The Stovebolt Site Forums The Shop Area Driveline Need Some Help Ref T5 Choices

For one more opinion, I chose to use a 3.07 Chevy rear end 12 bolt from 1969. It wasn't an accidental choice. A lot of work and study went in to that selection. My T-5 begins with a 4.03 first gear and ends up with a .86 fifth speed. If you do the calculations, you'll see the final gear ratios in my first 3 speeds match the original final gear ratios within a hair or so. This means the truck performs in town exactly the same as it did. In my opinion that's important (especially if you live anywhere with hills) unless you enjoy replacing clutches and don't want to haul anything heavier than a 6 pack in a styrofoam cooler. Bottom line is I can still load 800~1000 pounds in the bed and drive off without any problems. Then fourth gear is a 25% reduction in rpm from the original 4.11 rear end and 5th gear takes it down another 14% from that. With the tire size I have at 55 it will be about 2000 rpm and at 60, around 2200. With 5th being so close in ratio to 4th, if I'm driving on the highway in an area with rolling hills and I want higher rpm, I can simply leave it in 4th until things level out more. Honestly I think that is pretty much ideal, especially if you have a well-running engine. It is a fine line. Above 2500 rpm certain inefficiencies start appearing which have been discussed here numerous times.