Front Wheel Vibrations
 

I just helped a friend put in a bearing that had fallen out of his front wheel. I adjusted the cones so the wheel turns freely but there is no side to side play when clamped by the quick release. Now when going downhill the bike vibrates and then starts to buck almost to the point of throwing the rider off. This does NOT happen at slower speeds. Does this have anything to do with the bearings?? Any suggestions for this problem would be great????

How did a bearing 'fall' out of his wheel? It was disassembled?
Anyway, do it again, count the bearings both sides....the axle should have no play before it's clamped by the QR.
See if the rim is warped slightly.

He was disassembling it. Why? I do not know. How do you check for a warped rim, on a trueing stand?? thx for the info.