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  1. #1
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    Shimano Ultegra RS785 caliper leaking oil due to heat

    I was on a group gravel/mixed terrain ride the other day. We ended up going down a really steep descent where there was lots of sustained braking. I heard my front brake squealing quite a bit. At the bottom I squeezed my brake and saw fluid come out of the bottom of the caliper near the blowoff port. This was an RS685/RS785 setup with an Avid G2CS 160mm rotor.

    1 - Is the little valve where the fluid came out on the bottom (the dust seal got blown off and lost) supposed to act this way in case of heat buildup?
    2 - Was it likely that fluid got on my pads and I need to replace them? Braking afterwards felt okay once things cooled down but fairly squeaky. Is there anything else that needs to be replaced?
    3 - Is this something to be concerned about in the long term? I.e. if the descent was longer could I have lost all braking power?
    4 - In situations where braking is the only option is there something I can do to prevent this in the future?

  2. #2
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    Quote Originally Posted by alxrmrs View Post
    I was on a group gravel/mixed terrain ride the other day. We ended up going down a really steep descent where there was lots of sustained braking. I heard my front brake squealing quite a bit. At the bottom I squeezed my brake and saw fluid come out of the bottom of the caliper near the blowoff port. This was an RS685/RS785 setup with an Avid G2CS 160mm rotor.

    1 - Is the little valve where the fluid came out on the bottom (the dust seal got blown off and lost) supposed to act this way in case of heat buildup?
    No. That's not a blow off port. It for bleeding the brakes. It should never leak fluid.


    2 - Was it likely that fluid got on my pads and I need to replace them? Braking afterwards felt okay once things cooled down but fairly squeaky. Is there anything else that needs to be replaced?
    New pads for sure. They're like sponges and will always have brake fluid on them.


    4 - In situations where braking is the only option is there something I can do to prevent this in the future?
    If fluid was coming out of the bleed nipple, something is seriously wrong! Don't ride it until you figure out the problem.
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    Quote Originally Posted by tlg View Post
    No. That's not a blow off port. It for bleeding the brakes. It should never leak fluid.
    Oh right I did use that to bleed it. Lapse of memory there because with these new calipers the bleed port is distinctive from the screw you have to turn to "open" up the system for bleeding. Is it possible that I blew out some seal in there?

  4. #4
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    Lot's of things are possible. Maybe the seal didn't get put back in when you bled them?

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    Quote Originally Posted by alxrmrs View Post
    2 - Was it likely that fluid got on my pads and I need to replace them? Braking afterwards felt okay once things cooled down but fairly squeaky. Is there anything else that needs to be replaced?
    When I get oil on my pads or other residue, I just burn it off with a butane torch. Squeaking goes away!

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    Quote Originally Posted by Migen21 View Post
    Lot's of things are possible. Maybe the seal didn't get put back in when you bled them?
    Externally it's just a dust cover. The bleed nipple on the RS785 brakes operates in a different way than the older ones I believe. The valve is independent from the screw that is used to open up the bleed port.

  7. #7
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    Quote Originally Posted by Migen21 View Post
    Lot's of things are possible. Maybe the seal didn't get put back in when you bled them?
    There is no 'seal' so that's not it.

    Quote Originally Posted by alxrmrs View Post
    Externally it's just a dust cover. The bleed nipple on the RS785 brakes operates in a different way than the older ones I believe. The valve is independent from the screw that is used to open up the bleed port.
    ^This^ The syringe/hose go on the bleed nipple and you allow fluid to flow into/out of the caliper by opening the system w/ a completely separate screw.

    Quote Originally Posted by allenpg View Post
    When I get oil on my pads or other residue, I just burn it off with a butane torch. Squeaking goes away!
    If brake pads get brake fluid or mineral oil on them they are ruined. There are NO ifs ands or buts about this...they are done and need to be replaced. Oiled pads don't always squeak, so this might not be the problem in many 'squeaky brake' cases.

    And for the OP: As others have posted there is no 'blow-off' valve on any brake system. Ever. If you can't inspect your brake/rotor and determine whether there is possibly fluid on the pads you need to take your bike to someone that is able to do this before you ride it again. And...you shouldn't be mixing SRAM rotors and Shimano pads. There will be no fiery crashes but you should ALWAYS match pads and rotors. They are most definitely engineered to work together.
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    [QUOTE=cxwrench;5159371 If brake pads get brake fluid or mineral oil on them they are ruined. There are NO ifs ands or buts about this...they are done and need to be replaced. Oiled pads don't always squeak, so this might not be the problem in many 'squeaky brake' cases. [/QUOTE]

    Do you have a link to what this looks like visually so I can figure out if they got contaminated? I seemed to have good braking power after the system cooled down.

