The Stovebolt Site Forums The Shop Area The HiPo Shop 3/4 ton latemodel rear end

I just put a chevy 400 with a 350 transmission in my 53 chevy flatbed. the rpm's are really high, any idea what ratio i have and what my options are so i can go 60mph.thanks

4.57 most likley.

Its possible to find a 4.11 that is an easy swap, just drop out the center section and replace.

Otherwise you're really looking at an axle swap.

I do NOT know about the 3/4 ton but on my 52panel I dropped the torque tube and replace it with a pumpkin out of a 56 1/2ton. It gets me from a 4:11 to a 3.90 better but not what I really wanted. We'll see how it works out.
In the meantime I'm on the look out for what I believe is a 62 which is still 6 lugs and a 3.73 gear?? I need to do some more research but I think the pumpkin will fit in the 52...????? If not then I guess a complete rear end change would be in order.

Does anyone know much about the 62 interchange/ratio?

i was told to turn the wheel one time and see how many times the drive shaft turns. one turn of the wheel gives me a 2.25 turns on the drive shaft. dont dont what it tells me.

For an "open" rearend, double that number(2.25) and you get the true ratio (4.5)= the factory 4.57...Since the 3/4 ton has an open driveline in the back, I switced mine out with a early 70's Ford(narrowest Dana 60, 8-lug floater) I could find..switch and weld the shock mounts and spring pads and had to fiddle with the brake hose...mine's 3.73running after market Vector mags(9.75 wide on rear), with 31x10.5x16.5 tires,just clearing the fender.
The ford axles have a larger center than Chevy, so stock Chev. wheels won't fit.Very happy with the result!

any ideas of a donor year and vechicle.

Since you have a flatbed you could use just about any rearend you want. Any truck rearend other then a 47.5-55.5 would be a tad wider, but then w/a flatbed it really shouldn't matter if the rearend is a couple of inches wider as long as it's still under the bed.
I'd look at any truck w/an automatic trans, then just pick a ratio and go looking, personally I'd get a rearend w/gears in the low/mid 3's. It will still give you good pick up yet your motor won't be wanting to jump out of the engine bay because of high RPM's &&&& you'd be able to commit a crime by breaking the speed limits w/o a problem.
I did a swap years ago for a friend who had a 3/4ton, she wanted disc brakes & late model rearend. So I swapped out the 3/4ton front axle for a 1/2ton and used a reareand out of a mid 80 fullsize GM car. W/the stock motor & 4spd trans w/the rearend I put in the truck easily did 65mph w/out problems....Joe

Ironhead68, this is something you probably already know, but I'll add it in case it helps others.
My '67 3/4 GMC came original with the Dana 60 with 4.56 gears.
I ran across a late '70s Dodge 3/4 with big V8 and Dana 60. It was a pick-a-part so I got the 3.54 gears with posi carrier for $50. The GMC uses bigger u-joints and different spline on the yoke. One phone call and $20 and I had the right yoke.

3.54 Dana gears are not that hard to find, new or used.

That ratio works well with my 4600# 3/4, SM465 4 spd and 292.
Not the easiest gears to set up, but worth it for me.