I like the idea of an auxiliary between the clutch housing and the main box. That way the auxiliary has to handle only the torque of the engine and not the torque of the transmission in the lower gears. Although I never owned one, I thought the Warn units of the 70's were a good idea, and the few I knew about were tough units. I don't know why the idea never caught on more than it did. As for the Gear Vendors units, I think they are meant for reducing RPM on an empty or lightly loaded vehicle. In direct, I think they are just as tough or probably tougher than the Borg Warner OD. Divorced auxiliary transmissions are not a cheap way of going faster. They require another drive shaft, elaborate linkage and a good strong crossmember on which to mount them. I haven't had an auxiliary transmission in an over the road truck in 40 years. They have their place in heavy haul which I don't do. Even though we grossed over 100,000 lbs. with grain until about 25 years ago when Texas started putting teeth in their load limit laws, I didn't need anything more than a 9 Speed. We now legally gross 84,000 in Texas and I use 10 speeds for the lower gear to untrack in soft sand. I still remember an ad that Cummins engine published in about 1977 which read "either you can get more gears or you can get more torque" when the developed the big cam formula engine. I chose the more torque route with their big cam engines.
