Small Engines (Lawn Mowers, etc.): Reverse quit working, directional valves, swash plate

Question
I have a John Deere 1998 F525 kind of a zero turn riding mower, 3 wheels.  400 hours, well maintained.  All of a sudden the reverse quit working on the Hydro static drive.  Going forward works great.  Reverse, there is nothing.  Never had a problem before.  I hope it is just a linkage adjustment some where.

Answer
Either the linkage has come loose or is out of adjustment or one of the directional valves in the hydro-stat is stuck.  You can check the inkage by looking at it and seeing if it's a one-piece or two piece.  What it does is move what's called a swash plate, changing the angle, this is internal.  If it's one piece as most are, then you have an internal problem.  If it's a two-piece as a few are, then maybe the reverse linkage is off or needs to be adjusted.

I think the problem will be that one of the directional valves is stuck.  Depending on the transaxle, this is usually a check ball that opens or closes depending on the angle of the swash plate and the direction of the oil pressure.  This would probably require disassembly although sometimes they work theirselves free.