Left hand or right hand? I have a right handed on my 74 and once in a great whole a hose underneath where the linkage is binds it up and it won't stay or go in reverse.
I have a 6000 series tractor and there are two wires that hang down underneath the tractor that plug into each other. Sometimes weeds or brush will pull them apart and unplug them. When that happens the tractor won't move until you plug them back in again. Then the reverser works fine.