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  1. #1
    Join Date
    Jun 2017
    Location
    New Zealand
    Posts
    4
    My Cars
    E89 135i (N55), X5 4.8is

    E53 brake bleeding problems

    Hello,


    My X5 4.8is suffered from the "vacuum pump seal failure, oil in brake booster leading to brake booster failure" issue - I changed the booster with a new unit and re-used my Master cylinder. I got everything back together and no matter how much I bleed it (I'd have bled the system 3-4 times over 4-5 days) I can NOT get the pedal to firm up. It feels very, very soft. I do not have a pressure bleeder, so I am using the pedal to the floor method. Here's what I do:


    I have used ISTA-D and done the bleeding with the ABS block as well by cycling the pump - still no go. Pedal soft as hell, goes all the way to the floor.


    - Ask my helper to press pedal 5 times
    - On the 6th time, hold the pedal to the floor
    - Run the "ABS Bleed" procedure in ISTA-D
    - I crack the bleed screw (1/4 turn or so) with clear tubing attached to nipple
    - Close the bleeder screw
    - Ask my helper to release pedal


    I repeated this multiple times per corner until no dirty fluid nor bubbles were coming out. I bled in this pattern: Rear Right, Rear Left, Front Right, Front Left.


    After doing all this I had absolutely NO firmness return to the pedal; So I thought I wrecked the master cylinder and got a new one and changed it out. After bleeding, there is still NO CHANGE in the pedal feel.


    I am out of ideas at this point - I don't believe I have a fluid leak since I'm not losing any fluid (level stable). I am using DOT4 fluid.


    The car is parked on flat ground. I have read that jacking up the rear may help but I can't see this helping - the highest point on the master cyl when the car sits flat is the rear port, so any air should be getting pushed out of that?


    Never done this before - am I doing something wrong here or is something else broken? Car was FINE before I started this (with the exception of a broken brake booster making the pedal super hard).

  2. #2
    Join Date
    May 2019
    Location
    Nevada City CA
    Posts
    1
    My Cars
    2002 BMW 530i
    Im not 100% sure about the fix,but im having the exact same problem with a car in my shop. Booster was contaminated from vacuum pump leaking oil past seals. Pump still produces vacuum at 26 in. Replaced booster and pump etc. Used Snap-on scanner and bled system as required with power bleeder. Pedal is crap. Goes halfway down until it starts to work. If you hold your foot on the pedal with the engine off it feels perfect. Start the car and the pedal is half way and will fall to floor if you keep pressure on it. After talking to just about everyone I know, ive came up with a theory. Theory is that because the booster had a torn diaphragm and was not putting enough pressure on the master, there was a issue with the master as well that was hidden (or happened from all the bleeding). Ill report back tomorrow after I replace the master and see if it fixes it. Im at a total loss otherwise. Apparently there is an internal bypass on the master that can cause the crap pedal and the booster failure just was a shitty coincidence.

  3. #3
    Join Date
    May 2009
    Location
    Greenville, SC USA
    Posts
    2,648
    My Cars
    e39 M5 e39 540i6 e83 e53
    Make sure you are using DOT4 LV (low viscosity) brake fluid.

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