Rebuilding the Brembo 11mm rear master (F650GS)

Discussion in 'Thumpers' started by atomicalex, Jan 13, 2013.

  1. atomicalex

    atomicalex silly aluminium boxes Super Moderator Supporter

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    Rebuilding the Brembo 11mm master cylinder

    0. Tools required
    Inside circlip pliers
    10mm socket
    5mm hex drive
    2mm long drift (10cm) or 2mm Allen wrench
    Tack hammer
    Long-nose pliers
    Flat-head screwdriver
    Dental picks
    Dremel with small round cutting bit
    One full rebuild kit from Brembo, part number 110.4362.41

    1. Remove the master cylinder from the bike. To do this, remove the bolt holding the brake fluid reservoir and washer with a 10mm socket. Return the bolt and washer to the hole to insure they are not lost. Drain the reservoir and replace the lid and gasket. Release the brake line fitting from the top of the master cylinder and back it out entirely. Remove the two bolts securing the MC to the bike using a 5mm hex drive. Lift the MC away from the bike, clearing the brake line at the top. The push rod will slide out of the rubber boot at the bottom with a slight tug. Return the two hex screws to the bike for safekeeping.

    2. Retire to somewhere warm (or cool...), you might be there for a while. Bring the MC with you. Spread some paper towels or other protection out, and drain the master cylinder fully. Set aside the rebuild kit for later.

    [​IMG]

    3. Carefully examine the MC. Remove the rubber boot by tugging at it gently. To help it, insert a flat screwdriver into the groove at the base of the MC and gently prise the boot away. Looking down the bore of the MC, you will see the piston at the center, a white spacer surrounding the piston, and a circlip holding it all together. The circlip may be rusty, if it is, you have some work on your hands. See below for a good (bad) example of a rusty circlip.

    [​IMG]

    4. Remove the circlip using inside ring removing pliers. If the piston is stuck, use a long 2mm drift or a 2mm Allen wrench to drive it out from the top side. Tap the drift or the Allen key gently with a tack hammer, checking the other end for progress occasionally. When approximately 4mm of piston are exposed, gently grab the piston with long nose pliers and slide it out. This will all require some effort. The spring and spring seat will also come out at this time, or can be shaken out gently. Examine the piston for corrosion and clean it.

    [​IMG]

    [​IMG]

    5. Now for the fun. The white sleeve may not slide out willingly. If it did, you would not likely be attempting this repair. A rather easy way to remove the sleeve is to grind or cut a groove in it. I used a 2mm ball-shaped cutting bit on my Dremel and ground out two channels, one the full length of the sleeve. Using the circlip pliers, twist the sleeve in the MC body and slowly work it out. Another way to remove the sleeve is to turn the bits of a 90° circlip tool to the outside and use it as a puller. In either case, take care not to damage the surface of the bore. It is not a sealing surface, but smooth is very important to the cylinder staying functional for any length of time. After removing the white sleeve, remove the o-ring that is still in the bore.

    [​IMG]

    6. Once the white sleeve is removed, you will have to clean the inside of the outer bore where the sleeve was sitting. If the circlip was rusty, you will likely also find rust inside of the bore. Using Scotchbrite, steel wool, or very fine sandpaper, remove the red rust from the bore. Clean the bore to remove the residue from this round of cleaning.

    [​IMG]

    7. This step is critical to determining whether the MC is going to be repairable for any length of time. After the red rust is removed, use a pick to investigate the condition of the outer bore. If you have tiny fingers, they will work, too. Now, you are looking for corrosion of the aluminium cylinder body. This is the corrosion that is causing the piston to stick, not the red rust. Using a pick, gently flake away any aluminium oxide that has built up in the bore. Under the oxide will be pits. There is no getting around this. Fortunately, these pits do not interfere with the operation of the cylinder if they are properly treated prior to reassembly. This process is slow and time-consuming, but will pay off in the end. When you have removed the fluffy stuff, carefully clean the entire MC and the reservoir and feed line. Blow them out well with clean water and air, and dry thoroughly.

    8. When you have removed the aluminium oxide from the bore, it is time to open up the rebuild kit and start putting things back together. Remove the white sleeve from the kit and test fit it to the bore. It should float smoothly in the bore with only very slight resistance to turning or sliding. This indicates that the bore is free of oxide. Remove the white sleeve, and coat the inside of the bore with Loctite Silver or Heavy Duty (black) antiseize. Do not use copper-based antiseize! This coating should be very very light. Coat the new o-ring with brake assembly grease (HMW polyoxyethylene, supplied in the kit) and insert it into the bore. Insert the white sleeve and twist it gently in the bore. Assemble the spring to its spring seat, and slide the spring into the bore. Coat the piston and seal with brake assembly grease and insert them into the bore. The piston will stick out a bit.

    [​IMG]

    9. To finish the assembly, fit the new circlip to the inside circlip pliers. Secure the master cylinder body and hold the circlip over the piston. Using a suitable drift, inserted through the center of the circlip, depress the piston into the MC, and secure the circlip. Treat the circlip with a drop of wicking grade low-strength threadlocker and, using a pick, draw the threadlocker around the circlip to coat it evenly.

    [​IMG]

    10. Bench bleed the MC and install it to the motorbike, in reverse order of removal. Fully bleed the braking system, including at least one ABS activation in the middle of the process.

