Front caliper piston leak? - BMW F800 Riders Forum & Registry



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  1. #1
    Culager's Avatar
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    Did some maintenance on front calipers on my 2011 F800R (soap cleaning in hot water, cleaning the pads etc.) and during the process of cleaning the caliper pistons, while pushing them in and out to get them moving properly, I accidentally pushed one piston out too far and the break fluid started to leak. I managed to push it back into the caliper but now every time I work the pistons, that piston comes out of the caliper "wet" of braking fluid. Pistons are in great condition, no oxidation.
    Did I somehow ruin the O ring inside? Or is this just the fluid residue of the leak? What do you guys think and how do I test this to be sure?

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  3. #2
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    you have probably upset one of the seals. I would remove the offending piston, remove the o-rings and replace them to be on the safe side. It's a small cost for the safety of a vital component.
    BMW F800ST, 2010, Black, Fuzeblock, Sat Nav, BMW Tank Bag, Givi Touring Screen, 

  4. #3
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    Quote Originally Posted by DJ123 View Post
    you have probably upset one of the seals. I would remove the offending piston, remove the o-rings and replace them to be on the safe side. It's a small cost for the safety of a vital component.
    Thanks for your advice, I'll do that. I'll try to replace the seals without braking the caliper apart. Found some warnings online about breaking the caliper apart not sealing properly when bolted back. Also couldn't find any info about torque value for that.

    Any advice on where to order the seals?
    Looked on ebay and the only kit I could find i quite expensive ( https://www.ebay.com/itm/BMW-F800-R-...cAAOSw-GNb-wt9 ).

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  6. #4
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    You should be able to do it without splitting the callipers, although it may be a bit fiddly.

    Have you tried your BMW dealer? They may sell the seal kit that you can see at motor works here.
    BMW F800ST, 2010, Black, Fuzeblock, Sat Nav, BMW Tank Bag, Givi Touring Screen, 

  7. #5
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    Going to pay a visit to a local BMW dealer today and see if they sell the kit.
    Forgot to mention, I only tried to push the piston in and out by hand and didn't put brakes together with pads and put them on a rotor. Local car mechanic advised that I should do that and apply the proper pressure to see if it leaks. He also said that break fluid that I see could be the result of a residue fluid from the leak. He said that only when proper pressure is applied I should clearly see if system is leaking and that is highly unlikely that I broke that seal.
    But, knowing myself and how my mind works, I'll probably change the seals anyway no matter the cost. Also found out that my rotors are bellow the BMW specs so I'll have to change both of them. There goes additional $400.

  8. #6
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    I'll keep this thread alive until I solve the problem, I just hate when someone starts the thread and doesn't follow it trough to the end and you never learn what happened.

    Paid a visit to a local BMW dealer and they do not sell seals for my bike. They only sell complete caliper.

    There is one local company that makes seals on CNC machine and if I pull the seals out of the caliper I'll pay them a visit and see what they say. But first I'll test the calipers when I get the chance.

  9. #7
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    if not Motorworks in the link I sent above do post international, so maybe good as a last resort.

    Hopefully that's all the issue is and you don't need to split the callipers.
    BMW F800ST, 2010, Black, Fuzeblock, Sat Nav, BMW Tank Bag, Givi Touring Screen, 

  10. #8
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    A quick follow up:

    Finally found the time to work on my problem. I started with just pushing and pulling the cylinder and every time I pushed it out (using a brake lever) I cleaned it thoroughly to remove every bit of visible brake fluid. I did this procedure maybe 6-7 times. I even managed to spin the cylinder back and forth a bit just to force the seals to "sit" better. After that I put the pads inside and bolted the caliper back on the bike.
    Applied the pressure (hard on a brake leaver) and using a zip tie I blocked the break leaver in that position. I left everything under pressure like that for maybe 5-10 minutes and then I removed the calipers from the bike and inspected everything. Did this procedure maybe 5-6 times and there was no visible leak. Looks like the seals are ok. I'll keep an eye on the caliper and inspect it periodically just to be on the safe side.

    Never the less, I ordered a caliper rebuild kit from a ebay store powerhouse-uk (UK based company, provider of motorcycle brake refurbishment services) if I ever needed repairs. People from this store were very helpful and answered every question that I had. Superb customer service. Highly recommended.

    Regarding the splitting the caliper apart if anyone ever needed to do this, here is the answer that I got from powerhouse-uk:

    And I quote:
    "Do not worry about separating the caliper halves. There is a rubber O ring which seals the fluid passage between the two halves – they never leak from this point. We rebuild many hundreds of these calipers every year, and know that the BMW parts dealers do not understand because they do not have experience rebuilding calipers. The calipers are not prone to distortion and there is no problem with leakage on reassembly. That is false, but it is great propaganda from Brembo to scare people from rebuilding their calipers so they buy new items."

    That is it for now, this is my experience and solution of this problem. I described everything as accurate as I could. Hope this is helpful.

  11. #9
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    Thank you for providing a detailed update. This kind of feedback is what really creates a useful forum.

    Glad you got it sorted.
    Concrete remains undefeated. 

  12. #10
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    Glad that you managed to solve it in the end. Sometimes some perseverance and a bit of investigation is what's needed.
    BMW F800ST, 2010, Black, Fuzeblock, Sat Nav, BMW Tank Bag, Givi Touring Screen, 

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