A new clutch would always make the clutch lighter when ddepressing. If clutch is cable driven, ensure it is adjusted correctly in order that the clutch pedal need not be released very high before the gears enagages.
The symptom indicates the clutch is slipping and it could be due to driving fault, quality of parts used, improper clutch adjustment or the flywheel is worn.
Send it back to the guy who did the clutch replacement and get their opinion.
Tuesday, December 11th, 2012 AT 4:51 PM