sounds like the forward clutch pack on the velvet drive transmission is not engaging which is usually caused by no or real low oil pressure from the pump and or the clutch pack is broken. There is a big (9") o ring on the piston which engages the clutch pack that could have failed, broken oil pump, real low oil level in sump, lots of stuff could have failed. No mater what it is, sounds like it needs to be pulled and rebuilt or replaced. Damper plate usually start making a racket as the springs fail before they go.