Diff probelms - odd clunking, sounds like backlash?? HELP!!!

[mycool]

I fitted a 2nd hand Torsen the other week that I bought from the for sale thread on MX5Nutz and since fitting have had a knocking/clunking noise whenever I go on/off throttle when in gear. It sounds like excessive play in the drivetrain.

I properly adjusted the PPF, checked the propshaft joints (nice and tight) and the halfshafts (minimal movement) so its all pointing towards the diff which intuitvely makes sense as thats the only part that has been changed.

I can hold the two halfshafts and rotate about 10°-15° and feel lash within the diff. I dont think it is crown and pinion though so it suggests it is the helical gears.

If I release the clutch quickly with the rear in the air I can hear the lash rattle up and back down the driveline.It doesn't make the noise when I hold constant thottle/torque when driving, or if I do the same and turn - only when on/off throttle or if the torque through the driveline changes - i.e. when going over bumps.

Any thoughts and i'm assuming a torsen should be quiet with no clonks (i know that some plate LSDs clatter/shudder a bit as they lock up).

All help and advice greatly recieved as i'm scared to drive it too much in case I ruin the diff and want to eliminate as many things as possible before going to the considerable hassle, expense and lack of car for a while if having to remove the diff again to send it away.

Many thanks

[mycool]

Forgot to add I have come across a bit in the mx5 workshop manual that says to mark the propshaft before removing it from the diff flange so it can be reinstalled "correctly".

Obviously this is impossible when fitting a new / replacement diff so how can I tell if I have done so as i wasn't aware the prop to diff flange had a "correct" orientation?

Pretty sure its not the cause of my problem but would be good to eliminate another area.

Thanks

[Bbthree]

I have the same problem. Ive fitted a performance clutch as i intend to turbo the engine.
Briefly:

-U-joints are fine
-Exhaust has no rattle and its clearly not an exhaust noise
-front engine mounts are fine
-diff is welded, has been rebuilt to set minimal backlash and has new poly bush mounts
-PPF is set at the exact height however I'm amused that you are meant to be able to get this "to the mm" when the rails are covered in OEM stone chip of varying thickness
-clutch pedal and slave cylinder is set properly
-clutch plate was torqued and installed to spec
-throwout bearing is new, pilot bearing is fine
-flywheel was ok before clutch change
-two gearboxes have been tried and exactly the same clanking occurs when clutch is engaged or accelerator is blipped

Totally irritated with this now. Ive been told 'they do that mate' when you put a high rated clutch in.

Im not really able to accept that.

Any ideas?

Mx5 mk2.5 1.8 vvt 16 valve