1966 F850 dump truck help needed

[Truck Shop]

5 X 3 and two speed drives was a option.

 

[John C.]

The main box was the five speed. You put the main box in gear and can shift it like any Toyota five speed pickup transmission. There is a catch though, the engine doesn't have enough torque range to pull into the next higher gear so they put the aux box in the will allow you to make small speed changes between the big speed changes in the main box. You might start out in 2 on the main box and 1 in the aux when you have a load. You can't make to 3 in the main so you shift to 3 in the aux and then 4 in the aux. Now you can shift to 3 in the main but you have to shift back to 1 in the aux and continue like that up to your desired speed. We called them row boats.

 

[Truck Shop]

Pretty easy rule to follow when learning or not learning how to shift a set of {sticks, Main box, Auxiliary box}

Up shifting-{Don't shift the main box till your done shifting the auxiliary/Brownie}
Down shifting on a grade-same.