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Thread: BJ8 brake master cylinder question

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    BJ8 brake master cylinder question

    I am replacing the brake master cylinder, and I ordered a new one, Moss # 581-102. The catalog indicates that this is the one for a BJ8 with the servo.

    When I tried to install it, it seems that the diameter of the new one is too large to fit the hole in the firewall. I checked the diameter of the hole with a digital caliper, and it is 1.325". I have the old master cylinder that I removed some time ago, and across the rubber cover (dust shield?) it measures 1.44" (between 1 and 2 on the photo) I know I took it out, and I assume that it will compress the rubber somewhat to fit the hole.

    However, the new one measures 1.59" at the same point, (between 3 and 4 on the photo) and I don't see how it is going to fit.

    Also, the outside diameter of the shaft on the old one (between 5 and 6 on the photo) is 1.25" and the new one is 1.34" (between 7 and 8 on the photo).

    Did I order the wrong part? I recognize that the old master cylinder may not be the original, although I have owned the car since 1979 and haven't replaced it. Is there some technique that I don't know that would make this fit in the hole in the firewall? I am perplexed. Any suggestions would be appreciated

    .Brake master cylinders old and new ver2.jpg

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    Yoda John Turney's Avatar
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    Re: BJ8 brake master cylinder question

    Based on my brake work recently, send it back, tell them it doesn't fit, and buy either 513-147, the rebuild kit, or 581-100, the TRW brand.
    John, BN4

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    Great Pumpkin Keoke's Avatar
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    Re: BJ8 brake master cylinder question

    A

    Digger:

    Send the old original one to White Post there in Virginia and have it rebuilt
    1966 Daimler V8 Saloon; Safely Fast, Built to Last & and; Smooth as Glass.
    1966 BJ8 [ 2 ] Lil Red & Miss bLU
    1985 XJ6 Saloon
    1948 & 70 Lincoln continentals
    1973 Volvo P1800ES

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    Jedi Knight Rob Glasgow's Avatar
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    Re: BJ8 brake master cylinder question

    Digger, I'm not sure if you are measuring the diameter of the rubber cover between 1 and 2 (also 3and 4) or the actual metal with the rubber removed. In order to install the master cylinder through the firewall, you first have to pull the rubber boot off the cylinder and slide it down the rod. Then insert the rod into the hole in the firewall, push the rubber boot through the hole, bolt the MC to the firewall and then from inside the car, slip the boot back on the lip of the MC. Last step is to attach the rod to the pedal. The MC will not go through the hole with the boot in place.
    Rob Glasgow

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    Re: BJ8 brake master cylinder question

    Rob,

    That works for the old one I took out, but not for the new one. I am going to follow the advice to return the new one and have the old one rebuilt by White Post.


    Thanks for all of the comments.

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    Jedi Knight Rob Glasgow's Avatar
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    Re: BJ8 brake master cylinder question

    Thanks for the clarification. Good luck with the project. I wish the designers had given us a tad more room to access the clutch MC. It's a bear.
    Rob Glasgow

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    Yoda
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    Re: BJ8 brake master cylinder question

    Quote Originally Posted by Rob Glasgow View Post
    Thanks for the clarification. Good luck with the project. I wish the designers had given us a tad more room to access the clutch MC. It's a bear.

    It should be a piece of cake on an English--i.e. RHD--car.

    Edit: Do the RHD cars have the voltage regulator on the port side?

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