HI, I am a complete novice, is there any chance you could upload pictures, I think I may have the same problem, but would like to get an idea of what I am looking at - or even a step by step photo guide?

You will be able to confirm that you have this problem when you see the tire not spin, but the axle spins when it is in Reverse or 1-6 gears. So the square key needs to "lock" the position of the wheel hub relative to the axle.

This is one solution that really is as easy to do as what Crigby describes above.

Part # 45 is the key stock it goes in the axle then the wheel slides on .
Luck

Thanks mate - I spent some time over the weekend and was able to get it going in all forward gears. I took off all the belts gave it a good all over blow out with an air compressor, removed the wheels, checked the key was in place etc. Im not sure which one of these steps did the trick, but like I said, all forward gears are working like a champ. The only problem I have now is the reverse gear? For some reason I still can't get it to engage in reverse. Any ideas?

part # 45 is the key stock it goes in the axle then the wheel slides on .
Luck

This is fantastic! Thanks for this!