Sizer

Mates having a prob with his clutch. Its been replaced a couple of months ago and was working fine.

Now its slipping, the piston in the master cylinder presses on some bar thing but when the clutch starts slipping theres some major slack between the end of the piston and the rod.

Changed the master cylinder for a known working one and it still does it. Tried bleeding it. That sorted it out for a while but then it goes again.

May also be worth mentioning that when bleeding sometimes the pedal hit the floor and stayed there until pulled up by hand. Then when pumped a few times the pedal felt normal, open the nipple to bleed it a few times and alls well then again for no apparent reason the pedal hits the floor...

Vague I know, but any ideas??

911

Sounds familiar!
Try bleeding this way:
Remove slave/remove shaft from slave.
Open bleed a little and push the piston down fully using a small G clanp right to the bottom of it's stroke. Keep it there.
Bleed the system using dot 5 fluid. Get all the old fluid out.
Top up master reservoir to the top.
Refit the slave, the shaft with a dab of grease on it to the clutch arm and when all together (inc the light anti rattle spring) pump up the system with the pedal. About 5 strokes should do it. Top up the fluid.

If that does not fix it, then remove the helper springs off the pedal located under the dash board (big buggers, about a big as Mini valve springs!)

If that does not fix it, check that the 2 engine/box location dowels are in place. Was one left out when the box was changed??
These are most important!

If THAT does not fix it get the box off and check the whole clutch assembly.
Graham