TRANSBRAKE PROBLEMS ON POWERGLIDE hits reverse??

Got a powerglide that I just got back together after a planetary failure and this started about a week later, When I stage the car and hit the transbrake it engages reverse and rolls back 6" and then stops and its then on the transbrake. Its like it comes out of first and hits reverse only for a sec and then goes back in first. What the Heck is that! Any help is greatly appreciated!! Thanks -Chad

Might need band adjustment

Get the bands ajusted we had the same deal happin to us and cost us a final round

Definatly the band. Its a little loose, trans brakes lock first and reverse together if the band slips it will go backwards. sure thing. the band may also need replacing if tightening dosent help.