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No I agree that warped rotors will cause the pulsing, all day. It is the other problems she is describing that confueses me..Besides, they were replaced.
Ok, with the brake pedal being hard when the issue starts there are 4 things that could be wrong.
1. brake booster
2. booster push pin , it pushs the master cyl. valve to push fluid pressure to brake
3. master cly valve sticking holding pressure on brakes
4 ABS system.
Has the fluid ever been low in master cyl., or p/s fluid. If so fluid could have leaked from master cyl., into booster that can destroy the booster.
Also if that is happening you will also need a master cyl.
In most cases ( not all ) hard pedal means booster trouble.
check to see if there is vacum to booster and no leaks I wish I could see the truck to check it. it is hard doing this blind over net.
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