How do you drive trucks with auxiliary transmissions?

Answer 1

An auxiliary transmission is a second gear box basically all it does is split the gear ratios in the main box so if you have a 5 speed box and a 3 speed aux, it would give you 15 gears with small steps between then - usualy around 250-500 revs different. Depending on load conditions select a suitable main box gear to start (1st 2nd or 3rd) and the lowest gear in the auxiliary known as Underdrive (UD). Nhen change aux box to Drive(D) then go to Overdrive (OD) in aux. Next upchange the main box to the next higher gear allowing the engine revs to drop enough for synchronization, then move the Aux to UD (bringing the revs up a small amount to sychronize that downshif) , into D then OD shift main box . Because you wont have synchromesh the down shifting is generally OD-D-UD then do single downshifts on the main box. It is possible to split downshift however if you are facing uphill you generally lose too much momentum making the shift and as such not really practical. With practices this can be done smoothly and a passenger might think that both shifts are executed simultaniously and not in two steps. Because the gear boxes dont have synchronizers, you can execute these shifts easilly without using the clutch.

Auxuiliary trnasmissions come in 4 speed (quadraplex ), 3 speed (tri-pplex) and 2 speed (duplex). For the quadraplex, you use Low Under Drive (LUD) as a stump puller and split UD-D-OD just like a triplex. Trucks generally have multipseed range change boxes these days 9,13,18 speeds on a single gearshift with air /electric controls to switch between ranges or t split between gears. The days of twin stick are over unless you have an old vehicle.