Two speed rear ends.

Where you have a gear reduction in the rear axle, these have two ratio's back there. Just shifted by a seperate knob. Usually found on older MD trucks with five speeds or on heavy haul rigs looking for more possible ratios.

 

My KW had 2 sp rears. They were 4:88's and 3:55's. Just flip an air switch on the dash, bump the clutch and you have changed ratios. Great setup for doing heavy haul or when you run on/off road.

 

Roadway had c model ford trucks that had 2 speed rear ends you just split the rear in every gear. And sometimes just left it in the hi range.

 

Some of the 5 & 6 wheeler gas burners not equipped with air brakes had an electric shift. Same little red button, but shifted range electrically instead of air shift. If moisture got in the electric box it wouldn't shift the rear end or it would get stuck in between. A real pain in n the butt.

 

Some had a manual shifter,

but most of you folks wouldn't remember...........

 

I drove several gas and diesel straight trucks that had the 5/2 setup like you mentioned. It basically allowed you to split each gear in the tranny into a high and low version. If you were empty, just leave it in high range and drive it like a 5 speed. If you had a load on, you could split each gear and get 10 speeds out of it. Start in 1L, then shift to 1H, then 2L, then 2H and so on.....

As I recall, to shift "up" you just pulled up on the switch and then clutched like you were shifting - the rear end would go from low to hi range. If you needed to go from hi range to low range you pushed down on the switch and "blipped" the gas pedal - the rear end would switch to lo range.

It worked well in the trucks I drove and was pretty dependable. I seldom carried a lot of weight, so most of the time you could drive it like a 5 speed, but it was nice to be able to drop down "half a gear" if you needed a little extra to keep your speed up on a hill.

 

What most of you all are talking is the "farm truck" 2 speed axle most common on C60 Chevys, Fords, Dodges.
Todays heavy haul trucks most likely have a 2speed axle like mgfg has or they may even go lower like 8:11 & 5:83 for super heavy haul. If you ever see a 2 speed rear end there big, the pumpkin will all most go from frame rail to frame rail. There is a heavy haul company here that has a truck with a 18 speed trans+a 5 speed+a 2 speed axle= 180 gears combos. If you put every thing into low run the RPM's to 2100 its so slow you can get out smoke a whole cig and get back in with out taking a step forward.

 

180 gears I get lost in 10 sometimes forget that