Cantilever Brake Service
Useful Tools and Supplies
- Repair Stand, holds bike secure for easy work.
- Hex wrenches (commonly 5mm)
- Cable cutter, Park Tool CN-10
- Metric wrench, commonly 10mm CBW-1
- Grease PPL-1
Properly adjusted brake systems require attention to small details. This article will begin by discussing the brake lever, inner wire fitting at the lever, and brake housing. Caliper attachment to the frame, pad adjustment to the rim, and pad centering and clearance are then reviewed. See also related articles:
The cantilever caliper rim brake was once common on MTB bikes, but has been replaced in popularity by a similar brake, the "Linear Pull" type. Cantilever calipers attach to separate frame pivots on either side of the wheel. The inner-wire attaches to a carrier piece located above the tire. The carrier is pulled upward causing the caliper arms to swing inward.
Hand Lever Position
Cantilever rim brakes rely on hand pressure at the brake levers being transferred to the brake pads and the rim. Begin any adjustments by making sure the brake levers are positioned so they are easy and comfortable to reach. Rotate the lever so it is in line with the rider 's arm, making it comfortable to reach and use.
MTB levers commonly have a setscrew on the lever body that allows the lever to be set closer to the grip. The lever reach can then be set according to the rider 's hand size and riding style. Tighten the reach setscrews and bring the levers toward the grip to accommodate smaller hands or shorter fingers.
The cable system connects the brake lever to the caliper at the wheel. The brake inner-wire has a fitting on one end, which sits in the lever. Upright bar levers use a round disc shaped end about 7mm in diameter.
The inner-wire passes through brake housing, which allows the inner-wire to connect from the levers to housing stops on the frame. Housing also allows for bends around corners on the way to the brake caliper. Housing should be neither too long nor too short. For more detail on brake housing and housing length, see
Cantilever caliper arms are attached to the frame or fork at the "braze-on". The braze-on is a 8mm diameter, 16mm long stud fitted to the frame.
Some models of cantilevers have removable return springs. Each side uses a different coil spring direction. If springs are reversed, they may become damaged, and the brake will not operate properly. As seen from the mechanics view (as in the image below), the right caliper arm uses a right-hand coiled spring. The left caliper arm uses a left-hand coiled spring.
This right-side braze-on uses a right-hand spring. Coils will contract when brake caliper is moved toward rim.
Additionally, some caliper arms have multiple spring-hole options for spring placement inside the arm. Mount springs into symmetrical holes for left and right calipers. The spring holes will allow you to change spring tension.
When installing calipers, grease springs and the braze-on before installing the caliper. The braze-on may have different spring hole options. It is typically best to choose the middle hole.
Mount and secure the brake calipers to the braze-ons. Use care not to over-tighten the mounting bolt. Generally, about 30 inch-pounds is adequate for cantilever caliper mounting bolts.
Brake pads attached to cantilever caliper arms and move to press on the rim braking surface. The pads do not move straight in toward the rim, but swing on an arc. This means the pads actually move downward as they move inward. Pad alignment to the rim is very critical to brake performance.
Brake caliper adjustments depend upon the wheel being adequately centered in the frame. A miss-aligned wheel will affect both pad centering and pad placement on the rim. Realign the wheel before beginning pad adjustments. The front wheel seen below is off to the viewer's right. Open the quick release skewer and adjust wheel centering before proceeding with caliper adjustments.
Brake pads are typically adjustable in several directions. The pad should be correctly adjusted for vertical height alignment, tangent alignment, vertical face alignment and pad toe. Not every brand or model of brake caliper has every adjustment, and sometimes you must simply compromise when setting pads.
- Vertical Height Alignment:
- This is the setting up and down on the rim-braking surface. View caliper face-on and move the arms, watching the pads move to the rim. Set the pad to the upper edge of the rim-braking surface, but never above the braking surface. As the pad wears thinner, it tends to move down on the rim braking surface.
Set height to top of braking surface.
- Tangent Alignment:
- This is the setting of the pad tilt. Viewed pad from the side, the front and back of the pad should be level to the rim. One side should not be higher or lower than the other side. Use care when tightening the pad fixing bolt and hold the brake pad to keep it from twisting.
- Vertical Face Alignment:
- This is the setting of the pad vertical surface relative to the rim vertical surface. The vertical face of the pad should be set parallel to the face of the braking surface.
- Pad Toeing:
- This is the setting of pad angle as it touches the rim. Toeing refers to setting the pad so the pad's front edge strikes first, which tends to reduce squeal during braking. Caliper arms tend to have play in the pivots and the arms flex when the brake is applied. This may cause squealing in the brake pads. It is simplest to first ride the bike and see if the brakes squeal.
Most models of cantilever calipers use a "smooth stud brake pad." The brake pad is fitted with a non-threaded stud. The stud fits into a hole in a bolt head that secures to the caliper arm with a series of convex and concave washer and spacers. This system allows the pad face to adjusted to correct positions described above. Generally, it is easiest to adjust brake pads after the caliper arms are correctly positioned. The brake pads may prevent this. Loosen brake pad-fixing nuts on both sides of cantilever and lubricate threads, curved washers and washer-to-arm contact points.
