Small Engines (Lawn Mowers, etc.): Transmission stuck in first gear, briggs stratton, change gears

Question
Dear Marc,
  I bought a 2 year old Craftsman 42" Riding Mower,Model 917.256830; Briggs & Stratton 15.5 HP and SPICER transmission.  A tag on back of tranny shows: 142603  then  4360  79
  It is stuck in first gear.  Shifter lever is wobbly. Can move shifter from Reverse position into neutral and into position showing 1st gear, freely with clutch in or out, doesn't matter.  Linkage looks normal. But won't change gears.
  Took transmission out today.  Have to buy star tool to remove nuts that hold top to bottom of case.
  Bought it from a neighbor knowing it would not shift, for $250.  Was told local Sears Service no longer works on mowers.  
  Don't know what I'm looking for.  Any words of guidance at this point?
  Thanks,
  Jess.
P.S. Phoned to have Owner's manual sent. Can't find online any schematic or trouble-shooting site to help.


Answer
It sounds like something (shift fork) is broken inside the transmission because the lever moves but doesn't actuate anything in the transmission.  As for service, you are going to have to scout around to find someone who can work on it.  If it's a Sears mower, they should be able to direct you to an authorized service dealer.  I don't know of any online schematics that could help and I don't know if an owner's manual would have sufficient detail to help.  If you take you time (and digital photos along the way), you could repair it yourself...if you can also find the parts.  Transmission failures are never pretty.  Hope this helps.