help with JCB 5.5hp lawnmower

[pkandtk]

We have a self propelled JCB 5.5hp lawnmower. We have to push it as it does not do it itself. We have taken the plate off where the grass collector is. When we started it up, the lever moves but the wheels do not go round without us having to push it. Can someone please advise on what to do next.
Thanks

 

[Burnerman]

The engine turns a pulley on the top of the back axle - check to see that the belt hasn't snapped or come off the pulleys.
If thats ok, check that a lever, on the rear axle, moves when you pull the 'go' handle in.
If both of these check out, and there is still no self propulsion, its likely to be a rear axle fault.
Hope its the belt!
PS These machines don't like to be turned over - if you want to do that, drain off the oil and fuel first.
John