you mount 4wd x-member to a 2wd frame (RH rail), drivers side is way off.