Warped brake drum?

[Thed]

After the brakes have been warmed up and I've been driving for about 25 miles the rear passenger side brake starts to vibrate. There are no other vibrations when I'm driving. What in the world?

 

[Thed]

Bump

 

[94 lngbd]

May be broken brake shoe hardware like a retainer spring,but how do you know its the drum & not the tire out of balance or even loose lug nuts?

 

[martin]

Many years ago I had a drum with a hairline crack in it, very very difficult to see. It caused similar symptoms to yours. If you suspect the drum try exchanging them left with right and right with left and see if the problem transfers to the other side.