Diesel Powered:
Thanks for posting those videos.. I never got to meet Dr. Bill before cancer caught up with him. Not bad for a dentist who paid his way thru school driving truck.. The video of David was after he got out of a wheel chair for a first diagnosed stroke that turned out to be nerve problems in his neck and when they finished straightening out his face. If you watch their left knee in both videos they very seldom use the clutch except in some of the compound shifts.
Mr Hawes:
The basics are a 4 or 5 speed main transmission with wide ratio gaps between the gears, with a 3 speed auxillary box behind it with an underdrive, direct, and overdrive to split the gaps in the main box into 3 parts.In other words from 3rd in the main and OD in the aux to 4th in the main and UD in the aux was a progressive up shift. Some auxillarys were a 4 speed, with first being a low low (left front) which was only used off road and to start heavy loads. And YES you can still put a 4X4 / 6X6 transfer case behind them. A married box is one where the two trannys are bolted together and a divorced set up is where there are 2 separate boxes with a short drive shaft between them. In Dr. Bill's Mack the aux is the front lever and in David's it is the rear one, it all depends on how the manufacturer sets up the shift towers and linkage, especially in the cabovers. In most conventional cabs the auxillary was the right side lever, although in a lot of Macks it was the left lever sorta up against the seat.
The auxillary shift pattern is UD to the left and back, direct to the right and back, and OD to the right and front. As for the main transmission it depends on if the top gear is direct or overdrive. If it is direct it shifts a normal 4 or 5 speed H pattern. If top gear is an overdrive it uses the inverted H pattern the same as the Auxillary. The old saying to describe the top end was "Both sticks against the dash and both feet flat on the floor!"
Hope this will either clarify 5X3's or confuse you worse.
Brocky