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  1. #1
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    derailleur cables in disc brakes

    I have heard of some people using derailleur cables with their disc brakes- derailleur cables are supposed to be less stretchy than brake ones, and therefore have better power transfer. I have a few questions about this.
    1) Is this in any way dangerous?
    2) How much of a difference does this make?
    3) The barrel head of a derailleur cable is different than the barrel head of a brake cable. How does a derailleur cable barrel head fit in a brake lever?
    4) I have to suppose that people who use derailleur cables on their brakes continue to use brake cable housing. What if I switch to Nokon derailleur cables with my brakes- should I use the brake housing or derailleur housing?
    Thanks.
    undefined Absolutely must have: Black Machine Tech Zeroflex brake levers (the ones with the rotating leverage adjuster)

  2. #2
    T.W.O.
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    You can certainly try it. The brake housing is design for better modulation not compression. Who knows may be it would work better for you.

  3. #3
    ballbuster
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    Uh, I dunno where you heard that, but brake cables are waaaay less stretchy than derailleur cables.

    Also, the housing makes a bigger difference than the cable.

    Also, for Avid Mechs to work, you really should get the stiffest cables and housing you can find.

  4. #4
    rebmem rbtm
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    This PHOTO shows what can happen if you use shifter housing instead of brake housing.

    Types of Cable Housing:

    Conventional Spiral Housing
    At first glance, many people assume that cable housing is made of plastic. Actually, it is steel, and the plastic is a covering to protect it from moisture, and to keep it from scratching the paint of the bicycle.

    Traditional cable housing is a tightly-wrapped spiral of steel wire, sort of like a small-diameter Slinky. It has no particular strength in tension (pulling) but it cannot be compressed because the coils of wire are tight against one another.

    Through the 1970's, the inner wire ran right through the steel spiral housing, usually using grease for lubrication. Modern housing, however, has a plastic liner which surrounds the inner wire. This considerably reduces the friction. Some high-end cable systems, such as the Gore-Tex "Ride-On" cables, extend this liner even along the areas where there is no housing. These systems also have a special friction-reducing coating on the inner wires.

    Compressionless "Index-compatible" Housing
    With the advent of indexed shifting combined with handlebar mounted shift levers, it developed that conventional housing was a source of imprecise shifting. This is because the effective length of the housing changes as it is bent. This is not a problem with brakes: Although sometimes it will be noted that rear brakes may drag slightly when the handlebars are turned all the way to one side, you can't turn the bars that far when the bike is actually in motion.

    The small variation in housing length was too much for reliable indexed shifting, however, so Shimano introduced "S.I.S." housing, now widely copied by other manufacturers. This type of housing does not consist of a single spiral-wound wire, but instead, it has a bundle of wires running pretty much straight along parallel to the housing. They are held in place by being sandwiched between the plastic housing liner and the plastic outer covering.

    "Compressionless" housing doesn't change length significantly as it is flexed, so the indexed shifter is able to communicate the correct setting to the derailer, even as the handlebars are turned, and the loops of cable housing bounce up and down due to bumps.

    Warning: Since compressionless housing relies on plastic to hold it together, it is not as strong as conventional spiral housing, and should never be used for brakes! The loads applied to brake cables can easily cause compressionless housing to rupture and burst, causing a complete and sudden loss of brake function.

    http://www.sheldonbrown.com/cables.html

  5. #5
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    Thanks.
    I suspected this was the case- I have cut shift housing, and the longitudinal strands do not like they would hold up.
    What about the cables themselves? I know I've heard of people using them for brakes, but don't know still how big of an advantage that gives, and how you can make shift cable barrels sit in a brake lever.
    undefined Absolutely must have: Black Machine Tech Zeroflex brake levers (the ones with the rotating leverage adjuster)

  6. #6
    rebmem rbtm
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    Derailleur Cables are usually 1.1mm or 1.2mm

    Brake Cables are usually 1.5mm or 1.6mm

    Which cable would be able to endure a much greater amount of tensile (pulling) force ?

