On open drive line trucks you can fit a factory overdrive 3-speed transmission or on heavier trucks find an auxiliary transmission out of a tandem-axle truck. A spicer 5831A comes to mind. That gives you 12 forward gears, of which 10 are useful. 6231As can also be used but it's overkill. I suspect that any of these are more prevalent than an overdrive unit for a closed drive line Chevrolet. You might consider converting to an open drive line.


1951 3800 1-ton
"Earning its keep from the get-go"
In the DITY Gallery
1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.