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Hard brake pedal with limited actual braking! 1800 1970

posted by  Whale on  Thu Jan 6 19:42 CST 2022
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last visit: Fri Jun 14 19:52 CST 2013
[RELATED]

Immediately after replacing my defective master cylinder and bleeding the brakes, I ended up with a hard pedal about half way depressed but Limited braking effect! I doubt it is the booster, since it was working fine prior to replacing the master cylinder. Could the issue be related to the fender mounted small brass electric powered slider valve (Brake System Warning Valve) attached to the hydraulic lines just beneath the brake master cylinder? I had disconnected its one wire prior to bleeding, as directed in the shop manual and then reconnected after. Yes, I bench bled the master prior to installing and the reservoirs are full Presently, the Brake Warning Light is illuminated and the car is not safe to drive in traffic. Hopefully, someone has an solution.








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    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

    It's Obviously the Master Cylinder.

    One of the seals is wrong & if you have a keen eye you will see the fluid level drop in one side & climb in the other.

    Your buying junk assembled by Chinese people on a cup of rice per day, you have to expect this type of thing.

    The emergency switch won't to it, but yeah, you usually have to reset it. I bleed without it in because it can leak too, but it won't fail.



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      posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

      Before condemning the brake master, test it by installing plugs in both ports and if you have a hard high pedal, it's not the brake master.

      BTW, last weekend I disassembled and inspected the exact same brake junction with warning valve and the internal components can not block the ports inside the junction.

      The reason for removing the warning switch is to prevent damage to the plastic tip of the switch which can be shorten each time the internal parts of the junction slide back and forth.

      --
      Eric
      Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
      Torrance, CA 90502
      hiperformanceautoservice.com or oldvolvosonly.com



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        posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

        Planetman: ......I disassembled and inspected the exact same brake junction with warning valve and the internal components can not block the ports inside the junction.

        Whale: .....as I removed the Brake Warning Switch, the hard pedal released and I was able to bleed all of the brakes. Replaced the switch upon completion and now my brakes function normally with the dashboard brake warning light extinguished.....


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          posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

          I can't explain what happened in this circumstance. As I said before, there is no way under normal circumstances that the ports for each brake circuit inside the warning valve can be blocked by the moving parts that are inside the warning valve.

          We've had to replace quite a few of the warning switches because someone didn't remove the switch before bleeding the brakes. But none of those cars came to us with issues traceable back to the warning valve. In most cases, the damaged switches had to be replaced so the light on the dash wouldn't stay on.

          All I can think of is maybe the pistons inside the warning valve were stuck to the point where the tip of the switch provided enough resistance so that the pistons wouldn't move and maybe that trapped some air inside. But there should have been more than plenty of hydraulic pressure to move the pistons during normal bleeding as this is exactly what damages the tip of the switch. Maybe he didn't press down hard enough on the brake pedal while bleeding the brakes the 1st time.

          --
          Eric
          Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
          Torrance, CA 90502
          hiperformanceautoservice.com or oldvolvosonly.com



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            posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

            “…. As I said before, there is no way under normal circumstances that the ports for each brake circuit inside the warning valve can be blocked by the moving parts that are inside…”

            If, by design, that shuttle valve WERE to close off the leaking circuit then it would, in effect, dead head that circuit about 6 inches from the master cylinder. That blockage would prohibit the driver from being able to apply much brake pedal pressure to EITHER circuit, even the good circuit. That means little or no braking. It’s hard for me to believe the switch block would be designed that way.



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    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

    Did this problem start immediately after you changed the master or did the brakes work properly and then the problem occurred?


    Do you hear a vacuum leak or a hissing sound when the brakes are applied with the engine running?


    --
    Eric
    Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
    Torrance, CA 90502
    hiperformanceautoservice.com or oldvolvosonly.com



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      posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

      Yes, the problem occurred as soon as I completed bleeding the brakes and ended up with the half way down hard pedal. No, their isn't a vacuum leak or hissing with the engine running. After reading the manual it hints that it might be the Brake System Warning Valve is out of position and needs to be reset and system bled again. I'll give it try tomorrow.


      Checking my shop manual gave me a clue as per this description: Brake System Warning Valve - The valve is centered by hydraulic pressure from the primary circuit on one side and the secondary circuit on the other. When a hydraulic imbalance exists, such as a leak in one of the calipers, the valve will move off-center. Sometimes, the valve will activate the brake warning light when the system is bled. When this happens, the valve has to be reset.
      Valve Resetting - Disconnect the plug contact and screw out the warning switch so that the pistons inside the valve may return to their normal position. After doing this the system must be bled. Screw the warning switchback in and torque to 14ft lbs. Reconnect the plug contact.


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        posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

        Yes, you have to remove the Brake System Warning Valve before bleeding , if you don’t it could be stuck in a position that prevents proper bleeding. When you have bled the brakes successfully you can reinstall it.



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          posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

          Did what C1800 described and as soon as I removed the Brake Warning Switch, the hard pedal released and I was able to bleed all of the brakes. Replaced the switch upon completion and now my brakes function normally with the dashboard brake warning light extinguished. The forum always has a solution!



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