Hi, I've got a '94 Toyota Pickup DLX 4x4 that has developed a shimmy in the brakes after having to slam on them in traffic. I want to pull the front rotors and either have them turned or replaced, and was reading in the service manual about measuring the disc run-out before pulling them, and after installing. I've never heard of this before, can anyone explain what "run-out" refers to, and how to measure it?

Thanks!