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Thread: Brake -unable to pressurize or bleed '95 K75

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  1. #1
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    Brake -unable to pressurize or bleed '95 K75

    I have a 1995 k75 with 20k miles, with ABS. After noticing a leak from the master cylinder I removed it and honed it out with 0000 steel wool. Installed it and it seemed to be ok. I have been unable to bleed or pressurize the system even when using a Harbour Freight bleeder. At this point I think I've introduced air into the ABS. There is no pressure / resistance on the pedal. I was even thinking of getting rid of the ABS because I know it would probably be easier to get this brake going again. Is the lack of pressure due to a still bad master cylinder ?
    Should I buy a new master cylinder and try that and if that doesn't work then take it to a dealer.
    Any ideas?
    Last edited by deilenberger; 08-31-2013 at 04:46 PM. Reason: added year/model to title

  2. #2
    Benchwrenching PGlaves's Avatar
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    Don't buy anything yet.

    It sounds like air in the system is preventing the master cylinder from priming. Also, check pedal free play to make sure the piston is returning all the way. When I installed new brake lines it took me longer to bleed fill the system than it did to replace the lines. Once you get fluid flowing then just bleed at the modulator first, then bleed at the wheel caliper. Keep adequate fluid in the reservoir so you don't have to move a new bubble all the way through too.

    I favor a one-way check valve on my bleed hose, or a speed bleeder valve on the caliper. Then carefully pump the fluid through.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
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  3. #3
    A bozo on the bus deilenberger's Avatar
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    Hi 48498 (Name?)

    Please see: http://www.bmwmoa.org/forum/showthread.php?46057 - I'm adding this info to your thread title.

    As far as your brakes - when you cleaned the cylinder - did you make sure the hole between the reservoir and the bore was clean? It isn't unknown for these go gum up - and if so, no fluid is going to get into the system. The condition of the brake hoses is also suspect at 18 years.. they've been known to collapse internally and look just fine on the exterior. Usually this failure allows fluid into the system, but doesn't allow for pressure relief when you release the brake, leading to dragging brakes. I believe Paul G has an article in an upcoming MOA Bench-Wrenching article all about brake lines.

    Also - did you replace the master cylinder piston/seals? Or just clean them up? 18 year old seals have a fair chance of being perished... As far as your question on buying a new cylinder - my experience has been about 50/50 with trying to rebuild master cylinders. Often when they fail - the bore has some corrosion in it down at the far end due to water buildup in the brake fluid. No amount of honing is going to fix this. Given those odds - and the PITA that a rebuild involves - if it's economically practical it would be a new cylinder for me.

    And don't eliminate the ABS. Have you bled the ABS modulator? If there is air in it - once you get the fluid flowing it should bleed just fine.

    A caution on bleeding - remember the corrosion in the bottom of the cylinder - often people bleeding the brakes will take a full stroke on the pump stroke of bleeding. This makes the piston go into areas that it has never been in, and the corrosion or pitting will damage the seals. Trick here - tape a block of wood about 1" thick to the lever or the grip (whatever works for you) to keep from going too deep on the in-stroke. That's assuming it's the front circuit we're talking about. If it's the rear - just be REAL careful not to fully depress the pedal.
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  4. #4
    Registered User leftturn's Avatar
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    A caution on bleeding - remember the corrosion in the bottom of the cylinder - often people bleeding the brakes will take a full stroke on the pump stroke of bleeding. This makes the piston go into areas that it has never been in, and the corrosion or pitting will damage the seals

    I have never heard of that but it makes good sense..Always good to read here..

  5. #5
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    Brake 1995 K75

    I removed the dust cover from the rear master cylinder and discovered that the piston was stuck deep in the bore. I have to disassemble and determine the damage. I am now leaning towards buying a new master cylinder, a reservoir hose and clamps for the hose.
    I probably caused this by depressing the pedal causing the piston to go too far into the bore.
    I'm thinking of buying the master cylinder at boneyard.
    Where can I get the reservoir hose and clamps?
    What size clamps, FI type?
    Thank you all for all the info. I only wished I would have asked before venturing out on this task.
    I welcome any new thoughts on this matter.
    Bill

  6. #6
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    1995 K75 Rear Brake

    I installed the rear master cylinder, new reservoir hose and new clamps. I used my Harbour Freight pump bleeder. I now have a soft pedal. I've heard it's impossible, on an ABS system, to get a firm pedal without taking it to a Dealer. Is that true? Where do I go from here. I have a syringe, can I reverse bleed? And if I can ,do I start at the ABS MODULATOR first and then the rear caliper? I also have but have not installed yet, Speed Bleeders.

    How do you adjust the adjuster in the rear master cylinder?
    Bill
    Last edited by 48498; 09-08-2013 at 04:15 AM.

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