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Help - Brake master cylinder problem ?

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  • Help - Brake master cylinder problem ?

    Hi folks,

    hoping someone can give me some advice....

    my NM Pajero (2002 Exceed, ABS etc) suddenly developed a braking problem when I was away on holidays over xmas. Now I'm no mechanic, which will no doubt become obvious, but I'm hoping someone may have an idea of what the problem could be.

    The problem started one morning when I went to go into town to get some supplies (which is over a pretty rough dirt track). The first time I hit the brakes, when I released the brake pedal it made a very strange scraping/vibrating sound. Further investigation identified that the sound is coming from the black dome shapped 'object' on the side of the hydraulic brake booster, and it shakes when the sound is made. The sound happens every time you release the brakes. Further, and more disconcertingly, you can with a constant fairly heavy pressure get the brake pedal to the floor! (takes a few seconds though). Apart from that the brakes actually feel and work OK, and I made it home!

    There are no dash lights showing any problems, although you can get the the ABS light to come on when you push the pedal to the floor, and it goes out again when you release the pedal. I assume this is an oil pressure problem ?

    The oil level in the braking system is OK, and it hasn't lost any oil.

    My guess at the moment is that maybe a small amount of oil is leaking past the piston when you press on the brakes? or perhaps it is a problem with the hydraulic pump?

    Anyone have any suggestions ? I took the car to a couple of mechanics between xmas and New Year in Ulladulla (south of Sydney) but neither had much idea. One suggested the whole brake unit would have to be replaced! $$$$$

    What I need to decide is whether I should wait for my mechanic who is back at work next week to take a look (although he is not a Mitsu expert), or take my car to a Mitsu dealer (which I have never done before, for any vehicle). I'm just not sure how technical this problem will be, and if it's something only Mitsu will be able to diagnose. Hopefully it won't be a case of just replacing the whole unit. Fortunately I don't need to drive the car for the next couple of weeks.

    thanks in advance,

  • #2
    Pretty common fault on the NM Pajero with ABS; accumulator diaphragm in brake booster manufacturing fault which causes loss of power assistance in the brakes.There was either a recall or a campaign no for it. Check with a dealer, and if he claims no knowledge check with another.
    Last edited by Pickle; 01-01-08, 11:41 AM. Reason: My spelling sucks!
    NX Pampas Cat GLS MY16
    Member 1228 Pajero Club


    • #3
      Thanks Dave.
      I've checked that out, there was a recall, but it related to earlier NM models; mine's a 2002, and I've checked my VIN against the recall.
      Different symptom as well.


      • #4
        No one has any suggestions then on what the cause might be?

        And can anyone tell me what the 'black' unit on the side of the braking system is?
        Attached Files


        • #5
          That is the brake booster accumulator that Dave talked about. Still sounds like it's faulty to me.
          Cheers, John.
          LC200 V8 goodness

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          • #6
            it will be that accumulator without a question at all


            • #7
              Thanks guys appreciate the feedback. My mechanic is taking a look tomorrow.


              • #8
                Well my mechanic has spent a couple of hours on the problem and doesn't know what the problem is.... yet. He thinks the brake booster accumulator is OK and that the problem (vibration) is coming from elsewhere, it just makes the accumulator shake, and you can in fact feel it through the break pedal as well.

                The ABS sensors all check out OK, the ABS systems works OK, the brakes work OK and the pedal can't be pushed to the floor; he connected his computer up to the ECU, and everything checks out OK. He thinks at the moment that perhaps the ABS pump is increasing the pressure too much, and that is causing a pressure release somewhere, or maybe another valve or solenoid somewhere is fluttering causing the vibration. Anyway he has gone away to study the workshop manual and think about it.

                Just wondering if anyone has any other suggestions ?


                • #9
                  Yes, another suggestion is to visit your closest Mitsubishi dealer so they can diagnose the problem.
                  I'm pretty sure the accumulator is the problem!


                  • #10
                    We'll I've taken the Paj to a Mitsu dealer, and they aren't sure what the problem is, but they suspect (hope) it will be the accumulator, so after waiting a week for the part they are going to change it and I'm $500 poorer. Lets hope that fixes it.

                    If it doesn't fix it then the whole brake unit will have to be replaced $$$. Quote for this was $3080 at one dealer and $2317 at another (part only) - go figure.

                    As my mechanic found out after many phone calls these units cannot be serviced, for legal and ADR reasons apparently - all a bit vague though.


                    • #11
                      If you just get the " chirp chirp" noise while braking... it will be the accumulator that's at fault... if you get fault codes in the ABS system, " motor fail " and so on with the ABS light on.. then you'd be looking at a fault with the HBB.

                      A head honcho at Mitsubishi told me once you could get parts for the HBB separately... but I'm yet to find any dealer who can supply parts alone, and not the complete unit itself for 2 grand plus!

                      I've pulled one apart myself once, and goodluck to anyone who could rebuild a faulty unit.


                      • #12
                        Well it's now fixed and thankfully it was only the accumulator so I'm only $550 poorer.


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