another diff problem

[losichris]

ok, im on my last legs here with this ball diff, just bought a new rebuilt kit and followed online instructions. tightened it up etc and its smooth, not slipping when holding each outdrive
put it in the car, and it has no drive at all? this is the 3rd diff ive had, they either work for a while, then gradually lose drive, or dont work at all.
i really dont know what else to do, not sure if its me building it, or something else in the gearbox?
but im dangerously close to throwing the whole lot in the bin and going elsewhere!!!

any ideas?