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Symptoms of a bad brake booster?

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    Symptoms of a bad brake booster?

    My brakes have a split second delay when first stepping on them. They don't feel spongy but when i first step on them the brake pedal wont depress right way it feels hard at first like something is clogged in the line or something.

    So far I've tried,

    New brakes lines
    New pads/rotors
    Rebuild the calipers
    Different MC from junkyard
    TWO different brake boosters
    Different ABS pump


    NONE of these has made a difference

    anyone?
    Last edited by Highway1; 09-09-2010, 11:28 AM. Reason: Updated troubleshooting

    #2
    A hard pedal is almost always a failing or failed booster. In this case it sounds like it might be the vacuum valve in the booster. If you get a used booster, check the booster for oil or brake fluid. Either of those in the booster will cause the diaphragm to fail. If you get a new booster, use a new master cylinder.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

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      #3
      thanks, I guess ill try and find an e21 booster or some sort to make things easier in the future.

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        #4
        ok so i put an e21 booster in today and the problem is still there. The pedal feels solid but there still is hesitation when I first step on the brakes. could it be the abs unit?

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          #5
          Got one for sale with the input shaft already modified.
          Attached Files

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            #6
            thanks but if you read my post above yours i have already put one in. does anyone have an idea why my brakes are so unresponsive? or should i replace everything else.
            Last edited by Highway1; 08-09-2010, 11:43 AM.

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              #7
              check for air in the system and rebleed again, make sure the calipers are not sticking

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                #8
                thanks but there no air in the system for sure. and they are not sticking. i bled the brakes four times and the pedal feels SOLID with very short travel but my brakes just don't grab at all and i have to push hard to stop fast. i guess i'll just have to try a different MC
                Last edited by Highway1; 08-09-2010, 09:12 PM.

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                  #9
                  How old are the calipers? I've had the same problem for a while even with a new MC, booster. I rebuilt a whole set of calipers and put them on and what a diff it makes. Stops like a new car.

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                    #10
                    Originally posted by Highway1 View Post
                    thanks but there no air in the system for sure. and they are not sticking. i bled the brakes four times and the pedal feels SOLID with very short travel but my brakes just don't grab at all and i have to push hard to stop fast. i guess i'll just have to try a different MC
                    Higher than normal pedal pressure can also be the result of insufficient vacuum to the booster. That can result from intake leaks or a problem with the check valve or booster hose.
                    The car makes it possible, but the driver makes it happen.
                    Jim Levie, Huntsville, AL

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                      #11
                      Calipers were rebuilt last week

                      I was thinking maybe it was vacuum too but then i talked to someone who said it probably wasn't because it feels the same at all engine speeds. I can downshift into 6K rpm and the brakes feels the same as when I'm idling.

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                        #12
                        i just replaced the MC and no difference. I fucking hate my life

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                          #13
                          When you push on the brake does it move about an inch or two then you have to push hard or is it hard right away?

                          If it moves then is hard your brake booster is not operating correctly!
                          1986 RED ROSE (325es)

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                            #14
                            It's hard right way and then i can feel the pedal depress. Maybe this is just the way e30's are.

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                              #15
                              Hard at first but then spongy?
                              Mtech1 v8 build thread - https://www.r3vlimited.com/board/sho...d.php?t=413205



                              OEM v8 manual chip or dme - https://www.r3vlimited.com/board/sho....php?p=4938827

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