Last night we ripped a few acres with my JD 8770 four wheel drive.  Tonight I tried to unhook it from the ripper to pull out a set of wagons that sank in the soft ground and it wouldn't move.  It has the 24 speed transmission.  Everything appears to be shifting correctly, the linkages appear to be moving,  but the tractor won't move or even attempt to move.  It steers fine, but I guess I didn't try raising or lowering the ripper to see if the hydraulic remotes worked.  Is there a torsional dampener that could have let go?  When my Cat 45 dampener let go, it was very noisy but it was pulling a ripper at the time.  The 8770 ran fine when it was parked, and just won't move tonight.  No unusual noises  or anything.  Any ideas?  Hopefully cheap ones!