[Grant Bowker]

C15A case is single speed, C60 two speed.

Parking brake - C15A uses cable to the rear wheels, C60 (S and L are similar) uses a drum on the rear driveshaft actuated by a rod. It is possible to graft the parking brake setup from a C60 onto a C15A case. Early C30 had two speed cases with wheel mounted parking brakes.

Shift linkage - The single speed case uses a lever mounted to the floor to engage the front axle. the two speed case uses an entirely different linkage system to control range, front axle engagement and winch function (if fitted). Actually, there's more than one linkage setup for the 2 speed case. I'm not sure whether all C15A have the crossmember drilled to locate the bracket (both bolts and locating pins) for the shift setup used on the two speed case. The bracket has to be firmly and precisely located as there isn't a lot of adjustment in the 2 speed and PTO linkages (a bit better for the front axle engage). The cab flooor will also need modification as the levers for the cases need different size/shape holes, located differently. Single speed to the right of the case and somewhat slot shaped, two speed to the left and squarer.

In summary, I've seen a two speed case put into a C15A (Cab 11). It took a bit of work but was done. The benefit is that it is better for low speed work. The negative with respect to originality, you have to decide for your truck. I also believe a single speed case could be put into a C60, but why would you want to? I don't think the combination of a heavier truck without the lower gearing available would be good off road, parades, steep hills.

Unless the gears are terminally rusted, they are pretty durable. The bearings to do a rebuild are available (or were when I rebuilt mine). The cases are also pretty solid unless badly abused. Follow the manual and a rebuild isn't too bad. Just be careful on the adjustments of bearing preload and linkage setup (a bit fiddly but not terribly difficult, doesn't need a lot of specialized tooling).