I have a Craftsman 20 HP 42" mower, Automatic Transmission Model #917.27664, Lately it has not wanted to go in reverse. Now the forward is acting up. I have changed the drive belt and purged the unit. What else can I do?

I have a model 917.27660 and have had the same problem. One comerecial repair ashop tried to sell me a new transmission, but I figured it couldn't or shouldn't be that already. I had my local Sears service man come over and the day before I took of the mower and blew out all the linkage around the right side of the tractor. It helped a bit but my forward was very positive and the reverse was very "mushy". When he got here, We looked at all the normal areas and decided to change out all the pulleys. Not only the three that control the belt tension, but the Double engine pulley. It was amazing. The mower performed as if it we new. Between the streching of the belt but also the wearing of the pulleys There wasn't enough friction to power the belt in reverse. I hope this helps. Good luck
gmoose

Thanks, I will give it a try.