I've investigated all the different kinds of transmissions and overdrive units that I've heard of and that might work in something I build...
So far I've not been tempted in the least to buy any sort of add on overdrive. Just don't think they make sense for me. Don't have any personal experience, but none of them seem all that robust, and I know what the manufactures say, but listen to what people who use them say about them. I'm not implying that they are all bad, just they aren't always as great as they want you to think for every situation.
I do have a friend with a GV unit in a pickup with a Detroit, and it's been replaced a few times, They think it's the Jake brakes that kill it, they didn't know, nor did the manufacturer tell them, but it appears that it won't survive engine braking very hard. I've also heard something about the 4 cylinder Cummins not playing well with them, no hard facts, but worth researching and asking the manufacturer before trying to put one behind a 4BT.
Before I'd buy an overdrive unit I'd swap transmission and or rear axle. Or consider a real auxiliary transmission like a Spicer 5831.
Grigg
