Model 68 John Deere, As I recall its just a key that drives the rear wheels, Can the wheels be rusted onto the axle? other then that they should just slide off. That model 68 is a old timer and its been some time since I have had the rear wheels off one. As I recall it seems like the differential has a hollow tube to one rear wheel and a solid axle to the other but as I said its been some time back. It has a chain drive that go's from the transmission to the rear axle inside a housing, and that chain can also give problems.