it seems that i have a vibration that i feel in my steering wheel-BUT-it only seems to occur at 60 -65 mph.what could this be?drive shaft,wheels,axles,flex disc(what the hell is a flex disc,anyways!?)any ideas on how i can check or narrow it down?
thanks!

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'95 s500 (bought for wife but can't bear to share!!!) 125kms
'92 legend 180kms
'88 tbirdturbo(fantastic car-only regular maint.)120kms
'87 mustang gt(gone)
'86 tbirdturbo(gone)
'85 mustang gt(gone-but not forgotten)