Is there a difference between 2wd and 4wd frame other than spring mounts?

[akcheyenne]

I bought a 72 cheyenne over the net and had it shipped to me. My error I know, Now that I have gotten past kicking myself I have found that the frame has been cracked and welded by power steering assembly. I know this is common but would I have worked hard to straighten the body and the frame does not appear to have been welded correctly. I have found a 2wd frame and am wondering if I switch the leaf spring mounts is there anything else that will catch me off guard???

[trukman1]

Most Chevrolet frames came standard with coil-spring rear suspensions which have a wider rear frame dimension in the rear while leaf springs were an option. Most GMC trucks were produced with leaf springs as standard and coil springs optional. The frames of the coil spring trucks are different (wider) than the leaf spring frames. Take your tape measure or refer to a Factory Service Manual for more detail. One oddity, early GMC frames are shaped different than '69-up Chevrolet frames and some '67-'68 frames with coils had the same frame that could accept leafs using the GMC mounts...but these situations are rare. Don't be regretting your second frame, measure the frames and compare to existing trucks or manuals to be sure your getting what you want. My .02 cents worth.

[Gee_Emm]

Cab mounts

[Fast68Chevy]

i dont know about the gmc thing,
but 2wd 1/2 and 3/4 frames regardless of coil or G70 leaf rear have the rear 38.5" outside width directly above axle,

4x4 and 1 ton dont have this spread out over the axle back there, reason being is because no 4x4 or 1 ton are coil rear

you can put leaf hangers on coil frame or the coil trailing arm brackets anmd spring retainers on leaf frame, and also swap the crossmember for each style rear over to either chassis, are same dimensions, just differet design crossmembers is all.

good luck

[tom hand]

I would cut the piece you need from a donor frame and have someone that knows what they are doing weld it to your frame.

[toms68cst]

If I remember right the 1/2 ton 2wd frame is not made out of as heavy steel as the 1/2 ton 4X4. They may look similar and be the same shape but it's not as heavy.

I'd find a good factory 4X4 frame especially if it's going to be lifted and/or used off road.

[JimKshortstep4x4]

Since I have not seen the crack, this suggestion may not be applicable. Some of the Blazers and 4x4's came with reenforcement plates riveted in place at the mount location. You might be able to use one of these and make a proper repair.

Jim

[akcheyenne]

Thanks for everyone's input. I do appreciate it.

[trukman1]

Just for the record...

1) The coil spring frames I have checked have all been wider at the point where the front mounts for leaf springs would mount.
The factory service manual frame dimensions also support this.

2) There is no difference in the thicknesss of 1/2 or 3/4 ton trucks.
For that matter, there is no difference in Chevy to GMC thickness.
All start out on the same assembly line, same plant.

Just for the record...

[toms68cst]

What does this mean from the 70 spec sheet I have then?

1/2 ton C10 Section Modulus is 2.98

3/4 ton C20 is 3.71

1/2 ton K10 is 3.48

Is section modulus related to the frame thickness or not?

[JimKshortstep4x4]

The frame section modulus is a measure of the frames ability to resist twisting and can either be done by thickness changes ,
material changes, heat treatment, or a combination of these.

Thickness can be compared, but checking the metallurgy of the frame material for comparison could prove to be difficult unless one has access to a metallurgy lab.

Jim

[Stout72]

Last month's 4 Wheel Drive magazine ran an article on how to fix the frame cracking problem IWO the steering box, and showed a product used to stiffen up this inherently weak area. Check it out.

[trukman1]

All I know about this is the modulus MAY be affected/determined by the crossmembers, placement and thicknesses since they are different on the vehicles I have measured. However, I have yet to find any difference in the actual wall thickenss of the C-channels themselves. From what I can see, the 2wd trucks have more crossmembers and thicker ones at that. This would, I think, make the frames more rigid and less able to flex which, flex is what I would want in a 4x4 frame. This does not however mean a weaker frame since the frames that flex would theoretically be more resistant to fractures with their increased flexibility therefore rating as having more a greater overall strength. This would be my only reasoning to the increased modulus ratings. Again, I only measured frame thicknesses at the C-channel as a test to see if indeed there was a difference in frame thicknesses, of which I have yet to see a difference in that one measurement. I do know the crossmember on my 2wd '67 are thicker and more numerous than on my '69 K20. Hope this adds to the information base without causing more confusion. I just got curious after hearing that the frame thicknesses were different and began measuring them out of curiosity. Gary

[toms68cst]

Good description folks. i always thought that modulus rating had to do with thickness/heaviness of the frame. I've heard others say that too.