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Thread: X3 Please help with locking brakes

  1. #1
    Join Date
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    X3 Please help with locking brakes

    Hi guys, I'm hoping someone here can point me in the right direction. I have 2004 X3 3.0. My brakes start locking up so bad I can't even move after a little while of driving. This has been going on for 2 months now and I've had two different shops and 4 different mechanics look at it. We've replaced the master cylinder twice, the booster once, the hydraulic pump unit twice, and the control module once, and none of that has made a difference. Specifically what it does:

    If I drive a lot where I don't have to brake much (not many intersections) there usually isn't a problem. If I drive right through town where I'm braking frequently, once the brakes get hot they slowly start to grab and just slow the car down while I'm driving and will eventually lock up completely and I can't even move the car. Once it sits for an hour or so the brakes are back to normal until I start driving and braking again.

    The calipers have been inspected and the pistons and guide pins appear to be functioning normally, at least on inspection. The rotors I can feel are warped when I drive a low speeds.
    -Chris
    My e30 build thread/color change here

  2. #2
    Join Date
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    1992 BMW 850i 4spd

    Please help with locking brakes

    Try replacing the rubber brake lines. They can fall apart from the inside and become blocked to a point of not allowing oil to return from the caliper easily.

    On a 14 y/o car, it is a good idea anyway.

  3. #3
    The symptoms are pointing to the calipers locking up. The master cylinder should have been left alone.

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  4. #4
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    When the brakes were locked up the lines were pulled from the master cylinder and pressure was immediately released and the caliper pistons were able to be compressed. That's what pointed us to the master in the first place.

    Would the rubber lines be affected by heat? I can lightly brake or even pump the brakes all day and not have a problem, but after a lot of braking and heat is when they lock up. Perhaps I'll change them out anyway, as it wasn't done yet.
    -Chris
    My e30 build thread/color change here

  5. #5
    This.
    Yes, heat and 14 year old brake fluid. Did they flush the system? The BMW uses a higher heat brake fluid, dot 4. Many diy jobs or jiffy lubes won't even have it. Replacing the lines, unless you had it since new and know it's maintenance hx, is a good idea. Good luck.

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  6. #6
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    Yes, the system has been flushed and bled about 6 times in the last 2 months while we've been working on this. We're using dot 4.

    I'll order the lines and report back once they're replaced. Thanks for the help guys!
    -Chris
    My e30 build thread/color change here

  7. #7
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    You need to get to lock on the rack,then find out which wheel them undos brake line at the caliper and see if it releases

  8. #8
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    We're going to check that, check the travel of the rod in the booster, and hopefully have the new brake lines, pads, and rotors on tomorrow. I'll report back with my findings.
    -Chris
    My e30 build thread/color change here

  9. #9
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    We replaced the brake lines, rotors, and pads. I took it on a nice drive and didn't seem to act up. I'll drive it a couple days and see how it does. The calipers seemed fine. The pistons moved easily and they glide pretty nice on the guide pins. I'll report back in a couple days.
    -Chris
    My e30 build thread/color change here

  10. #10
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    Back to square one. The car was fine yesterday but when I went to lunch today the brakes locked up again and pedal got rock hard. All four brakes were very hot when I stopped. When we replaced the booster we used a reman one. Could the booster be causing this? I can't see all four calipers seizing up at exactly the same time.

  11. #11
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    Breakthrough! So we put it in the air and all four wheels were locked. We unplugged the ABS module first, disconnected the vacuum line from the booster second, and still locked up. We then pulled the master off the booster, and BAM! Brakes released. We must either have a mis-packaged booster or it was installed incorrectly and the rod damaged, but it almost seems like the rod is too long...

    I believe TRW is the OEM manufacturer for these, right? Would I be safe ordering a TRW and saving a couple hundred over genuine BMW, or should I just get the BMW one? Apparently the reman one they installed is a Cardone from Autozone.
    -Chris
    My e30 build thread/color change here

  12. #12
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    TRW is the OES for the booster/master assembly. If it were me, I'd buy the ZF/TRW part.

  13. #13
    Join Date
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    So we got the new TRW booster and pulled the old one off the car, and the rod is about 3/4 inch longer on the reman one we used originally than on the new one. I think we have our culprit! What's odd is the remain one is stamped TRW on the back, but has the wrong rod in it... Strange.

    We're bleeding the brakes today so I'll drive it over the weekend and see how it does.
    -Chris
    My e30 build thread/color change here

  14. #14
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    Seems like the problem is fixed. I haven't had anymore issues since installing the new booster.
    -Chris
    My e30 build thread/color change here

  15. #15
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    2010 X3
    Woohoo! Congrats and thanks for sharing!

  16. #16
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    Jan 2024
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    Camden south carolina
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    2014 Bmw x3

    2014 x3 brakes lock up

    Quote Originally Posted by heifetz17 View Post
    Seems like the problem is fixed. I haven't had anymore issues since installing the new booster.
    As stated while driving sometimes the brakes apply and slow car down. If you tap the brakes they release .when we come to a stop we push the pedal all the way down and then we really don’t have this problem. Independent dealer said calipers. We have replaced pads and rotors and brake lines , flushed the system any help would be appreciated hate throwing parts at it.

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