I have a 98 zx2, auto and when I put my foot on the brake pedal to start the car, it pulsates. More frequently it pulsates when I try to stop and the brakes do not hold. I think it could be the porportioning valve or the master cylinder is bad. I have checked the power booster and it still seems to hold vaccuum.
Sounds to me like your rotors or drums are warped. Does your car have 4 wheel discs? Does the steering wheel shake as well? Or do you feel it in the seat of the car? If you don´t feel it in the steering wheel then most likely the rear discs are warped.
You say it pulsates when you push in the brake to start the car???? Well from that info alone, we can count out the rotors as the major prob. Warped rotors are the most common cause of a pulsating pedal, but they can´t make the pedal pulsate if the car isn´t rolling. The initial pulsating is more than likely from the ABS unit. Once you turn the key the servos in the ABS unit enrgize and go though a self test program. While they are going through the self test they tend to hold and realease presure which would cause the pedal to pulsate a bit. If your ABS light goes off within 5-10 secs after you start, you should be ok. Next time you start your car, check to see if the ABS light starts blinking randomly. If it does, it may be outputting an error code and you should take it to the dealer or qualified Ford mechcnic to get it checked out. The ABS could be causing the pulsing while you are driving too. Do you have the stock size tires on your car??? If you put lower profile tires, smaller rims on your car, or even low tire pressure the speed sensor will think you are slowing down faster than you really are, and could kick on the ABS. Another thing is the system may need to be bled. You will want to check the service manual before doing it your self, because some ABS system can hold up to 2000psi in reserve and once you open the bleed screw, it could do some real damage to you or your car. Let me know anyother info you can about this prob and I´ll try to help out asa best as I can.
My GranPrix does diagnostics twice. Once at startup, and then at the first 5mph. For me, that´s when I´m backing out the drive. So as I´m backing up, ABS diagnostic kicks in and bumps the pedal so I always feel like I just ran over something...
The car was just inspected and the rotors and drums are fine. The car doesn´t have ABS but we did pull the fuse to make certain that wasn´t a problem. I have also just replaced a check valve to make sure that it was holding vaccuum and it still pulsates. It pulsates while braking now. I wonder if it might not be the master cylinder is going bad?
Have a different place (like a Sears for 15 bucks) check your rotors.
Pulsating in the pedal is primarily caused by run out in the rotor. Most time turning can fix the run out, sometimes you have to replace the rotor.
More important to runout is what´s causing it. Usually a seized caliper, or the little wire clip that pushes the pads apart are broken.
Also feeling run out on vehicles with disc front/drum rear is usually felt more from the disc.
If a second inspection passes on runout, look into a pressure leak deap in the braking system (like a brake line....the master cylinder usually makes the pedal feel "soft"). Also, I would check the wear and balance on your wheels. Tire wear is a good sign of what´s going wrong, and a bent wheel will sometimes show more during braking.
If its happening when you start the car, I would inspect the actual system.
If its confirmed your car is just possessed and can´t find a thing wrong...look at it this way, DBA rotors and EBC pads with steel braided lines and new fluid is a BIG improvement to any vehicle...so its not a waste of money at all.