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  1. #1
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    Shortening hoses

    Ok this might be a dumb question

    I need to shorten my hoses and I don't want to bleed my brakes

    Do I remove the hoses at the master cylinder or caliber so there is as little air as possible
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  2. #2
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    You adjust length at the lever.

    You will likely need to bleed your brakes afterwards.

  3. #3
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    I've shortened the hoses on my Magura Marta brakes without the need to bleed. I followed their instructions carefully (readily available on their website), and I'm sure it helps if you have a basic understanding of hydraulics, and how air typically enters a system. Magura instructions offer some common-sense advice along those lines such as first positioning your MC (lever) so that the hose connection is at the highest point of the entire system. Once you've carefully disconnected the hose, perform all cutting carefully but quickly keeping the hose at a high elevation relative to the rest of the brake system. Lastly, make sure you have all the new sealing ferules and compression fitting parts necessary for a quick re-connection.

    Certain systems will probably require a bleed after a shortening procedure no matter how careful you are, but I think a quick, carefully planned operation using one's basic knowledge of hydraulics can help prevent having to bleed.

  4. #4
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    Before shortening it, you can remove the pads and extend the pistons by pulling the brake lever. Be careful - you will pop the pistons out if you go to far. This will move more fluid out of the reservoir and into the caliper. Any air that gets into the line will be pushed out when you push the pistons back in.

  5. #5
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    Quite frankly the procedures you would have to go through to try and avoid bleeding the system seem more complicated than it would be to just bleed the system.

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    Quote Originally Posted by rlouder View Post
    Before shortening it, you can remove the pads and extend the pistons by pulling the brake lever. Be careful - you will pop the pistons out if you go to far. This will move more fluid out of the reservoir and into the caliper. Any air that gets into the line will be pushed out when you push the pistons back in.
    I used this method with my new XT brakes yesterday, and it worked great. It's a lot less complicated than adding bleeding into the mix.

  7. #7
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    Quote Originally Posted by rlouder View Post
    Before shortening it, you can remove the pads and extend the pistons by pulling the brake lever. Be careful - you will pop the pistons out if you go to far. This will move more fluid out of the reservoir and into the caliper. Any air that gets into the line will be pushed out when you push the pistons back in.
    I have to point out a flaw in this logic. I don't doubt you guys are successfully shortening hoses without bleeding, but it has nothing to do with this maneuver.

    In essence a hydraulic brake system is a closed system. In other words, there is no way to push any air out that may have gotten in simply through outward movement of the pistons. There is no magic escape route for the trapped air. The air merely compresses in the system whereas the brake fluid does not. This is why air that has somehow found its way into the system is so detrimental to performance.

    The only way to get air out is to perform a bleed, a procedure whereby you open the system up at both ends and flush oil through it, thus purging every nook and cranny of any trapped air. A bleed is then completed by closing the system back up.

    My advice is to stop risking popping a caliper piston out, which is the only thing this maneuver actually will accomplish.

  8. #8
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    Quote Originally Posted by Betarad View Post
    I have to point out a flaw in this logic. I don't doubt you guys are successfully shortening hoses without bleeding, but it has nothing to do with this maneuver.

    In essence a hydraulic brake system is a closed system. In other words, there is no way to push any air out that may have gotten in simply through outward movement of the pistons. There is no magic escape route for the trapped air. The air merely compresses in the system whereas the brake fluid does not. This is why air that has somehow found its way into the system is so detrimental to performance.

    The only way to get air out is to perform a bleed, a procedure whereby you open the system up at both ends and flush oil through it, thus purging every nook and cranny of any trapped air. A bleed is then completed by closing the system back up.

    My advice is to stop risking popping a caliper piston out, which is the only thing this maneuver actually will accomplish.
    When you re-insert the pads... it will back-flow the brake fluid into the reservoir. If the air-bubble is close to the reservoir, it ALSO goes into the reservoir. Where it sits, ABOVE the action of the brakes... you know, with that air gap that already exists right there.

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    Perhaps certain systems may allow operation as you describe, I'm not familiar with all of them. However, while my Magura Martas do indeed utilize an air gap at the master cylinder to compensate for variables in fluid volume due to heat expansion and pad wear, my understanding is the air is securely separated from the fluid itself by a bladder. How does air in the fluid get from one side of the bladder, where it is detrimental, to the other side where it is harmless?

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    Not sure what this bladder you speak of is (i dont have a reason to not use one, just haven't seen them myself)... But some brakes (like the ones in your car) have no separation. Brakes lines are sized to maintain a capillary lock on fluid (think putting you finger over a straws end and pulling it out of a cup... But in this case the fluids surface tension is the "finger") in order to keep air out. In the reservoir, located above the master cylinder, there is air at the top to perform the functions you described. Gravity keeps them separate for the most part... With the fluid being heavier than air.

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    I'm in total agreeance on your car analogy, and there certainly may be mountain bike systems that operate identically. However, I still think the use of a rubber bladder in the MC reservoir is prevalent in mountain bike specific systems. Our fluid reservoirs are minuscule in capacity by comparison, and are constantly bouncing around, and bikes are routinely placed or stored upside down with no ill-effect to the system. Surely a system as you describe would introduce some of the air in the air gap into the lines if placed upside down for any length of time?

    BTW, I'm not trying to be argumentative here....this is a great discussion on a subject I know just enough to be dangerous on, and want to know more about. Hope you see it the same way.

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    If the master cylinder was closed, the reservoir is sealed off from the system.

    Master cylinder also fills by capillary action or positive pressure pump. And only enough to compensate for brake pad wear, as you aren't using a cycling fluid system.

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  13. #13
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    Sometimes you can get away without bleeding but its not for sure so I would just bleed them as to not have issues later.

  14. #14
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    I found this on a web search, I had no idea Hayes holds (or at least held) the patent on what is pretty much the industry standard brake system.

    Patent EP1007404A2 - Bicycle brake system - Google Patents

    Sums up the unique requirements of a mountain bike system pretty well.

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    Well... how about this:

    if you have a "bladder"... bleed it.

    if you don't... then you 'can' do it the risky way...

    But you should probably bleed the system occasionally anyways... brake fluid does NOT last forever, even in a sealed environment without much heat cycling going on.

  16. #16
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    Quote Originally Posted by Betarad View Post
    I have to point out a flaw in this logic. I don't doubt you guys are successfully shortening hoses without bleeding, but it has nothing to do with this maneuver.

    In essence a hydraulic brake system is a closed system. In other words, there is no way to push any air out that may have gotten in simply through outward movement of the pistons. There is no magic escape route for the trapped air. The air merely compresses in the system whereas the brake fluid does not. This is why air that has somehow found its way into the system is so detrimental to performance.

    The only way to get air out is to perform a bleed, a procedure whereby you open the system up at both ends and flush oil through it, thus purging every nook and cranny of any trapped air. A bleed is then completed by closing the system back up.

    My advice is to stop risking popping a caliper piston out, which is the only thing this maneuver actually will accomplish.
    You're wrong. Air does not mix with the fluid (compress into the system?).

    I wasn't very specific because most people would know to wait until after you cut the line and reconnect it before pushing the pistons in. This system is open when the line is off the lever - not closed. Air will be introduced but stay at that level (unless you turn the bike upside down). Fluid is heavier than air. After one reconnects the line, they would open the reservoir cover and remove the bladder before pushing in the pistons

    In essence, it's a mini bottom-up bleed. Only a small amount of fluid is needed due to the location of the air. Thus, you don't have to extend the pistons very far. If someone did push a piston out, it's no big deal. You just push it back into the caliper, shorten the line, then bleed.

    Hope this helps explain it. It's useful if someone doesn't have a bleed kit. Perhaps it will help someone else if you're just bull****ing us.

  17. #17
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    Well...thanks for filling in some important blanks. Like the fact you're now removing the reservoir cover and bladder. Kinda changes the story significantly, don't you think?

    Now that you've made that clear, I agree this maneuver can help avoid a full bleed. I'd still steer clear of it and just perform a bonafide bleed. After all, bleeding the system isn't rocket science.

    As far as your snide comment about me bull****ing anyone goes, perhaps you should review the advice given in your initial post. Do you really think someone seeking advice on an unfamiliar subject is going to correctly assume they're really performing a "mini bottom-up bleed" and need to remove the reservoir cover? (without inadvertently introducing even more air into the system).

  18. #18
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    Quote Originally Posted by Betarad View Post
    I've shortened the hoses on my Magura Marta brakes without the need to bleed. I followed their instructions carefully (readily available on their website), and I'm sure it helps if you have a basic understanding of hydraulics, and how air typically enters a system. Magura instructions offer some common-sense advice along those lines such as first positioning your MC (lever) so that the hose connection is at the highest point of the entire system. Once you've carefully disconnected the hose, perform all cutting carefully but quickly keeping the hose at a high elevation relative to the rest of the brake system. Lastly, make sure you have all the new sealing ferules and compression fitting parts necessary for a quick re-connection.

    Certain systems will probably require a bleed after a shortening procedure no matter how careful you are, but I think a quick, carefully planned operation using one's basic knowledge of hydraulics can help prevent having to bleed.
    I've done the same with my Martas as well. Used the youtube vids from Magura as a guide. I was a bit leery the first couple rides around the block but in the end the brakes are spot on.

    Avid and Hope brakes are a different story. Had to do a complete bleed on those.
    Amolan

  19. #19
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    Quote Originally Posted by Betarad View Post
    Well...thanks for filling in some important blanks. Like the fact you're now removing the reservoir cover and bladder. Kinda changes the story significantly, don't you think?
    Well, I don't know about the systems you guys are using, but I didn't remove a bladder or open the reservoir on the new XTs, and it worked just fine. This is the method Shimano recommends for shortening lines in their own tech bulletins, by the way.

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