1500 to 2500


Junior Member
orlando, fl.
Hello, I have a 1985 gmc C1500 with a 350 and a 400 tranny. I would like to know what are the diffrence between 1500 and 2500? What would I have to swap in to make it a 2500. It originally came with a 4.3 v6. It also seems to have bed sagging on the drivers side, body/bed mounts?Any info good, thanks.


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In that era, to the best of my knowledge there were two different types of 2500 (3/4 ton) Chevy trucks: What I call a "light 3/4" and a "heavy 3/4". I'm pretty sure the actual frames were the same.

Both use 8 lug wheels, but the "heavy" one has a full-floater rear axle while the "light" version has a semi-floater one. You can tell the difference between them by the big hub that sticks out past the wheel on the full-floater, plus the rear brakes are bigger. Also, to access the brakes on a full floater axle you have to remove the hub and drum as a unit.

Up front, spindles would be different because a parts catalog I'm looking at shows a different number for the 1/2-ton and 3/4-ton. (3/4 and 1-ton show the same part number)

Different catalog for front end parts shows different ball joints/control arm bushings, although the steering stuff is the same.

So there's actually more than meets the eye to making the swap.

As far as the box sagging, they are just formed "tin" and the crossers that bear on the frame may well be a bit "crushed" from years of use. Rust may/may not be a factor. If the box is solid, you can shim the low areas up. If it's rusted, either weld in new tin or replace the box altogether.

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