Try turning the engine to see if the "clutches" are stuck together. The clutches should be loose IE you should be able to move them "fore and aft" just a tiny bit. If not pop them apart with a putty knife or screw driver~~DO NOT FORCE as chipping a disc is not a good thing. Also the reversing band should be loose on the planetary drum.
As far as adjusting follow Edward's tutelage!!
Dave Neptune