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Brake pedal gives no resistance after bleeding brakes

Question:

After replacing the flexible hoses, calipers, pads and shoes on my car, I bled the brakes and then came to test them. When I push the brake pedal, I feel hardly any resistance until the pedal is about 2 thirds down, after which I can feel normal resistance. What is going on?
Do I need to replace the master cylinder?

Answer:

If the brakes worked somewhat well with a much harder pedal before the brake job, I wouldn't be so quick to condemn the master cylinder. Often times the piston is jammed in the caliper, preventing sufficient travel to push the pads against the rotor. However, because the pedal is traveling too far before any pressure builds, I would definitely suspect air or a leak in the system. If you used a pressurized bleeder, you may not have an air free system now. Since you replaced hoses and calipers, you have to ensure enough fluid is pumped into the system to displace all the air in the hoses and caliper cylinders. Try pumping the pedal through full travel several times while monitoring reservoir level and pedal pressure. (Don't open the reservoir while pumping the pedal.) Try bleeding the system again being careful to ensure the master cylinder reservoir is always close to full. The pressure bleeder should automatically take care of these things, but check to see that it is in fact doing so.




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