shake problems

[trigo]

my mustang 93 have a rumbler vibration on the rear axle when i release the pedal clutch why?
after 3 passes in a drag racer event i broken my t-5 aluminium bearings reteiner
is a suspension problem?
the last one....i modified my mechanical cam
to accept standard roller tappets the part # is 14005 cam dynamics old cam with a .05 lift of .594 .618 valve lift and a 322 332 advertising duration
i choice roller because lower the duration a reduce the friction and increase the life of the cam
after this modifications i run well my car and sudden i break a aligne tappet reteiner
,again why??????