The Stovebolt Site Forums The Shop Area The HiPo Shop rear end swap suggestions

I am putting in a 350 small block ( approx.190 hp)into a 1956 GMC 3/4 ton.Looking to replace the 4.56 rear with something highway friendly....looking at a rear end from camaro nova or chevelle.....not sure about 308....273....256 rear gears....do not have a transmission yet so I was wondering about the right set up (overdrive or not)..I am looking to make this a highway cruiser...not sure if overdrive will lug the motor....any suggestions??

A 3.73 rear end and a 700R4 transmission is a good combo with 28-30 inch tires.
A 3.08 rear with a TH350 or TH400 would be my second choice.

Be aware that a Chevelle/Nova etc rear end would be 5 lug vs the 8 lug front end on a 3/4 ton truck. Providing that your GMC has the same corporate rear end as a Chevy of that era you could obtain a 4:10 replacement from a 67-72 GM truck. That would also work well with the 700R4 transmission. You could still attain highway speeds and still use it as a truck.
Fred

Thanks guys....as I had already replaced the front end with 5 lug as the 3/4 ton tie rods ends tend to limit wheel selection and the 8 lug original wheels were split rims.....this truck will only be used as a cruiser....I have considered a 700r4 with o/d but was afraid with a 308 it might be too low a number and might lug the engine....I am thinking 308 with 350 trans might do the trick....thanks for the input...

What is the WMS-to-WMS of your stock axle?

I would think that the Camaro/Nova variety would be too narrow for a 3/4 ton, but I don't know much about the later GMC trucks though...my '50 3/4 ton had an axle considerably wider than the standard 1/2 ton (63" wide).

The rear end is 62.5....from what I have found the same as a 68-71 Chevelle.......

The 700 with a 3.73-4.10 rear would give you far more flexibility than the 350/3.08 combo, especially with a relatively low horsepower engine. The better first gear ratio is better for getting it going, and the overdrive ratio for the highway. Best of both worlds.

nj56gmc, I went back and looked at all my notes and that is the same 62.5 measurement that I took for my '50 3/4 ton axle.

Finding an affordable Chevelle axle would be nearly impossible around here, so I didn't even consider it (now that they are considered to be $20-30k cars!!).

I ended up finding a 10 bolt 8.5 ring gear GM axle that was 63.0 wide, but it is GM metric, so although the bolt pattern is the same, the lug nut threads are different on the rear of my truck! It's a1998 Chevy S-10 Blazer ZR-2 axle. It comes with 3.73 gears and a G80 locker (I tossed the locker). The swap required me to R&R the shock mounts and spring perches, and use different U-bolts with a flat spring plate on top of the spring. Way more work than I wanted to do. I guess the Chevelle axle might have been easier..

Great info guys!....it looks like a 3.73 with 700r4 might be what I am looking for....and so the search begins.....

I ran a 700R4 with 3:08 rear with a 350 stock engine in a 70 1/2 ton step side for several years. It was a beautiful driver. The engine settled down on the highway & was quiet. It got 18 mpg. & would pull long hills on the interstate easily with A/C on. That's the only way I would go.
George