I changed out the clutch, slave cylinder,and master cylinder. It goes into gear when engine is off, but wont when engine is on. It grinds when I try to put it into reverse! I hired a guy to fix but obviously doesn't know b/c he can't figure it out either! Please help!! What is the problem???? Any input!!!

 

Probably air in the slave cyl, try continually pumping the pedal and topping off fluid if needed.

Did he cut the bands on slave during/before install? Your not supposed to.