69chevdump,
Most 2 speed units would be Eaton. If you can move the button, and hear the unit shift, that is good AND bad.
It means the button is functional, the contact switch in the rear end is good, and the shift motor works...that only leaves the hard gears and linkage inside the differential, which would be bad news.
The entire two speed motor and switch can be easily pulled off the rear end, and either taken to a shop that works on medium duty trucks, or dinked with on the bench.
With this assembly removed from the truck, it exposes a small stub shaft with a slot in it. If you jack the rear of the truck up, you can actually shift the mechanism with a large screwdriver and prove that the guts are good.
The most common failure on these bullet proof Eaton's is a bum switch on the shifter, a bum limit switch in the rear end housing, or a bad motor. Any of these problems result in no noise or movement when the button if shifted.
There is a cover on the motor/switch assembly that is bolted to the rear end. If you remove the cover, you can see the limit switch, and with someone in the cab doing the shifting, you should hear the motor, and see the switch actuator move from one contact to the other.
If you actually hear the thing doing something, it sure sounds like it's working. The first thing I would do is verify the gear lube level in the differential, then jack up the rear end and play with the button as you run the truck....see if you can make it shift.
This unit is electric (if it's a Eaton), so don't overlook the fuse, it must have power.
Stuart
