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Thread: Brake Booster Blues

  1. #1
    Join Date
    Jul 2017
    Location
    austin, tx
    Posts
    43
    My Cars
    1979 e21

    Brake Booster Blues

    installed reconditioned booster, and a new mc. worked great for about 20 miles, then got the stiff pedal with lousy braking.

    does anyone have a spare booster that i can try, to diagnose this?

    i'll pay shipping.

  2. #2
    Join Date
    Sep 2007
    Location
    Houston, Tx
    Posts
    1,978
    My Cars
    '78 320i
    Are you certain you seated the MC seal proper on the brake booster?

  3. #3
    Join Date
    Jul 2017
    Location
    austin, tx
    Posts
    43
    My Cars
    1979 e21
    there is an o-ring in there. i don't see how you could improperly seat it. the mc sits tight against the booster when tightened, no gap. i guess i could order another one and try it.

  4. #4
    Join Date
    Nov 2007
    Location
    Sacramento, California
    Posts
    4,704
    My Cars
    1980 BMW 320i E21 M10B18

    Cool

    That could be the brake booster one way check valve has gone kaput--cost a few bucks-test it

    Randy

  5. #5
    Join Date
    Jul 2017
    Location
    austin, tx
    Posts
    43
    My Cars
    1979 e21
    tested it. air cannot be sucked towards booster

  6. #6
    Join Date
    Nov 2007
    Location
    Sacramento, California
    Posts
    4,704
    My Cars
    1980 BMW 320i E21 M10B18

    Cool

    check the hoses going to the brake booster check valve and from, I run a dual brake booster check valve set up, one check valve 1/2 way and one in the brake booster-- I had a problem once of stiff brakes--vacuum leak -hose clamped to throttle body connection was cracked, sliced off the split hose ends back to normal.

    Randy
    Last edited by 320iAman; 01-18-2019 at 05:24 PM.

  7. #7
    Join Date
    Aug 2018
    Location
    Battle Ground, WA
    Posts
    294
    My Cars
    83 e21 82 E23 80 E12
    I have a used booster thats in fair condition and also a booster thats in great condition. Both have what look like new master cylinders too if interested.

  8. #8
    Join Date
    Jul 2017
    Location
    austin, tx
    Posts
    43
    My Cars
    1979 e21
    i'll fuss with it some more

  9. #9
    Join Date
    Dec 2012
    Location
    topanga CA
    Posts
    483
    My Cars
    84 728i,325Ci, 77 R100RS
    [QUOTE=mtbmx;30185574]installed reconditioned booster, and a new mc. worked great for about 20 miles, then got the stiff pedal with lousy braking.

    Is the pedal maybe stiff because the brakes are dragging and everything's hot?

    Are the brakes OK again when cold/pressure bled?

    20 miles is an odd amount of time for a second booster to fail.

  10. #10
    Join Date
    Jul 2017
    Location
    austin, tx
    Posts
    43
    My Cars
    1979 e21
    it rolls easilly. does not feel like they are dragging. bled brakes again, nothing changed. i'll try another mc o-ring and a check valve

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