    Conclusion: The boot on the MC is poorly designed and encourages water to enter the space within the boot. Basically, the boot should be inserted into the MC, not sitting on the outside. This moisture leads to corrosion of the circlip. However, corrosion of the circlip is not the reason the whole thing fails, it is just part of a chain reaction of fail. Once the iron starts to go, it triggers a galvanic reaction in the aluminium and the aluminium begins to corrode. The problem is that aluminium oxide is fluffy. Very fluffy. And very incompressibly crystalline. This increase in volume puts pressure on the white sleeve and eventually causes the piston to bind.

    My fix: Forget grease. It won't hold up. Use a heavy duty anti-seize product like Loctite Silver or Heavy Duty (black) to fill the void between the sleeve and bore, and then coat the circlip with low-strength (green) wicking threadlocker, which is commonly used as an anti-corrosive coating on automotive fasteners. If you are in Aviation and have access to Alodine 1424 or the like, a coating of this on the inside of the sleeve bore (along with overnight drying) will also go a long way to preventing repeat performances.
    #1
    NahdarVebb and tkach like this.
  2. Appa x4

    Appa x4 Adventurer

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    Thanks for this terrific step by step on rebuilding the master cylinder. I chose to replace it with a new unit on my 98 Funduro. The problem that I now have is that I can't build any pressure in the system to bleed it. I have no clue how to bench bleed. Could you please describe the process. Thanks.
    #2
  3. MiamiPhoto

    MiamiPhoto Been here awhile

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    Thanks soooo much! I am doing this tonight after my kids go to bed. (My rear brake got stuck and all indication points to master cylinder...:))
    #3
  4. atomicalex

    atomicalex silly aluminium boxes Super Moderator Supporter

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    It's been a while since I posted this.

    Appa x4 - bench bleeding is getting the air out of the component prior to installing it into the system.

    Anyway, my rear MC seized up again on two rides. I got the hint this time and attacked it right away. By getting to it before it really went bad, I was able to recover the white sleeve and reuse it after cleaning out the main bore. At this point, I plan to replace the MC body in the near future as this one is heavily corroded now.

    The sleeve, should some enterprising person want to make more of them, is PTFE and 18mm long, 16mm outer diameter, 11mm inner diameter, with (duh) 2.5mm wall thickness. The ends of the bore are turned a bit to allow easier insertion of the piston seal.

    So, have at it, peeps!
    #4
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  5. Don Coyote

    Don Coyote Long timer

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    Hmmm, any enterprising peeps taking up manufacture of the sleeve...?

    Atomicalex, have you tried repacking the grease (did the anti-seize and threadlocker work much better?) in the boot around the MC piston often? I did it a couple of times recently and the last rebuild lasted an extra season, i'm wondering if doing it more frequently like chain lubes could prevent corrosion indefinitely.

    Any idea about ACF-50, would that be appropriate for coating the bore? It supposedly not only prevents corrosion but also renders existing corrosion inert.
    #5
  6. atomicalex

    atomicalex silly aluminium boxes Super Moderator Supporter

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    This time, I used dielectric grease.

    I'll look into the ACF 50. I'm going to run my spare through our plasma coat bath at work and see how that goes.
    #6
  7. atomicalex

    atomicalex silly aluminium boxes Super Moderator Supporter

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    Ok, I looked at that. It would help, but won't be a long term solution. If an annual rebuild is tolerable, though, it should do fine. You would just need to open it up regularly to check. I want a permanent solution, hence trying the TiO2 plasma coat.
    #7
  8. MoDoc

    MoDoc ***oc

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    Do you think the MC's are the same component between the two bikes? I have the G & it just started the sticking (& BTW the ABS lights pops on as well). I'm down for the rebuild if it's really worth the trouble/time.
    #8
  9. Georgi

    Georgi n00b

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    #9
  10. atomicalex

    atomicalex silly aluminium boxes Super Moderator Supporter

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    MoDoc - I believe so. Best to check RealOEM.com.
    #10
  11. atomicalex

    atomicalex silly aluminium boxes Super Moderator Supporter

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    #11
  12. Craigph86

    Craigph86 n00b

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    Thank you for this awesome info. Any advice on replacing the ring around the plastic elbow that connects to the reservoir pipe? That's where my leak is.

    Got the seal kit and whilst following these instructions I managed to destroy the white sleeve! It was pretty much stuck.

    Anyone get around to making the PTFE sleeves by any chance?
    #12
  13. JoeAsheville

    JoeAsheville n00b

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    That PTFE sleeve was a PITA. The best method I found was to dremel a groove in the sleeve almost all the way through, then take an electricians screwdriver (thin) and carefully wedge it between the sleeve and the body of the master. Twisting slightly, I was able to separate the sleeve from the ID of the master. Then, using needle nose pliers and grabbing the small tab I had created, I was able to grip the sleeve tightly and pull it out. Pushing the needle nose down a little, then wedging again slightly, pushing then wedging, I was able to work the pliers further down into the master to grip the sleeve better if all I was able to do was to pull small chunks of the sleeve out...

    The white sleeve is now included in the kits.
    #13
  14. houlster

    houlster Been here awhile Supporter

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    So just curious. I didn't realize these had a sleeve in them. Does that mean you can change the piston size at will just by getting the rebuild kit for 11mm, 13mm or whatever?
    #14
  15. Cal

    Cal Long timer

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    Old thread...I have a rear master cylinder rebuild kit in my tool box that I did not get around to using before I sold the 650, if any one needs it.
    #15
  16. domjames

    domjames n00b

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    Is it a 11mm? where are you located and How much you looking at?
    #16
  17. Cal

    Cal Long timer

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    Sent off to B.C.
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