    And for the OP: As others have posted there is no 'blow-off' valve on any brake system. Ever. If you can't inspect your brake/rotor and determine whether there is possibly fluid on the pads you need to take your bike to someone that is able to do this before you ride it again. And...you shouldn't be mixing SRAM rotors and Shimano pads. There will be no fiery crashes but you should ALWAYS match pads and rotors. They are most definitely engineered to work together.
    I understand that the pads and rotors are made to work together but was this incident a direct result of mixing and matching? It's hard to tell. Also, how can I tell if there is any permanent damage to the caliper and if I need to do more than top up the mineral oil.

  9. #9
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    Quote Originally Posted by alxrmrs View Post
    Do you have a link to what this looks like visually so I can figure out if they got contaminated? I seemed to have good braking power after the system cooled down.



    I understand that the pads and rotors are made to work together but was this incident a direct result of mixing and matching? It's hard to tell. Also, how can I tell if there is any permanent damage to the caliper and if I need to do more than top up the mineral oil.
    It looks (and feels...you'll get it on your fingers if it's there) like oil. Look at it. Pull the wheel and take the pads out, you'll know. If there is oil on the outside of the brake...anywhere...you need to find out what the problem is before you ride it again. Absolute must.

    If fluid has leaked from the system, you need to bleed it. There is no such thing as 'topping up the fluid'. You MUST perform a brake bleed. Absolute must. I don't see how you could have damaged the caliper by heavy braking. The legions of short sleeved button down shirts w/ pocket protector wearing Shimano engineers have made sure that these brakes will survive anything that you can do to them. You can drag them down a miles long descent and boil the **** outta the fluid resulting in air bubbles in the system and all you have to do is bleed them. Possibly replace the pads/rotor. Like I said previously, you can use the mis-matched pads/caliper and rotors but the brakes will never work as well as they could w/ properly matched parts.

    As for how you brake in situations like this, don't drag them continuously...brake, coast, brake, coast. You never said whether this was the front or rear brake. Your rear brake doesn't do much to slow you down but it does a wonderful job of creating tons of heat and wearing out parts. The front brake is what slows you down. Look at brake systems on motorcycles (especially sport bikes) and cars. You'll immediately see what I'm talking about.
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    The pads aren't expensive. Just replace them if you aren't sure.

    Did your rotors discolor from the heat? Is there any bluing?

    The type of pads you use matters.

    Here is a video with some background on disc brakes.

    https://youtu.be/0HFfQfv1qys

  11. #11
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    Quote Originally Posted by Migen21 View Post
    Here is a video with some background on disc brakes.

    https://youtu.be/0HFfQfv1qys
    Interesting. I don't yet own a disc brake bike. The gravel bike I am considering has Shimano BR-RS505 hydraulic disc brakes with resin pads, Centerlock Ice Tech 160mm rotors and Shimano ST-RS505 Dual Control STI levers.

    This thread on brake fluid leaking has obviously raised a concern for me even though it may be something out of the ordinary. Maybe it's just because I'm a "disc novice". As they say, ignorance breeds fear.

    This question is for CXWrench or any other shop mechanics here. Have you seen any failures or other noteworthy concerns on these particular brakes? Is there a mileage or time schedule I should have them bled? Since I store my bikes inside the house instead of the garage, basement or shed, can I assume fluid changes need to be done less often due to less swings in humidity? I am also assuming the front and rear brakes work independently, so in the unlikely event I get air in the system or the fluid boils and I lose braking, the other brake will still work, correct?

    Thanks all for your input!
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    I have yet to see a brake failure that was not 100% avoidable. The most common thing I see is contamination from people being sloppy with chain lube or while washing their bike. DOT systems (Avid/SRAM) should be flushed annually to prevent seal degradation. Mineral systems (Shimano) are much more stable and personally do mine every other year for piece of mind.
    I think the biggest complaint I get in the shop is disc noise. Once you learn how to properly align the calipers it's a non-issue. The method of squeeze brake, loosen and tighten bolts is not good practice, it takes more effort to really get it spot on. Once you 'get it' it doesn't take more than a minute to dial them in.
    While I have 'heard' of failures, I'm sure everyone has, I haven't seen any in person that would classified as catastrophic. No more serious than what I've seen with rim brakes.

  13. #13
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    No 'failures' as such. As rcb posted, any problems are usually caused by some type of contamination of the pads by chain lube or improper cleaning. Every car, motorcycle, airplane...pretty much anything that has wheels has hydraulic brakes. All of these systems are well engineered and work great when set up properly. I wouldn't worry about them at all.
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    Ahhhh, OK. It sounds like problems are largely due to "user error" and that failures are no more likely than on rim brakes. As you said, CX, cars have had hydraulic brakes (drum and then disc) for at least our lifetime. I can remember growing up with cars that had brake failures where pumping saved the day (worn out master cylinder). Don't know if that would work on bike systems in the same event of something like air in the system or fluid boiling.

    I can't get over how many people take a garden hose to their bike to wash it. My bike cleanings are a wipe-down, never running water. And I can imagine contamination from chain lube could be a problem if you don't wipe the excess off after lubing.

