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Thread: Brake Caliper Locked up

  1. #1
    Senior Member red911's Avatar
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    Brake Caliper Locked up

    Hello all,

    Just took the 1967 Coupe out for bedding brakes.

    After two stopping sessions of 5 hard braking from 60 to 20 mph, the rear caliper started to brake the car so much that I had to pull over. The brake pedal was not moving down and it was hard and I could not push it down at all. No movement in the pedal. Blue brake fluid.

    I opened the brake bleeder and pumped the brake pedal twice and the brakes freed up.

    My thoughts:

    1. Air in the system that boiled and kept the system locked up.
    2. Fault in the braking system. (Note: I need to rebleed the brakes)
    3. Your thoughts.

    I have never had this happen. Everything is new. Eric rebuild the calipers, stainless lines, dual master cylinder, Blue fluid.

    Thanks for your thoughts.

    Tom

  2. #2
    Senior Member
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    any leaks of fluid?

    porschegal

  3. #3
    Senior Member M_deJong's Avatar
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    Reads to me like the master cylinder piston got stuck and didn't retract enough to uncover the compensating port.
    Mike de Jong | '71 911T/E 2.4 Tangerine | '74 911S 3.2 Ice Green

  4. #4
    Senior Member 911quest's Avatar
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    I would check the pushrod on the pedal cluster there is a part number difference from a 67 to a 68 that used the dual circuit master cly.
    Tony Proasi

    52 split window coupe

  5. #5
    Did you cut down the pushrod? Did you taper the end of the pushrod properly? Did you establish the 1mm clearance between the MC piston and the pushrod so the piston can fully retract when your foot is off the pedal?
    1966 911 #304065 Irischgruen

  6. #6
    Senior Member red911's Avatar
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    Hello all,

    Progress has been made but not tested as yet.

    I checked the clearance between the rod and the brake cylinder. I have the shorter rod, as I switched from a single to a dual master cylinder. I had mistakenly screwed in the rod about 3/8" too far past the 1 mm clearance.

    There were no fluid leaks and the reservoir is full.

    I have other items to address before I drive the car again, but I will report back on the progress of the brakes hanging up.

    Thanks to all that commented. That is the value of this forum. Folks helping folks.

    Tom

  7. #7
    Senior Member
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    One other cause for locked calipers; probably not your issue because you changed everything but I'll throw it out there anyway. Over time the rubber brake lines can swell and essentially squeeze the bore shut. On pedal application the fluid pressure forces the hose open, but then after the pedal is lifted the hose closes again, trapping the fluid in the caliper and keeping it clamped on the rotor.
    Jeff Jensen

  8. #8
    Senior Member red911's Avatar
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    Ah yes, that has happened to me too. The right front caliper got so hot it set the grease on fire inside the wheel bearings. All due to not changing rubber brake lines every five years.

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