Is it common pratice and necessary to change the dual mass flywheel when changing the clutch, It has started slipping but there is no vibration the car is a a4 b8 2.0 tdi 120bhp that has done 84000 miles cheers
It makes sense to change the flywheel at the same time as the clutch. If you are having a clutch changed at 84K then something is wrong. If the clutch has been slipping the friction face on the DMF will probably have overheated and possibly gone blue. This is not good for a new clutch. With the transmission design in the B8 the DMF has to come out with the clutch as it's part of the clutch module, so there is no extra labour to change it. If the DMF were to fail say at 130K miles then you would end up replacing it and probably doing the clutch again.
It really is a no brainer to replace both.
This is for the A5 but the A4 is exactly the same. Page 30 onwards