Clutch liling surface getting HARD in goods industrial vehicles 1

[scorpiosandy]

I wantto know about the cause of clutch lining surface getting hard in a commercial vehicle(in goods/haulage & tippers)after running hardly 10000 kms.This problem consequentialy damages the pressurte & face plate in flywheel.Though the material used for lining is asbestoses, which was same as used earlier but problem stsrted recently. Withdrawl mechanism found OK.Clutch cushining springs & hub are in good condition.Clutch systemm we r using is SINGLE PLATE DRY TYPE CLUTCH.No alteration in linkages is done for disengaging clutch.Right now we are simply changing the clutch lining as under warrenty but could not find out the root cause of failure.The surface of clutch lining after failure appers with overheating & thermal spot marks, with burnt smell & seems to be look glazed. kindly help me out to find out the cause of failure. thanks