Direct-Pull Cantilever Brakes

Direct-Pull Cantilever Brakes

by Sheldon "Stop!" Brown


Direct Pull Cantilever Brake

Direct-pull vs Traditional Cantilever Brakes

Traditional cantilever brakes used two cables, a main cable running down the centerline of the bike, and a second, "transverse" cable connecting the cantilever units on each side of the wheel. The main cable would pull upward on the middle of the transverse cable, causing the cantilever untis to rotate inward. The "direct pull" cantilever, also commonly known under it's Shimano trademark name "V-Brake" is a simpler design, using only a single cable. The cable housing connects to one arm, the inner cable runs across the top of the tire to the opposite arm. When the brake is applied, the housing pushes on on cantilever while the inner cable pulls the other.
Since the cable runs straight across the top of the tire, direct pull cantis need longer arms to get the cable high enough to clear the tire. This increases the Mechanical Advantage of the system, requiring the use of special matching brake levers
 

Quick Release

DESCRIPTION DESCRIPTION DESCRIPTION
Normal PositionBoot Pulled AwayNoodle Unhooked
For wheel removal, the noodle may be unhooked from the arm link. This will allow the brake shoes to open up wide enough to clear even a fat tire. First, pull the boot away from the end of the noodle. Then squeeze the brake arms together with one hand while unhooking the lower end of the noodle from the keyhole-shaped slot in the arm link. Make sure to hook the brake back up immediately after you re-install the wheel!
 

Cable Issues

Most brake problems are not caused by poor setup, not by poor quality brakes, but result from excessive friction or poor installation of the cables. See my article on cables for tips on this topic.

Cable Adjustment

The most basic brake adjustment is the cable length adjustment. On properly equipped bicycles, fine adjustments may be made without any tools, by turning an adjusting barrel at the end of a length of cable housing. The adjusting barrel for a direct-pull cantilever brake is normally located on the hand-lever, where the housing exits.
Adjusting barrel

Reach Adjustment

Many brakes intended for upright handlbars feature a reach adjustment, usually a screw or cam. This sets the rest position, and is mainly used to bring the brake lever in closer to the handlebar for easier operation by a rider with short fingers. This adjustment should be as loose as allows convenient gripping of the lever, because if you bring the rest position of the lever in too close to the handlebar, you increase the risk of having the lever bottom out against the bar. If you change the reach adjustment, you should expect to have to change the cable adjustment as well.
 

Shoe Adjustment

Brake shoes can be adjusted in 5 different directions:
  • Height

    This is the most critical adjustment. The shoe should contact the rim fully, but not overlap it. If the shoe is set too high, it will rub on the tire, destroying it very quickly. If the shoe is set too low, it can "dive" under the rim and get caught in the spokes, leading to dangerous wheel lockup.
    On mountain bikes with narrow rims and big bulgy tires, it may be quite difficult to get a good vertical adjustment--the shoe may clear the tire when the brake is engaged, but it may rub on the sidewall of the tire in its rest position.
    As the brake shoe material wears down, the shoe hits lower and lower on the rim, increasing the risk of "diving" into the spokes, so periodic checking is in order.
  • Roll angle

    The roll angle should be set so that the shoe hits the rim squarely, both the top and bottom of the shoe should meet the rim. If this is not set perfectly, normal pad wear will eventually even it out, but braking will be less effective until the shoe has worn in.
  • Pitch angle

    The pitch angle should be set so that the shoe follows the curvature of the rim as closeley as possible.
  • Yaw angle ("toe in")

    The shoe can be set so that the front edge of the shoe contacts the rim slightly before the rear edge. This is commonly called "toe in." If this is not set perfectly, normal pad wear will eventually even it out, but braking will be less effective, and the brakes may squeal until the shoe has worn in. Most direct-pull cantilevers, however, use asymmetrical shoes (longer end faces the rear) that are designed to be set with no toe in.
  • Extension

    Extension is the adjustment of the distance from the pad braking surface to the cantilever arm. Direct pull cantis aren't very critical about this, as long as there's a reasonable distance betwen the tops of the arms.

    Shoe Attachment Hardware

    There are two different ways of attaching brake shoes to the cantilever arms, threaded studs or smooth studs with eye bolts.

    Smooth Stud

    Brake shoe with smooth stud

    Threaded Stud

    Brake shoe with threaded stud

    Threaded-stud brake shoes with plain washers generally offer height and pitch angle adjustability but little else. For this reason, they are not suitable for direct-pull brakes. Most direct-pull cantilevers use threaded-stud brake shoes with spherical (domed) washers that allow for all angle adjustments. There are two convex washers, which go inside and outside the arm, and two matching concave washers that mate with the convex ones.
    Usually, the concave washers are two different thicknesses, so you can select two different "extensions" depending on whether you put the thick or thin concave washer on the inside. Smooth-stud brake shoes are the type most often used on traditional center-pull cantilevers, though a few direct-pull units do use them. With modern cantilevers, they permit 5-way adjustment. Older cantilevers, such as the classic Mafacs didn't have any provision for yaw angle (toe-in) adjustment, but most cantilevers made since the 1970s have provided all 5 types of adjustability.
    Sometimes it is difficult to get all 5 adjustments set at once, and to get the bolt tight enough without twisting it out of position. It helps if you remove the nut from the bolt and lubricate the threads.
    With most direct-pull cantis, you can unhook the spring from the back of the arm, and this usually makes it a lot easier to set the brake shoe position.
     

    Squealing/Squeaking

    Squealing brakes is a common problem, and there's no one simple solution to it.It's caused by the friction of the brakes against the rim flexing the brake arms, which then slip back, grab, slip back, grab, etc. This process happens at such high speed that it often causes an audible vibration.
    All brakes do this, but with luck the pitch (frequency) is too high for human hearing.
    This is generally annoying, but not a safety issue. Unlike automotive brakes, bicycle brakes that squeal are usually in good functional condition.
    Here are some things to try if your brakes squeal:
    • "Toe in" the brake shoes, so that the front edge of the shoe hits the rim slightly before the rear edge.
    • Clean the rims with a good, oil-free solvent (citrus, alcohol, something like that.)
    • If the pivots of your brakes are adjustable, make sure that you've eliminated as much play as possible without causing them to bind.
    • Different brake shoes may help. I particularly recommend Kool Stop salmon colored units.
    • A "brake booster" may help. This is a horseshoe-shaped arch that connects the two cantilever bolts together, making the whole system more rigid.
    • If your brakes use the Parallel-Push linkage, the pivots may need servicing. There are special kist for this.
     

    Centering Adjustment

    When the brake is released, the brake shoes retract away from the rim. Ideally, the shoes on both sides should back off by the same amount. If they don't, the brake is not properly centered. In extreme cases, one of the shoes may not retract, and may rub on the rim even when the brake is not being applied. If a brake appears off-center, check first that the wheel is installed straight in the frame/fork. If the wheel is crooked, and you maladjust the brake to compensate, you are creating two problems where there was only one before.

    Spring Adjustment

    If your wheels are centered, and your brakes are not, and, if the pivots are properly lubricated and free-moving, the brake shoes should be centered. If they are not, you probably need to adjust the spring tension on one or both of the cantilevers. Most direct-pull cantilevers have adjustable spring tension. The adjustment will be a small screw with the head facint outward to the side of the bike. The screws are generally located near the bottom of the cantilever, below the pivot point. Sometimes they work with a Phillips screwdriver, other times a small Allen wrench may be needed.
    DESCRIPTION

    Tightening this screw tightens the spring, so you want to tighten the spring of whichever arm is too close to the rim. This will make it spring back farther.

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