Burgy
Is this a vacuum shift? Or an electric. Seems kind of new for vacuum. Could be leek if vacuum, at axel/ diaframe. or if elect check shift box on axel, Little moter moves sun gear in and out, but also operates a knif blade switch that sometimes after a time does not let moter compleat the move of the sun gear,the switch also reverses the polarity of the moter to pull the sun gear out back to low gear. OR BAD ELEC SHIFTER SWITCH AT SHIFTER. First things first electric/ OR VACUUM ?