Cantilever Adjustment Procedure
- Turn brake lever barrel adjuster fully clockwise into lever body, then unthread six or eight complete turns.
- Position caliper arm straddle wire. For straddle wire cable carriers using pinch bolt, this unit should be placed as low as practical. The bottom of the carrier should be approximately even with the lowest part of the rear seat stay bridge or front fork crown.
- Fully secure pinch bolt of straddle wire carrier. The wire will become flattened by bolt. It can be awkward to hold carrier while tightening nut. Use an open end wrench on head of bolt. Hold so wrench opening is in line with cable.
- For brakes using a "link unit", check the primary wire is correctly routed in link unit.
- Pull primary wire through wire pinch bolt until lower section of caliper arms appear to be approximately parallel to one another. View area of caliper from frame mounting bolt to brake pad bolt. Consider this a line, and adjust brake calipers in and out until these lines are close to parallel.
Note: Using a fourth hand tool (Park Tool BT-2) can make this procedure easier. Place tool on the cable about one inch (2.5cm)from caliper arm. Squeeze tool handle to grab cable and push against caliper arm. Loosen pinch bolt. To shorten wire, squeeze handle. To relax wire, relax handles.The caliper below was set so the arms are too far inward. The brake pads are not rubbing. When the straddle wire pulls, the arms will not be able to apply force to the pads and to the rims. In this case, loose the straddle wire, and reset pads more inward on both sides.
- View centering of caliper arms to rim. Do not be concerned about pad centering at this time, only caliper arm centering. Most models of cantilever brakes use a centering set-screw on caliper arm to center. Turning set screw changes spring tension in that arm. For example, to move both arms right, turn right side set screw clockwise. To move both arms left, loosen screw counter-clockwise. Squeeze lever to work calipers and check centering again. Caliper arms should be centered to rim.
- Attach rubber band around backside of pad. This is used in pad alignment only and is later removed. The rubber band creates a shim to give "toe "to brake pad. If it is difficult to mount the rubber band, remove one pad at a time from the caliper. Note pad orientation in mounting bolts, especially order of washers and spacers.
- Re-install pad into pad fixing bolt and adjust only one pad at a time for correct alignment to rim. Push pad until it is touching rim, but do not push caliper toward rim. Align pad correctly in four positions as describe in Pad Adjustment above. View pad alignment from top, beneath, front and side.
- Hold mounting bolt with hex wrench, and tighten mounting nut. Pad should be touching rim after adjustment. Tighten nut to about 70-inch pounds torque. This is about a 20 pound effort if you are holding thewrench three inches from the nut.
- Vertical face-parallel to rim face.
- Tangent-front and back edge of pad should be level to rim.
- Height-close to top edge of rim ,but never above.
- Toe-slight gap at back (rubber band will hold back edge out).
- Remove rubber band from rear and view toe. There should be a slight gap at back of pad. Pad should be slightly rubbing rim at this time.
- Loosen other pad, install toeing rubber band, and repeat adjusts as with first pad.
- Both pads should be touching rim when pad adjustment is completed.
- Squeeze lever multiple times to seat inner-wire and test inner-wire pinch bolt. Cable should not slip.
- Set clearance at lever for rider preference. If brake feels tight, turn barrel adjuster clockwise to loosen inner-wire tension. If brake feels too loose, turn barrel adjuster counter-clockwise to tighten inner-wire tension. If barrel adjuster is all the way engaged at lever and brake lever is still too tight, loosen inner- wire pinch bolt and allow slack to feed through pinch plate. Tighten pinch bolt and test again. Use adjusting barrel at lever to set to preference.
- View pad centering to rim. If not adequately centered, use centering set screw on caliper arm. Tightening screw increases spring tension, which pulls arms to side of set-screw. Loosening the set-screw allows the arms to move away from the set-srew side.
- Inspect that pads are not rubbing tire. Re-adjust if necessary. Use care not to move brake pad stud in or out from caliper arm as this changes centering. Move pads only up/down, rotate, or twist as necessary.
- Vertical face-parallel to rim face.
It is not important that the brake pads strike the rim at the same time. It is more critical that pads have symmetrical clearance when full open.
Some brands and models of cantilever calipers have no centering setscrew or other system of centering. In this case move pads laterally as necessary in pad fixing bolts. Changes to spring tension at the braze-on is drastic, and typically will not solve alignment problems. Some brands use adjustable spring tension on each caliper at the mounting bolt. Spring tension can be changed on either arm.
Pads will wear out with use and require replacement. Pads will also harden and become ineffective with age. Pads may also become embedded with aluminum or other contaminants. Inspect and remove as necessary. Pads that are aligned too low on a rim will tend to develop a lip on the low edge. This lip makes correct alignment impossible.