How to Align a Mechanical Disc Brake on a Bike

How to Align a Mechanical Disc Brake on a Bike


A rubbing or under-performing disc brake can often make a ride frustrating. Regardless of brand and model, this video will help you
align your mechanical disc brakes. Hello Truman with Park Tool here. This video will help you gain the knowledge you need to adjust your mechanical disc brakes. If you have hydraulic disc brakes,
see this other video for pad alignment. Some typical tools you may need for this repair are: appropriate wrenches – this may include: a T25 Torx compatible, three millimeter,
four millimeter, or five millimeter hex wrench. You will also need a torque wrench
or torque driver with appropriate bits. And a cable cutter to trim the cable
and install the end cap. Let’s go over the key components
of the mechanical disc braking system, including the things that distinguish it
from a hydraulic system. The brake is engaged by a brake lever at the handlebars. On a mechanical system, the brake lever pulls a cable,
which runs through housing, down to the brake caliper. The housing can effectively be lengthened
or shortened with the barrel adjuster, which may be found at the lever,
or the caliper, or sometimes not at all This TRP HY/RD caliper uses hydraulics
in the caliper body to move the pads, although it is actuated by the pull of a cable. For the purposes of pad alignment,
it is considered a hydraulic brake. The brake cable actuates a lever arm. Most mechanical caliper designs have one lever arm
that moves only the outer brake pad when actuated. The rotor then flexes over into contact
with the innermost pad. There are also designs that have two lever arms – On these calipers, both pads move evenly into the rotor. We will cover adjustment and alignment
of both in this video. Brake pads consist of braking compound
bonded to a backing plate. The pads will wear with use and it is important
to verify that they have sufficient thickness. Make sure the pad material measures
at least one millimeter thick. If they measure less or look worn, replace them.
See this video for more information. Disc brake calipers secure to the frame or fork with two mounting bolts. The location of these bolts can vary depending on the frame mount standard, but the adjustment procedures are otherwise the same. Disc brake systems are equipped with wide holes
that allow for lateral movement relative to the rotor. These can be found on the caliper body, the frame, or the caliper adapter. Calipers are equipped with pad adjusters
that move the brake pads in or out from the rotor. Some calipers have only one adjuster
that moves the inner pad. While some calipers have both
an inner and outer pad adjuster. Now that we understand the components and their functions in the system, let’s get into the alignment and adjustment process. First, ensure the rotor is properly positioned
by getting the wheel seated all the way in the dropouts. Elevate the bike and spin the wheel. Inspect the rotor. If the rotor shows a lot of lateral movement, it can be
difficult or impossible to adjust the pads to not rub. Replacement is a good option, but some rotor truing
may be possible. See this other video for rotor truing. Turn the barrel adjusters all the way in at the lever and at the caliper. Check that the lever arm is released and in its relaxed position by loosening the cable pinch bolt. This ensures full lever arm travel during braking. Pull the cable tight so it is free of slack,
and tighten the cable pinch bolt. Be careful not to move the lever arm
when tightening the pinch bolt. This is important because the lever arm
only has a small amount of useful motion. As the pads wear, they should be moved closer to the rotor with the adjustments at the caliper. Do not use the barrel adjusters to move pads inward as the pads wear. This will eventually move the lever arm to a position where it is contacting another part of the caliper, preventing the pads from contacting the rotor. The barrel adjusters should only be used to take out cable slack as the cable and housing system settles in. We will first look at single lever arm actuated calipers. In these systems, only the outer pad moves. For those with both inner and outer pad adjustment, begin by loosening the caliper mounting bolts. This allows the caliper to float. Turn the outer pad adjuster all the way out counterclockwise, then back in one full turn.
