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  1. #1
    RidesOldTrek
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    Brake Cable Housing Standard - Question

    My question is about brake cable sizing standards. It seems like 5mm is the standard, but I know that 6mm cables were used in the past. The problem is that 5 mm doesn't seem to work on my frames, without shimming.

    I am replacing the brake cable housing on two older bikes, and have a problem with fit in the cable guides. The bikes are a 1983 Trek and a 1989 Paramount. Both have braze-on cable guides on the top tube. Both bikes came to me with non-original housings - and both were 5 mm, but they fit very loose in the guides, so they allow the housing to move too much. I use sidepull brakes, so the housings need to be snug at the rear guide near the seat. I have some 30-year old 6mm housing which fits pretty good and snug in the Trek, but will not even fit into the Paramount guides. I don't have enough of this old housing to do either bike.

    Outside of using some ulgy means to hold the housing in place, I am looking for suggestions.

    Here are some photos - the Trek is the yellow frame.
    Attached Images Attached Images

  2. #2
    Senior Member Retro Grouch's Avatar
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    QBP has 5.5mm "stainless look" cable housing listed in their catalogue. They say that it's kevlar reinforced, 15% lighter, and useful for both brakes and derailleurs. It's about 4X the cost. I've just told you everything that I know about it.

  3. #3
    Senior Member Thrifty1's Avatar
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    How about cable housing end ferrules......

  4. #4
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    My '83 Trek has top tube cable guides for the rear brake but the housing is one piece and runs from the handlebar lever all the way back to the brake adjusting thimble with no bare wire exposed. The housing is a slight slip fit in the guides but it makes no difference due to the way it's configured.

  5. #5
    JRA...
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    i'm not sure i understand the problem, the pictures show cable/housing guides, not housing stops. shouldn't really matter unless you're using some odd brake that won't accept 5 mm housing, which i've yet to see on bikes or brakes obvious spec'd with 6 mm housing. a little loose is far better than having to shove housing through a guide that's tight. is it creeping towards the bars and not shifting back or something?

  6. #6
    RidesOldTrek
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    Hillrider, mine is the same - maybe I wasn't clear about that. The 5 mm cable housing is very loose in the guides, and the rear brake doesn't work evenly as a result. Sidepull brakes really need to have the housing anchored or restrained fairly close to the brake, since they depend on the combined cable and housing forces to operate correctly. If the housing moves back unrestricted, the caliper pressure is uneven. The front housings are short enough that they work properly with the standard front setup.

    I will probably end up using an old fashioned housing clamp or tie-wrap at the last guide (ughh!) or shim it with something at the last guide so it doesn't move. Maybe this is one reason this method of housing guide isn't used anymore?

    Thanks for your input.

  7. #7
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    Sidepull brakes work by anchoring the housing at the brake lever and at the adjusting thimble on the caliper arm. What happens in between should make little difference as long as the housing is one piece. Remember the old "pre-aero" brake levers? The housing was free to flop around for a significant length between the lever and the first frame guide and the brakes worked fine.

    If you want to anchor slightly undersize housing in your current top tube guides you could build up "arbors" of electrical tape by winding a couple of turns around the housing at the guide locations. Use just enough wraps to get a snug fit and nothing should move.

  8. #8
    RidesOldTrek
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    Quote Originally Posted by HillRider
    Sidepull brakes work by anchoring the housing at the brake lever and at the adjusting thimble on the caliper arm. What happens in between should make little difference as long as the housing is one piece. Remember the old "pre-aero" brake levers? The housing was free to flop around for a significant length between the lever and the first frame guide and the brakes worked fine.

    If you want to anchor slightly undersize housing in your current top tube guides you could build up "arbors" of electrical tape by winding a couple of turns around the housing at the guide locations. Use just enough wraps to get a snug fit and nothing should move.
    My first thought was to build up the housing as you suggest, and it's probably what I'll do, only need to do the last one. I disagree on the sidepull issue, though. On those old pre-aero levers, which I still use, the cable housing was nearly always anchored by the cable clips, or used a system similar to current designs, where the cable was open for much of the top tube, and housing stops were used. You're right that it doesn't matter what happens up near the lever, but it does matter what happens back at the caliper. The housing must exert some force against the caliper for the brake to work. If it slides back toward the handlebars and flops around, it creates it's own expansion loop, and become ineffective.

  9. #9
    JRA...
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    Using that logic, if you slide the housing away from levers without return springs, they should go slack. they don't. Cable and housing transmit force by putting the housing in compression along its length, whether or not stops are involved. All clips and guides do is keep things tidy. In fact, if you let the housing flop all over the place, you may find that the brakes rub the rim, as the housing actually lengthens a little when you bend it.

  10. #10
    RidesOldTrek
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    Quote Originally Posted by dafydd
    Using that logic, if you slide the housing away from levers without return springs, they should go slack. they don't. Cable and housing transmit force by putting the housing in compression along its length, whether or not stops are involved. All clips and guides do is keep things tidy. In fact, if you let the housing flop all over the place, you may find that the brakes rub the rim, as the housing actually lengthens a little when you bend it.
    Look at Sheldon Brown's article on cable length - it illustrates exactly what I am talking about, with a series of three photos:
    http://www.sheldonbrown.com/cables.html

    If the housing was left to move around as much as it wanted to, you could have all three of the conditions he illustrates in his photos with the same length cable, and his point would be moot. I experienced exactly what he shows in his photos. When the cable housing position is like his "too short" photo, the brake caliper with the cable anchor bolt moves to the rim first. With a sloppy fit of the housing in the guides, even if you start out with the cable in the "too long" position, over a short time the housing ends up in the "too short" condition and stays that way.

  11. #11
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    Mostly what Sheldon is trying to do is reduce cable/housing friction by keeping the housing as short as possible and insuring any bends are smooth.

    You can prevent the cable housing from moving around as his illustrations show by building up the outside diameter with a tape wrap as I mentioned above. That's all you need to do.

  12. #12
    Senior Member juicemouse's Avatar
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    Quote Originally Posted by ridesoldtrek
    Look at Sheldon Brown's article on cable length - it illustrates exactly what I am talking about, with a series of three photos:
    http://www.sheldonbrown.com/cables.html

    If the housing was left to move around as much as it wanted to, you could have all three of the conditions he illustrates in his photos with the same length cable, and his point would be moot. I experienced exactly what he shows in his photos. When the cable housing position is like his "too short" photo, the brake caliper with the cable anchor bolt moves to the rim first. With a sloppy fit of the housing in the guides, even if you start out with the cable in the "too long" position, over a short time the housing ends up in the "too short" condition and stays that way.
    One of my bikes exhibits the same thing that I think you're describing. The rear brake cable is routed internally and the housing is free to slide back and forth within the top tube. I ended up cutting the housing a little too short, so that whenever I turn my bars very far to the right, the housing gets pulled towards the front of the bike and becomes taught at the back (see second picture) and stays that way. I have a feeling this wouldn't happen at all if the housing were longer, so that's what I'm going to do the next time I replace my cables/housings. But even when the housing is being pulled towards the front of the bike, the braking is completely unaffected besides maybe a little extra friction. The brakes engage with the same amount of lever travel.

    Maybe older sidepulls behave differently than modern dual-pivot sidepulls, but I can't imagine how. I think your problem could be resolved by lengthening your housing, or by simply using a zip-tie around just the housing ahead of one of the cable guides to prevent it from going through.
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  13. #13
    RidesOldTrek
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    Thanks to everybody for their input.

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