2008-03-01

Brake pedal needs to be adjusted after master cylinder replacement

After replacing the master cylinder in my sis-in-law car, I found that the braking performance didn't improve much. The pedal still went to the floor and the wheel could not be locked up.

I consulted with my brother who was an actual certified mechanic. He suggested that that the brake pedal free play needed to be adjusted because of depth differences of the piston cap in master cylinders. At first I was skeptical. True, the replacement part was a remanufactured one; but was it really that different than the old one?
I measured and found that the freeplay distance was out of spec: 12.7 mm instead of 5 mm. But what could a 7.7 mm difference do to the braking performance?

After adjusting the freeplay distance, I found that I couldn't floor the pedal anymore. Although the wheels still won't lock up, the brake is now good enough for everyday usage. I attribute the inability of the brake to lock up the wheel to older (weaker) brake hose and moderate glazing on the front rotors and pads.

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