    Thanks guys!
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  15. #15
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    Quote Originally Posted by Lombard View Post
    Interesting. I don't yet own a disc brake bike. The gravel bike I am considering has Shimano BR-RS505 hydraulic disc brakes with resin pads, Centerlock Ice Tech 160mm rotors and Shimano ST-RS505 Dual Control STI levers.

    This thread on brake fluid leaking has obviously raised a concern for me even though it may be something out of the ordinary. Maybe it's just because I'm a "disc novice". As they say, ignorance breeds fear.

    This question is for CXWrench or any other shop mechanics here. Have you seen any failures or other noteworthy concerns on these particular brakes? Is there a mileage or time schedule I should have them bled? Since I store my bikes inside the house instead of the garage, basement or shed, can I assume fluid changes need to be done less often due to less swings in humidity? I am also assuming the front and rear brakes work independently, so in the unlikely event I get air in the system or the fluid boils and I lose braking, the other brake will still work, correct?

    Thanks all for your input!
    Modern disc systems have a ton of engineering hours put into them. EARLY hydraulic disc systems for road (think 5+ years ago), didn't have adequate cooling on rotor/caliper resulting in fluid boiling if you rode the brakes on a mountain road descent. These days, not a thing. It is a standard test now to show off by reviewers, picking the worst steep long mountain descent and riding the brakes and looking for brake fade. But people have been singing praises of Shimano's brakes, in reviews, for years now. SRAM's (honestly) a bit less so. The two systems each have their own little universe of traits. One side tends to get air past seals over time, the other tends to get grime in over time. Most people like Shimano's bleeding method over SRAMs. Some prefer SRAM's DOT fluid over Shimano's mineral oil.


    When setup right and well, there's not much to worry about. The maintenance, if you pay a shop, is a bit more expensive (bleeding versus swapping cables). But you never have to worry about wheel rims being worn out. Only thing is keep lubricants away from the rotors and pads.

    Quote Originally Posted by Lombard View Post
    Ahhhh, OK. It sounds like problems are largely due to "user error" and that failures are no more likely than on rim brakes. As you said, CX, cars have had hydraulic brakes (drum and then disc) for at least our lifetime. I can remember growing up with cars that had brake failures where pumping saved the day (worn out master cylinder). Don't know if that would work on bike systems in the same event of something like air in the system or fluid boiling.
    Quote Originally Posted by Lombard View Post

    I can't get over how many people take a garden hose to their bike to wash it. My bike cleanings are a wipe-down, never running water. And I can imagine contamination from chain lube could be a problem if you don't wipe the excess off after lubing.

    Thanks guys!



    LOL, such a roadie. Maybe we can get you into CX, then you'd understand.
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    Quote Originally Posted by Marc View Post

    LOL, such a roadie. Maybe we can get you into CX, then you'd understand.
    LOL! Nope, I'm a fair weather gravel/dirt rider. My mountain bike can get quite grungy, but nothing I can't wipe clean with a cloth wet with water or alcohol. Not to mention a mountain bike is supposed to look dirty. I thoroughly clean the important functional things like the drivetrain.
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  17. #17
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    Quote Originally Posted by Lombard View Post
    LOL! Nope, I'm a fair weather gravel/dirt rider. My mountain bike can get quite grungy, but nothing I can't wipe clean with a cloth wet with water or alcohol. Not to mention a mountain bike is supposed to look dirty. I thoroughly clean the important functional things like the drivetrain.
    Don't worry about getting your bike wet to wash it. I wash the **** outta pretty much every bike I work on at the shop, disc brakes or not. You just have to be smart about it. If you're not hosing it off and getting suds everywhere you're not washing it.
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    What he said. What I meant when I said washing the bike, was people that use rag to wipe everything down, disc included, regardless of whether or not they just wiped the chain with that same rag. Basically people just being careless.
    As for the OPs issue, did you check to see if that allen head set screw that opens and closes the bleed valve was secure? If it wasn't, then there's the reason for fluid coming out the bleed port. Another common source of problems is people squeezing the lever with the wheel out and dislodging the piston. If that happens, just stop and bring it to a shop. Don't just try to jam the thing back in there. Seen plenty of chipped and cracked pistons from that.

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    I finally got around to inspecting the bike. I pulled both the front and rear pads and couldn't notice any difference between them. Both were a bit dirty but I wiped them down with a clean cloth. I didn't perform a full bleed of the system (the whole system is less than a few months old) but I did open up the top screw on the shifter and put on the oil funnel with oil inside and get any air I could out of the system with a bleed block in the caliper. The brakes are now extremely strong and I see no point in performing a full bleed (i.e. opening up the screw at the bottom and pushing fluid through the bleed port).

    I managed to find a replacement seal for the bleed port and am waiting for that to arrive.

    From the posts above it doesn't seem as if I could have broken a seal on the bleed port and continue to leak fluid. Could someone verify that this is actually correct?

    The pistons looks fine without any sign of damaging. The one thing I did notice is that rotors may have some signs of overheating as they have some "heat streaking" on them. Link to pic: Imgur: The most awesome images on the Internet

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