The guide rod rear mount can amplify brake pulsations and will neven resonate under drive loading without braking, but if you are pulsing with braking you have a run out or thickness problem with the rotors. A little dirst under a rotor can make a good one do that. Some really poor pads will also do it by glazing the disc (rotor) and causing differeing coefficients of friction as the pads pass from one spot to another.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician