Hydraulic Braking issue
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  1. #1
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    Hydraulic Braking issue

    Hey everyone.

    I recently had all my components/ drivetrain professionally (lbs) swapped from one frame set to another. Both are OPEN Up Frame sets. Brake rotors and pads unchanged. Pads are approximately 3 months old. No wet riding during this period.

    Drivetrain is the 2018 Ultegra Di2 Hydraulics 1x with XTR rear derailleur. Before the swap, braking worked flawlessly. After the swap, the rear brake just doesn’t engage properly. That is, it’s so unresponsive. The lever has to be fully depressed to get the brake to engage. And even then, braking is very “weak”. Front brake absolutely no issue.

    Shop did a quick rebleed, stating likely due to air bubble in the system. This seemed to solve the issue for 3/4 of one ride. . Then same issue arose. Brought her back to shop. They did a more “complete “ (?) rebleed. This time, rear brake worked fine for two rides. On the third, same thing! Brake just wouldn’t engage properly.

    Planning on bringing her back. But would love to hear about other probable causes besides air bubbles. And if due to air bubbles, do I have them rebleed again? Just trying to figure out why this keeps happening.

    Thank you! B7C9DA90-54BB-4597-9F81-B3ADC70A540C.jpg
    Last edited by Cni2i; 06-23-2019 at 05:39 AM.
    EyeGuy

  2. #2
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    I'm thinking somehow in this process, the rear brake lever was depressed while the wheel was out. Usually this results in brake rub, but I am thinking what is possibly going on here is that one pad is making contact with the disc before the other, thereby giving you a loss of braking power.

    You may want to have your shop reset the calipers. They will have to spread them. It's a fairly easy process.
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  3. #3
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    Quote Originally Posted by Cni2i View Post
    Hey everyone.

    I recently had all my components/ drivetrain professionally (lbs) swapped from one frame set to another. Both are OPEN Up Frame sets. Brake rotors and pads unchanged. Pads are approximately 3 months old. No wet riding during this period.

    Drivetrain is the 2018 Ultegra Di2 Hydraulics 1x with XTR rear derailleur. Before the swap, braking worked flawlessly. After the swap, the rear brake just doesn’t engage properly. That is, it’s so unresponsive. The lever has to be fully depressed to get the brake to engage. And even then, braking is very “weak”. Front brake absolutely no issue.

    Shop did a quick rebleed, stating likely due to air bubble in the system. This seemed to solve the issue for 3/4 of one ride. . Then same issue arose. Brought her back to shop. They did a more “complete “ (?) rebleed. This time, rear brake worked fine for two rides. On the third, same thing! Brake just wouldn’t engage properly.

    Planning on bringing her back. But would love to hear about other probable causes besides air bubbles. And if due to air bubbles, do I have them rebleed again? Just trying to figure out why this keeps happening.

    Thank you! B7C9DA90-54BB-4597-9F81-B3ADC70A540C.jpg
    The shop handed the bike off to you and the rear brake didn't work properly?!? The frame has internal routing so they'd have to separate the hose at one end to get it through the frame. This would normally necessitate a bleed. There is only ONE way to bleed a brake, that is putting fluid in at one end and having fluid/air come out at the other end. There is no 'partial' or 'quick' bleed. If the process is done correctly there should be no problems. Sounds to me like your shop is not following the correct procedure.

    Quote Originally Posted by Lombard View Post
    I'm thinking somehow in this process, the rear brake lever was depressed while the wheel was out. Usually this results in brake rub, but I am thinking what is possibly going on here is that one pad is making contact with the disc before the other, thereby giving you a loss of braking power.

    You may want to have your shop reset the calipers. They will have to spread them. It's a fairly easy process.
    What? When you bleed a brake both pistons are pressed back into the caliper and a bleed block is inserted. The pads are removed. You don't 'reset' calipers, you push pistons back.
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  4. #4
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    Quote Originally Posted by cxwrench View Post
    What? When you bleed a brake both pistons are pressed back into the caliper and a bleed block is inserted. The pads are removed. You don't 'reset' calipers, you push pistons back.
    OK, I used the wrong terminology. When I said reset, I meant pushed back.

    On the bleed issue, I stand corrected - provided the shop did it correctly the way you said.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein



  5. #5
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    Quote Originally Posted by cxwrench View Post
    The shop handed the bike off to you and the rear brake didn't work properly?!? The frame has internal routing so they'd have to separate the hose at one end to get it through the frame. This would normally necessitate a bleed. There is only ONE way to bleed a brake, that is putting fluid in at one end and having fluid/air come out at the other end. There is no 'partial' or 'quick' bleed. If the process is done correctly there should be no problems. Sounds to me like your shop is not following the correct procedure.
    This is 100% correct. I only a novice not a professional bike mechanic. With a minor cost for tools you can do this yourself. Bought hydraulic brakes for my CX bike. Hose was to short so I had to replace. Followed Shimano’s detailed instructions and had no problem. Installed the funnel at brake lever and injected fluid into bleed screw and pushed air and fluid into funnel. Then proceeded to pump brake and crack bleeder. Worked perfectly. Also lots of YouTube videos on this.

  6. #6
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    Thanks for the replies guys.

    Cxwrench: when they handed my bike back, all was well for part of the first ride. About 1/2 way through the ride, the rear brake issue reappeared. I brought her back in and the mechanic rebled the brake system. Tbh, not sure exactly what/how he did it. I just took his word for it, that he would rebleed the system to flush out all air bubbles. The second time around, the rear brake worked “normal” for two rides. On the third ride, the same issue reappeared?!?! Just not sure why it would work fine for two full rides then stopped working properly all of a sudden.

    I was planning on dropping the bike in today after my morning ride. Okay, so the first 1/3 of the ride, rear brake was faulty as expected. But then, it started to spontaneously engage better again?! Maybe still not quite as good as the front brake, but about 85% as good. Again, I’m definitely not a wrench, so not sure what’s going on. Could repeated pressing of the brake lever move the air bubble out???

    Apologies for the confusion, but I’m confused myself. Just wanted to get feedbacks from you guys so I can relay sensible info to the shop mechanic.

    Ty.
    EyeGuy

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    Quote Originally Posted by Cni2i View Post
    Thanks for the replies guys.

    Cxwrench: when they handed my bike back, all was well for part of the first ride. About 1/2 way through the ride, the rear brake issue reappeared. I brought her back in and the mechanic rebled the brake system. Tbh, not sure exactly what/how he did it. I just took his word for it, that he would rebleed the system to flush out all air bubbles. The second time around, the rear brake worked “normal” for two rides. On the third ride, the same issue reappeared?!?! Just not sure why it would work fine for two full rides then stopped working properly all of a sudden.

    I was planning on dropping the bike in today after my morning ride. Okay, so the first 1/3 of the ride, rear brake was faulty as expected. But then, it started to spontaneously engage better again?! Maybe still not quite as good as the front brake, but about 85% as good. Again, I’m definitely not a wrench, so not sure what’s going on. Could repeated pressing of the brake lever move the air bubble out???

    Apologies for the confusion, but I’m confused myself. Just wanted to get feedbacks from you guys so I can relay sensible info to the shop mechanic.

    Ty.
    I’m just an amateur mechanic too; I’ve set up and bled hydraulic brakes half a dozen time or so. And everything cxwrench said should be the final word on how you bleed brakes.

    But I agree with you, OP: the fact that the firmness of the brake lever seems to be changing during and between rides – that doesn’t make any sense.

    In my experience, if the brakes aren’t bled properly (if there are air bubbles in the system) then the brake lever is mushy. If the brakes ARE bled properly, the lever is firm and the brakes are solid.

    But the hydraulic system is supposed to be a closed system: you should not be able to “flush the air out” while riding the bike. I genuinely don’t understand how the brakes are going from good to bad and back again. And this makes me wonder if there is something else or something more wrong than the hydraulic bleed – like something going on in the brake caliper or in the master cylinder in the hood. Maybe a piston is sticking and then unsticking...

    I dunno, but the theory that the brakes weren’t bled properly is not enough to explain the phenomena you are reporting to us here. It may be that the brakes weren’t bled properly, but it’s not only that...

  8. #8
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    This is a timely youtube channel update from Park Tools showing in detail how your hydryaulic brake pistons work.


  9. #9
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    Quote Originally Posted by fronesis View Post
    I’m just an amateur mechanic too; I’ve set up and bled hydraulic brakes half a dozen time or so. And everything cxwrench said should be the final word on how you bleed brakes.

    But I agree with you, OP: the fact that the firmness of the brake lever seems to be changing during and between rides – that doesn’t make any sense.

    In my experience, if the brakes aren’t bled properly (if there are air bubbles in the system) then the brake lever is mushy. If the brakes ARE bled properly, the lever is firm and the brakes are solid.

    But the hydraulic system is supposed to be a closed system: you should not be able to “flush the air out” while riding the bike. I genuinely don’t understand how the brakes are going from good to bad and back again. And this makes me wonder if there is something else or something more wrong than the hydraulic bleed – like something going on in the brake caliper or in the master cylinder in the hood. Maybe a piston is sticking and then unsticking...

    I dunno, but the theory that the brakes weren’t bled properly is not enough to explain the phenomena you are reporting to us here. It may be that the brakes weren’t bled properly, but it’s not only that...
    Thank you for that explanation. Yeah, each time he bled the brake system, braking was firm and engaged as expected. But then like I said, it goes bad again. Happened twice as mentioned above. But when it became spontaneously firmer again during the ride...I was like “phew”...but had me scratching my head wondering what’s going on. I’ll mention some of the things you mentioned to the mechanic this week.
    EyeGuy

  10. #10
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    When you pick the bike up put it up on the rear wheel, vertical. Pull the levers a bunch and see if they stay firm. A LOT of times this will let air in the system to work it's way to the master/lever and the brake will get soft. I always do this after a bleed just to make sure.
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  11. #11
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    Quote Originally Posted by cxwrench View Post
    When you pick the bike up put it up on the rear wheel, vertical. Pull the levers a bunch and see if they stay firm. A LOT of times this will let air in the system to work it's way to the master/lever and the brake will get soft. I always do this after a bleed just to make sure.
    Thank you. I will.
    EyeGuy

  12. #12
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    Quote Originally Posted by cxwrench View Post
    When you pick the bike up put it up on the rear wheel, vertical. Pull the levers a bunch and see if they stay firm. A LOT of times this will let air in the system to work it's way to the master/lever and the brake will get soft. I always do this after a bleed just to make sure.
    That makes a lot of sense: it explains how a system that wasn't bled properly might not immediately reveal itself as problem. But once the air bubbles make their way up into the master cylinder, you get a mushy lever. (My bike rack at home holds my bike vertical this way, so a crappy bleed shows itself immediately.)

  13. #13
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    If they are doing the bleeding procedure correctly there may be a leak somewhere in the system that's allowing more air to eventually find its way inside. Perhaps they buggered up something when reattaching the hose after routing it through your frame? Check to see if any brake fluid is visible at hose connections, bleed/fill ports, etc.

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