Couple of things to check;
Did you lube the guide pins with silicon grease when you put the calipers back on.
Does the vibration happen on light brake application just before coming to a stop.
If so check your guide pin bushings for excessive play. I recall reading in past forums about the guide pin bushings being the culprit.
It may also be that the piston on one caliper is not working proper. eg. coming out on a angle,(sticking) ?
