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Thread: Diagnosing hard brake feel

  1. #1
    Join Date
    Sep 2007
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    Houston, Tx
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    '78 320i

    Diagnosing hard brake feel

    My brakes need a lot of leg on them to get the car to stop. Brake Booster worked fine prior to my E21 M42 swap, but 12 months later, after install, the PBB seems to have failed? Or maybe I am missing something.

    I did re-use the E30 M42 check valve, the diaphragm seemed healthy. I thought there was a check valve on the e21 PBB, but it just seems to be a plastic elbow (already purchased a replacement). Anything else I can check before I start looking for a new booster?

    Maybe some master cylinder seals or rings I need?

  2. #2
    Join Date
    Mar 2013
    Location
    Santa Rosa, CA
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    1981 320i silver
    sound like it's not getting vacuum. could you have put the check valve in backwards?
    Last edited by okieflats; 07-22-2018 at 03:51 AM.

  3. #3
    Join Date
    Feb 2006
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    westminster, colorado
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    71
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    1982 320i
    Also check and make sure the o ring at the base of the master cylinder is seated in the groove and in good condition, I went through something similar when I replaced my MC

  4. #4
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    Quote Originally Posted by jayona View Post
    Also check and make sure the o ring at the base of the master cylinder is seated in the groove and in good condition, I went through something similar when I replaced my MC
    I think you have the right idea there...

  5. #5
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    It was the master cylinder o-ring. I purchased a new one and never installed it :/

  6. #6
    Join Date
    Feb 2006
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    I did the same, glad it was an easy fix

  7. #7
    Join Date
    Apr 2014
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    DFW TX USA
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    1983 320I, 1986 325E
    Ill have to check this out once my car has a good engine in it. The brake pedal is hard, but I could still lock all 4 up so I didn't investigate too much.

  8. #8
    Join Date
    Sep 2007
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    Quote Originally Posted by jayona View Post
    I did the same, glad it was an easy fix
    Its funny how you have a box of parts and forget what the part is for until you remember why you bought it or what for. Now to figure out what these box of crank bearings were for....


    Quote Originally Posted by Thecatmilton View Post
    Ill have to check this out once my car has a good engine in it. The brake pedal is hard, but I could still lock all 4 up so I didn't investigate too much.
    Thats where I was... it was safe for the surface roads but I wouldnt get on the highway with it.

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