This leaves room for future adjustment. Turn the inner pad adjuster clockwise until the pads lock against the rotor. Snug the caliper mounting bolts to align the caliper body over the rotor. Full tightening will occur after good pad alignment is confirmed. Loosen the inner and outer adjuster a quarter to a half a turn. Final adjustments for pad rub and mounting bolt tightening will occur at the time shown. If your caliper only has adjustment on the innermost side, again, begin with the caliper mounting bolts loose. Turn the inner pad adjuster all the way in, clockwise then back off about a quarter turn. Pull and hold the brake lever tight, which aligns the caliper body to the rotor. Snug the caliper mounting bolts Release the lever Back off another quarter turn. Final adjustments for pad rub and mounting bolt tightening will occur at the time shown For those with two lever arms on one caliper,
loosen the caliper mounting bolts Turn the inner and outer pad adjusters all the way out Pull and hold the brake lever If the brake lever goes all the way to the grip, release the lever and tighten both pad adjustment screws 1/2 turn. Repeat tightening evenly until pad contact is felt at the lever Snug the caliper mounting bolts to hold the alignment of the caliper body over the rotor. Full tightening will occur after good pad alignment is confirmed. Release the lever. Final adjustments for pad rub and mounting bolt tightening will occur next. These final adjustments apply to all mechanical disc brakes. The end goal is a caliper that is parallel to the rotor, with even gaps on each side, and an adequate lever feel. Even though setting your pads against the rotor should theoretically have aligned the caliper correctly, it’s common for further adjustments to be required. Pull and release the brake lever a few times to check the clearance at the grip. Check that the lever travel feels adequate to slow and stop the bike. Typically the pads should feel like they are contacting the rotor at a minimum of 1/2 the lever travel. Make changes according to rider preference using the pad adjustments, not the barrel adjuster. Spin the wheel and check for pad rub. If there is no pad rub, tighten the pinch bolt and mounting bolts fully Typically about 6 Nm for the mounting bolts and 4 Nm for the pinch bolt. Trim the cable to about 1 inch and install a cap. If the wheel slows quickly or makes rubbing noise, the pads need further adjustment. Inspect the pad alignment. You may need to reorient the bike for a better view. It is helpful to backlight the caliper body using a white piece of paper or material and even shining a light on it. This makes the pad clearance easier to see To achieve proper caliper alignment, it is sometimes necessary to move one or both ends of the caliper body. Loosen a bolt, move the body slightly, and snug the bolt before checking. Keep in mind that making one adjustment may affect others. If pads appear parallel, but there is rubbing,
pad adjustment is necessary. For calipers with inner and outer pad adjustments, loosen the adjuster on the side with pad rub
in quarter-turn increments until it is gone. Recheck the clearance at the lever
and adjust as necessary. For calipers with inner pad adjustment only, the procedure is different. To adjust the outer pad clearance,
loosen one of the mounting bolts, pull the caliper a small amount to the outside,
and then re-snug the bolt. Repeat these steps on the other bolt in order to keep the pads parallel to the rotor. Finish by tightening the pinch bolt and each mounting bolt fully Typically about 6 Nm for the mounting bolts and 4 Nm for the pinch bolt. If you have installed a new brake cable or if the cable has excessive length, cut the cable roughly one inch past the pinch bolt and add an end cap to prevent fraying. The brake is now properly adjusted and ready to test ride. Here are some other considerations that may come into play during this process. As the pads wear you will need to make further adjustments. Tighten the pad adjusters to bring the pads closer to the rotor, instead of threading the barrel adjuster. Move the adjusters evenly in small increments and test at the lever. As your single arm single adjustment calipers wear, you will need to reset the caliper position from scratch. Refer back to the time shown for the process. Dirty or corroded cable and housing can drastically affect the performance of the braking system. Replace these components if necessary. See these videos for more information. It is assumed that frame mounts are correctly machined and squared with the rotor. If not, it may result in the caliper being vertically misaligned. A bike shop will be able to face or machine these mounts with the Park Tool DT-5.2 to improve alignment, as seen in this video. Some manufacturers use a system of mating conical washers. These help to align the vertical face of the pads to the rotors. These washers must be designed into the system and cannot be added to brakes not designed for them. Additionally, if the brakes come with these washers, they must be used. If there are conical washers only on top of the caliper they should remain on top. Thanks for watching! Be sure to check out our other repair help videos to get help with your brakes, derailleurs, chains, cranks, and much more, and subscribe to our channel to get the latest videos from Park Tool