    Would the smaller cable be more likely to stretch then the bigger cable ?

    Apart from the cable end on the derailleur cable not usually matching up with the brake levers is the cable clamp on the brake designed to be used with the smaller diameter derailleur cable and will it clamp this cable as well as it will with the larger diameter brake cable ?

    A few threads on this subject:
    Derailleur vs Brake cable sizes
    shifter cable in brake housing?
    Brake vs Derailleur cable swappable?
    Shifter cables & housing with disc brakes
    So THAT is why my brakes have no stopping power

    .
    Last edited by cobba; 10-20-2011 at 11:10 PM.

  7. #7
    Tool
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    One of the reasons shift and brake cables have different terminations is to discourage people from using shift cables on brakes. The other posters have provided lots of good info as well.

    -Pete
    I can barely get my mouth around it.

  8. #8
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    Your brakes will definitely have a firmer feel when you use derailleur housing. I prefer the feel of regular brake housing because it has more modulation. I had to use metal ferrules when I used the derailleur cable set-up on my BB7s, and after a few months the metal derailleur cable strands worked their way through the hole on the metal ferrule. This caused a mushy feeling that was dangerous and the frayed cable end stabbed me. Saving a few extra grams is not worth it.

  9. #9
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    Quote Originally Posted by cobba View Post
    Warning: Since compressionless housing relies on plastic to hold it together, it is not as strong as conventional spiral housing, and should never be used for brakes! The loads applied to brake cables can easily cause compressionless housing to rupture and burst, causing a complete and sudden loss of brake function.
    Sheldon is a saint, but this information has been out of date for years there's now truly compressionless universal housing that has straight strands on the inside and a spiral winding on the outside. Widely available brand names include Yokozuna Reaction and Jagwire Ripcord.

    Yes, it's expensive and generally only comes in kit form (Torelli sells it in bulk). It's also extremely stiff and does not want to go around tight bends at all.

    But it does not compress AT ALL, and makes BB7s perform fantastically. The road versions are almost unusable without this type of housing.

  10. #10
    workin' it Administrator
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    Ok: cables no you can not use derailleur cables on a brake and vice versa as they have different heads that don't work on opposite types of uses. The Brake uses a big round head and the derailleur a small round head. Won't work.

    Then what everyone said about the housing is also true. There is a reason it is called brake cable and housing and Derailleur cable and housing.
    Try this: HTFU

  11. #11
    Plays with tools
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    Using standard shift housing will feel great until it blows out at which point it won't work at all. It's a death trap waiting to happen. However the housing the blasdef mentioned is perfect although I wouldn't call it universal. Brake cables are for, you guessed it brakes. Anybody that is trying to use shift cables is either in a really tight spot or asking for trouble.

  12. #12
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    The Reaction-style housing really is universal, stronger than normal brake housing and less compressible than normal derailleur housing.

    The problem you run into with using it for shifting is that it's too stiff to make it around a lot of common derailleur cable bends, and since it's slightly bigger than normal 5mm brake housing (you use it without ferrules, or with special ones that come in the kit), there's no way it would fit where normal 4mm derailleur housing would.

    That being said, it's perfect for use with Shimano Alfine gear hubs as a full housing run.

    You're right about never using shift cables for braking since they're significantly smaller in diameter, but it's not like he could even really get started using them with discs the cable ends wouldn't fit in the brake levers, and it would slip out of the groove in the clamp on most calipers

  13. #13
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    Quote Originally Posted by blasdelf View Post
    The Reaction-style housing really is universal, stronger than normal brake housing and less compressible than normal derailleur housing.
    The reason I think it's not universal is because of the ID. It's sized for a brake cable and I've never been truly happy when using that kind of housing when running shift cables. Sure it 'will work' but it's not good enough in my shop.

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