manual brake shake boogie...

Just got a 66 dart. Dude i bought said he did the brakes. Havent really wrenched into it yet but looks fresh and greased unlike the rest of the car which makes me think he did indeed work on them, but the violent shaking when braking from 40mph+ makes me think he may have just thrown it together, taken dome shortcut, or bolted something together improperly. Brakes feel like thier bled and work great (for man drums) as long as your under 40mph. I know a little creeking is normal as the drums get hot.

What could cause this? I am not the first to assume warped rotors or drums, but thats how you make an *** from U and ME. What else could cause brake shake that behaves at low speed? What could he have done wrong? Can they be seated improperly or could something seemingly unrelated might be displaying itself as a brake shake?

Any feedback appreceated, im just looking for insight, so i dont haft to make every mistake ever made one more time next :violent2: