The Stovebolt Site Forums The Parking Lot Big Bolts 40 rear end question

question? i have a 1940 GMC 1&1/2 ton and i'm wanting a higher ratio rear end.is there a newer model rear end that will bolt up to original rims.

You'll need to go to open driveline if it's like a chevy. What is the tooth count for your rear end ring and pinion ? There were two ratios. What size tires are you running and how fast are you looking to go ? Check out the Gallery, go to Lou MacMillans '37 1 1/2 ton, scroll to his tech tips, scroll to '37 trux page. Nice chart of gear ratios, tires, engine speed, and MPH, plus more.

i'm not sure but i think it's the same as chevy.what i have is a open drive shaft with at least 6 to 1 ratio with 2 speed axel with original 20" rims.motor has been changed to 5.9 cummins with 5 speed trans.i'm going to use it to pull my 42 1/2 ton .65 is plenty fast .kinda looking change it out to 3.54.

Try jumping over to the "crashbox" forum. Some of those guys really know their stuff about what will change out for what. 65 MPH is faster than I would want to push that truck without a bunch of upgrades. At least the front end and brakes want to be in first class condition. What I know about the 2 speed rears is that they are slow 6:1 and slower. I think the stock "faster" single speed rear is 5.2:1. Then there's more modern wheels and radials too.

if you have the timkin rear then a rear swap is in order not just a ring and pinion.