Thanks for the info Tony. I am now wondering if these may be grp n shafts as I purchased them off a guy who used to rally a 4x4 cosworth and he had them as unused spares after he sold the car. If this is the case should they not work anyway. It seems to drive O.K. but I get this loud knocking on startup that vibrates right through the seat and I and a few others have had a good look under the car and can't see anything else (exhaust, driveshafts etc ) that is anywhere near close enough to be hitting something when the engine shakes during starting. As it only started happening after changing the front drive shafts they are my prime suspects. David