John deere 314 mower with hydrostat bangs into forward gear and will not back up at all, why?

Hi,
It would seem that you have wear in the control linkage that does not allow the hydro to engage properly in forward and is beyond the operating range of reverse(which is at best only half the speed of forward. Link to JDParts is:
John Deere - Parts Catalog
Just enter 314 and hit Find to get the 312 and 314.
Picture attached.
Peace,
Clarke