Linear Pull Brake Service
This article will discuss linear pull style brake rim calipers. Caliper attachment to the frame, pad adjustment to the rim, and pad centering and clearance will be reviewed.
Linear pull brakes are a variation of “cantilever brakes.” Each arm pivots on a frame fitting called a “braze-on.” Like cantilevers, the pivots are located below the rim. The cable housing attaches to one arm at a linkage and “noodle”. The bare cable continues to a pinch bolt on the other arm. Pulling the cable then pulls the arms and brake pads to the rim.
The linear pull brakes mount to the same frame fittings as the cantilever brake. The outside of this surface should get some grease to help them run smooth and not blind. The recommended thread treatment is a mild thread locker. Install the thread locker inside the thread of the fitting.
The brake calipers have a spring that will insert into one of three possible frame/fork mount fittings. The top-most fitting provides a lot of spring tension. Typically, select the middle hole and make sure that both sides are symmetrical and in the same middle hole.
Mounting bolts are now threaded into each side. If there is pre-installed threadlocker on the bolt, it is normal to feel a little resistance as it threads in. A typical torque for the mounting bolts is 8 to 10 Nm. The arms should still swing freely after tightening the mounting bolt.
The common linear pull will have a threaded stud system. There’s a series of convex and concave washers that create a ball and socket system. This will allow for alignment on several planes: it will allow for toe, it will allow the vertical face of the pad to be square to the rim, we can move up and down in our brake arm for height. Everything is secured with a single nut at the back of the brake stud.
Brake pads 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: Linear pull pads should be set to the top edge of the rim braking surface, but never so high the pads would touch the tire. The linear pull the arms toward the rim on an arc coming down as they approach the rim. As the pads wear and thin, they tend to travel further down the braking surface of the rim. Beginning as high as safely possible allows for more wear as the pad thins.
TANGENT: This is the setting of the pad tilt. Viewed 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.
“Toe” is an adjustment that can help reduce squealing. Loosen the nut and bring the wrench forward or back as needed to change toe to the rim.
A second useful technique to get some toe is to put a shim at the back edge of the pad. Align the pad fully to the rim, secure the nut and remove the shim. Even a rubber band can act as that shim. Secure the pad fully, remove the shim, and there should be a slight gap at the back from the shim. Repeat the process on the other side. (IMAGE)
Before setting pads, begin by double-checking that the wheel is adequately centered in the frame. If the wheel is moved from current position, pad alignment will be affected.
- Loosen pad nut/bolt and lubricate curved washers and thread. Adjust one pad to the rim at a time.
- If desired, install rubber band shim at back edge of pad. This helps to set the toe.
- Push the caliper arm to the rim and view pad alignment. Align pad correctly in four positions.
- Set the pad’s vertical height on rim braking surface.
- Set the pad’s vertical face to be parallel to the rim’s face
- Set front and back edge of the pad to be level to the rim, so it is tangent to the rim.
- If toeing with a shim, set it so the front edge and back edge with rubber band should be touching the rim at same time.
- Tighten pad nut and remove rubber band. Inspect pad alignment again.
- Repeat alignment of other pad.
The brake cable housing will be stopped at the “noodle”. The linkage (noodle) holds the housing and the cable passes out to the other arm. This is a common place to get a lot of moisture and corrosion - consequently, lubricate inside the liner of the noodle.
With the housing fully secure in the noodle, the noodle is secured and seated in the linkage, draw the arms to the rim. Use a “fourth hand” such as the BT-2. Don’t squeeze the tool with force. Pull slack out of the system. Pull pad to the rim and secure the pinch bolt.
Pull the lever with force to test the pinch bolt holding the cable, and to settle in the housing. Set the pad clearance at the rim by the feel at the lever. If the pads are too tight, the lever is going to pull and immediately engage. That is simply too close. If the wheel comes out of true at all, it’s going to rub the pads. Additionally, it really doesn’t give us good braking power. Third problem - it’s difficult to disengage the quick release mechanism. We should be able to pull out the linkage from the noodle, and here we are having trouble doing that. This brake is set too tight.
Here, we’ll bring the barrel adjuster in toward the lever, giving us more slack. Here we have more travel - that’s good for our leverage at the hand. We are well greater than an inch clearance when we’re contacting, so we have plenty of brake power and here we can disengage and reengage our quick release easily. This brake is not too loose, it is not too tight, we would set the rear brake the same way. It’s time now to center the brakes.
Inspect the pad centering to rim. Use a set screw on sides of caliper to center pads to rim. Tighten the set screw on the arm with pad that is closest to rim. The centering screw increase the return spring tension when tightened. Loosening a centering screw relaxes the spring and this move the arm closer to the rim. Inspect that pads are not rubbing tire. Readjust if necessary. Clean the rim surface and test ride bike.
Trim the cable and install the cable end cap.