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Intermittent Brake Booster vac leak, M50 with E21 booster

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    Intermittent Brake Booster vac leak, M50 with E21 booster

    My car is 1989 325i with M50b25 using e21 booster and bmc and non functional ABS and stainless steel brake lines. My pads are worn so time to do the brakes and having intermittent issues so wanted to clarify what to check to get everything refreshed. Recently been having intermittent issues with brake booster. Sometimes at a stop when pedal is depressed I get a vac leak type sound above brake pedal and it gets hard, with associated erratic idle. It also sometimes happens intermittently when driving and depressing brake and if it happens when pressing hard it feels like the car pulls a little to the right. Can the booster leak intermittently and should I check anything else prior to pulling booster to check? Could the pulling to the right be related to booster? I know my rear pads are well worn otherwise everything else in good condition. I'll be replacing pads and rotors and checking and servicing caliper shafts and boots so I assume that would rule out possible seized caliper issues.

    #2
    Yes, the booster can leak intermittently from the pedal side of the booster.

    When you depress the pedal, the push rod is moving through a seal. That can cause intermittent vac leaks as it moves through the seal. If you're hearing a vac leak in the cabin, getting a hard pedal when you do and the erratic idle, I think it's safe to say the booster is toast.
    Current Collection: 1990 325is // 1987 325i Vert // 2003 525i 5spd // 1985 380SL // 1992 Ranger 5spd // 2005 Avalanche // 2024 Honda Grom SP

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      #3
      Yeah that's what I figured. I'm most likely just gonna get the e21 cylinder rebuilt. Looks like IE does rebuilds, anybody know of any other rebuild places? I read about people using a new jetta booster which can be had for $100, and apparently you just have to cut the threaded rod to make it work. Sounds slightly janky and doubt it's better than the E21.

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