If the rotors are warped, you will get the shudder any time the brake
is applied. Being an econoline, from lots of past experience, I'd be
checking out the front suspension and steering linkage VERY closely.
That vehicle has rubber bushed tie rod ends and other steering
linkages as standard equipment, and if they get worn (not if, but
when) they get really unpredictable and the "death wobble" is a common
result. Replace with Moog instead of OEM parts to solve the problem
more or less for good.
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