Hi Norm.
Yes I have other Victa self drive mowers and the wheels skid backwards when dragging the mower back, but this
one is just as easy to move backwards as moving it forward.

I was just thinking if the gearbox return spring has broken a coil or lost tension it may not be disengaging properly ,
if the mechanism is a little seized you may be able to lever the gearbox engagement mechanism loose with a screw driver.

I will see if this works on one that has too much drag when moving the mower backwards.

Must be a reason why this one moves backwards easily while others lock up the wheels in reverse.

Cheers
Max.