My brother shoots a Bear Supermag 48 with flemish string I made for him, he has a 29"ish draw I think (I think it's too long for that short of bow but he says it's fine for him).

He put the Bear quiver on it, the one that screws into the bushings on the side, and when he shoots it vibrates a lot! When he shoots with the quiver on, and a few field point tipped arrows in it, the arrows actually rattle out of place! He said it won't do it with broadhead but thats not the point, even with the quiver off it still looked like it vibrated a lot.
Think it could be the brace height? I think I have it at around 7 1/2".
Any help would be great.
Thanks

Bakes

It sounds like his target arrows have much less mass than his hunting arrows, or his arrow nocks are so loose it is almost dry firing. Put a field tip on one of the hunting arrows and see what happens.

Brace heights on those short Bears was pretty high, 8.5"+.  Crank it up and see if it helps.

yep, on a super mag it should be way higher at brace, as Rick said 8.5" +. Get it up there and I bet the vibes go away.

Danny

Is this a new Super Mag with factory installed quiver bushings or a vintage bear with home handyman bushings? In other words, is the quiver on tight or does it have some play?

High brace is always good on a super mag, but your brother says the hunting arrows don't give it the shakes, and if your brace is already 8 1/2", something else is going on.

Cut a couple of small "washers" out of rubber inner-tube and put them between the quiver and the bow.