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  1. #1
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    1 out of 1 members found this post helpful. Yes | No

    1996 840Ci hydraulic-brake fluid leak????Pentosin


    All wanted to share this with you, and thanks to those that have come across this problem before, your comments and guidance’s were unbelievable......

    Last week noticed three distinct leaks under my car while in the garage, a quarter size leak under the driver side at the engine compartment area, another similar size under the driver seat and one last one about a foot back from that one.

    The following day I noticed them becoming larger, bought myself a mirror with an extension arm raised my car on jacks and spent some time looking for it. Had some help starting the engine and pressing the brakes.

    After a while I noticed a drip on the under side of the place where the Brake servo unit and the Master Brake cylinder come together. Read up on the forum and found out there is a square weep hole in the servo and there is an O'ring inside that must has gone bad.


    the "ring part number is BK7272222, paid $0.67 for one at Napa auto stores, also realized the liquid that I was loosing was the Hydraulic Pentosin which one liter is about $37, and bought a small container of brake fluid.

    Now the work begins, get ready for a messy job and if you are 6.4" tall you will have to do some contortion to get underneath the dash to remove the servo unit, and if you use by focal it will be fun....


    I removed the big round container that holds the hydraulic fluid, that allowed me to remove the three bolts that hold the brake master cylinder to the servo, obviously before that you need to disconnect all the tubing and removing the square pressure block will help.

    Once I removed the master cylinder, I went inside under the dash, removed the cover, the plastic vent tube for the AC, and slowly bent over to the companion’s side the bracket that holds the brake switch since I could not remove it easily, oh please remove the connector from the brake switch first. There is a small shaft that holds the brake peddle to the servo unit's shaft and there is a "C clip" retainer you need to remove to be able to move the shaft and release the peddle.


    There are now 4 nuts that hold the servo unit to the firewall, remove and keep them.

    At this point you can go back to the engine and take out the servo to a work bench, on the bottom side you will see a round screw with some one directional slots, you need to remove this while pushing in slowly on the black circular plug at the end of the servo, be careful when you pull this out the plastic pieces will come out pushed by a compressed spring.

    Remove the spring, the washer and replace the O'ring, first lub it with the special hydraulic fluid Pentosin. and proceed to re assemble the unit.


    There is a post of someone being able to do this without removing the servo from the firewall, I tried but could not do it.


    The re-assembly is the reverse, I added the fluids, pumped the brake while leaving one of the top fittings loose to remove any air, and I was ready to go.

    How long did it take? About 5 hours...

    How much did I save? About $1500 bucks....

    What would I do different??

    1) I would have done a better job of catching all the fluid under the car.
    2) Get two containers of Pentosin.

    If you need any further info reach out to me. I have pictures but could not figure out how to post them......

    [email protected]


  2. #2
    rcrad6653
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    Congrats Marcel, for your initiative......

    .... especially as a very recent E31 owner. Bravo indeed. Had we hooked up in phone conversation I could've saved you a bit of work, but that's water under the bridge. Now on to the next few little details: let's see if we can get you better than 3rd place in Concours next time...8^) cheers.

    Randy

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    Brake booster rebuild kits available

    Dang, wish I could have saved you some work by posting this a little earlier, but I was on the road.


    A couple of guys got preliminary bits and pieces of the rebuild kits earlier this year, and the full kits are available now. ALL of the replaceable interior components for the M31 hydraulic brake booster are available, so you can repair a simple leak or restore all the seals in the entire system. I haven't figured out pricing completely, but everything came in fairly reasonable, after a long wait for the teflon seals from Denmark. A simple seal and o-ring will be $6 plus envelope postage for 2 ounces on your SASE. Will publish full kit prices and rebuild instructions shortly; email inquiries welcome in the meantime.



  4. #4
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    Re: Brake booster rebuild kits available

    Hi Folks,

    Been searching the forums for several hours .... I have a 1990 750IL prod date 1/1990, 163,000 mi ..... same hydralics as an E31 ... thus I'm here.

    My usual oil drippings have turned to a puddle .... best estimate is pentosin from the brake booster .....

    my questions ...

    Do you have more info/availability on this rebuild kit?
    What does it include ...is it really just an oring? Am I better off in splurging for the $239 or so for a rebuilt unit from Rock Auto?

    Once at it, can or should I rebuild the master cylinder ...no indication of serious problems.

    Any other hints or a link to a good concise instruction .... it is partially apart ....fighting northeast weather.

    While I'm at it, I'll probably replace Accumulator (brake bomb) ...that has not been functioning well for a couple years ... any hints there ...I'm pretty sure I have the unit that is directly mounted to the pressure switch.... Ready that I can use an oil filter type wrench and just unscrew it ....has anyone else had luck with that.

    Thanks in advance.

  5. #5
    chromeowner
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    Further info on brake booster rebuild kits


  6. #6
    rcrad6653
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    Very nice Bill. Thanks a lot for that.


  7. #7
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    is there already long time experience meanwhile with these seal sets?
    SHOGUN’s TRICKS AND TIPS FOR THE SEVEN SERIES
    http://twrite.org/shogunnew/topmenu.html
    Reply With Quote Reply With Quote 223.132.22.31

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