Strange random brake vibration issue, need ideas.

[foamypirate]

Hey guys,

I've got a strange brake problem with my 87' 1/2 ton. Every once and a while, when I get on the brakes, they will shudder badly. Now, I'm not talking warped rotor shudder, I'm talking, "HOLY CRAP MY TRUCK IS GOING TO RATTLE TO PIECES AND MY FILLINGS ARE FALLING OUT" shudder. The entire truck vibrates very rapidly and violently. It typically happens within the first 3 stops from cold. It will only do this one time, every stop after it does it is fine, nice and smooth, no vibration. It is also typically at low speeds (below 20mph). The intensity of the vibration makes it nearly impossible to determine if it's front/rear or left/right. It's almost like it's maybe locking up a wheel and skidding along.

The part that is making this really hard to trouble shoot, is the irregularity of it. It's only done it maybe 6-8 times in the last 9 months, but it's getting more frequent as of late.

Anyone have any ideas? If you need any more information, I'd be glad to offer it up.