Small Engines (Lawn Mowers, etc.): Issue with changing gears, murray lawn tractor, briggs and stratton

Question
Hi,
I have a 1990 Murray lawn tractor, 12hp Briggs and Stratton, 38" deck.  I have had this mower for about a year and I've been working on it for...about a year, lol.  First off, I know very little about small engines, but I try to fix whatever I can myself.  The problem that is stumping me is that it is EXTREMELY difficult to change gears/speed.  It takes all my might (and I'm a fairly strong woman) to move the shifter, then I have to make sure it is in gear perfectly before the mower will move.  The biggest issue is that it will now not go into reverse.  I push and push but it just will not 'catch'.  Is my tranny bad?  The belts and pulleys all look fine, and when its in gear it rides perfectly.  Any advice would be greatly appreciated!  Thanks!

Answer
Most likely the trans has rust or really old grease in it.

The trans is not a Murray...they do not make transaxles.

Check out this manual and let me know if you have a Peerles and what model you have.  

http://www.wfmfiles.com/download/Tecumseh-Peerless_Motion_Drive_System_-_Transmi(691218).pdf

The model number will be on a plate or sticker on the transaxle.

Will the mower shift easier if the engine is off?
Eric