Hydraulic disc brakes are nearly ubiquitous on all but the least expensive road bikes. DIY home mechanics fear not: keeping hydraulic disc brakes tuned for optimal performance is not complicated, and it’s likely you already own a few of the tools needed for disc brake maintenance.
While some road bike brake upkeep tips may also work for mechanical rim or disc brakes, the adjustment process for hydro brakes is slightly different. For instance, hydraulic disc brakes self-adjust for pad wear, so there’s no need to mess with barrel adjusters. Also, disc brake fluid is not compressible, so you’ll never need to pre-stretch brake lines after installation.
Silencing squealing disc brakes
The most common issue with hydro disc brakes is noise while braking. Shrieking disc brakes may be a result of the environment (wet conditions), dirty brake pads or rotors, or misaligned calipers. Fortunately, cleaning to silence hydro disc brake components is usually easy and inexpensive. And you can clean rotors without removing them from the wheels.
Using a clean, soft rag that won’t mar the rotor braking surface, wipe the rotors with brake cleaning fluid or rubbing alcohol. To be extra sure that your rotors run quiet and are clean, you can use a flame to scorch the rotor braking surface.
Cleaning disc brake pads is a similar process to cleaning brake rotors with one easy additional step. After removing the brake pads, use 120 grit sandpaper in a sanding block to remove any dirt from brake pads. Thoroughly wipe the pads with isopropyl alcohol, which is less expensive than commercial brake cleaning solution. Ensure the brake pads are free of contaminants by using a flame to scorch the pads' braking surfaces. This is a good opportunity to inspect brake pads for any defects like grooves, and to ensure there is ample pad material before reinstalling the pads into the brake caliper.
Another cause of squealing disc brakes may be improperly aligned brake calipers. To rectify this, loosen–but do not remove–the brake caliper on the bike frame mounting points. While squeezing the brake lever to engage the brake pads, tighten the brake caliper mounting bolts using a torque wrench to the torque specified by the caliper manufacturer.
If your brakes still squeal after cleaning the pads and rotors, and also realigning brake calipers, try changing brake pads to a different brand that is compatible with your caliper and brake rotor type.
Replacing hydraulic brake pads
Swapping hydraulic brake pads is a quick and easy fix to ensure optimal brake performance. Replace the pads in-kind to ensure compatibility, or you can use a third party pad to enhance braking performance, extend brake life, or quiet loud braking action. There’s no single rule-of-thumb for pad replacement frequency, which is affected by combined rider and bike weight, riding conditions and parcours, brake pad material and other factors.
Replacing pads in-kind, is straightforward. If going with third-party replacement brake pads (e.g., SwissStop, Absolute Black, etc.) double-check pad compatibility with brake caliper manufacturers. If you’re unsure about pad material, check the brake rotor model number and compare it against the manufacturer recommendation on its web site. Most brake pad web sites have guides to match brake pads to rotors manufacturers’ models.
Because of the differences in brake pad material–organic or resin disc brake pads may make less noise than metallic or sintered brake pads–you can expect slightly different braking performance. If you’re a relatively lighter weight rider and/or don’t ride in a mountainous area, you might consider using organic pads and appropriate rotors.
After you’ve installed replacement pads, you’ll want to bed-in the brake pads before the next ride. This process glazes brake rotors with a very fine layer of brake pad material, which aids in efficient stopping.
Truing disc brake rotors
Just like bicycle wheels, disc brake rotors can come out of alignment and require truing. Although rotors can withstand very high temperatures and compressive forces, they are not designed to take sideways impact loads, and you should never lean your bike supported by a brake rotor. An easy way to check the trueness of a disc rotor: put a white towel on the floor, position your bike above the towel and spin the wheel. Sight along the rotor as it passes through the brake caliper and you should be able to see any wobble in the braking surface. More obvious, tell-tale signs that a brake rotor is out of true are any sounds it makes against brake pads, or feeling a feedback pulse—akin to a wobble—when applying the brakes.
A minor wobble is relatively easy to fix with a rotor truing tool, or a large-jawed adjustable wrench. Err on the side of caution when truing a disc brake rotor: Use a very light hand and just enough force to set the rotor true.
Replacing disc brake rotors
Inspect disc rotors to ensure they are not grooved, grossly out of true, or worn thin. Those who frequently ride in wet conditions or who brake heavily for extended periods of time–like descending mountains–may need to replace disc brake rotors more frequently than those who ride in flat and dry conditions. Or, if you’ve inadvertently leaned your bike against the rotor and it’s bent, it may need to be replaced. Most rotors have a minimum thickness printed on them. Use a caliper measuring tool to verify your rotors meet this standard. Rotors that measure less than the recommended thickness should be replaced. Rotors designed for use with sintered or metallic brake pads may wear more quickly than those designed for organic brake pads; heavier riders may wear rotors faster than lighter riders.
If you need to replace your rotor, consider replacing it in-kind to ensure compatibility, and also use the same size as the ones being replaced to avoid unnecessary caliper adjustment and ensure optimal brake performance.
After replacing the disc brake rotors, make sure to liberally grease the lockring threads or rotor mounting bolts (tightened to torque specification) prior to cinching tight, to make successive maintenance easy. Take extra special care to keep the new rotor clean and completely free of contaminants during the installation process.
Fixing spongy lever feel
Before taking on a full brake bleed to rectify squishy braking action or mushy feel, consider checking brake lever free stroke. Free stroke is the distance the lever moves while braking, before the brake pads engage the brake rotor. As brake pads wear, the gap between the pads and rotors should not increase (another bonus feature of hydraulic disc brakes) and braking feel should not dramatically change.
But sometimes it's necessary to adjust the lever throw distance which impacts the feel of squeezing the lever against the brake pads. Some component manufacturers design brake levers with a free stroke adjustment screw, however, not all brake levers from all manufacturers are designed with this feature. If your brake lever throw does not feel factory-fresh after some use and you do not have a free stroke adjustment, you can try to fix this by doing something that many mechanics caution against: Squeezing the brake lever without the wheel/brake rotor in place.
Squeeze the lever just a little to force the pistons and pads closer together, then replace the wheel and try the brake(s) again. Do this iteratively and with caution, a small amount of squeeze each time. You do not want to squeeze the levers too much and extend the pistons too close together, or you will have to reset the pistons back into the caliper.
If you’ve reset the disc brake pistons and the lever still feels squishy, or you can pull it all the way to the handlebar and still not achieve good braking, it might be time for a full disc brake bleed.
Issue: Pistons not retracting
Over time, the hydraulic brake pistons may collect dirt and not fully retract after releasing brake levers. If your brakes are still loud when not breaking, and if you’ve already verified that your disc brake rotors are true and also centered, you should clean the hydraulic caliper pistons to ensure the retract into the caliper housing when brake levers are released. If that ting ting ting sound of your brake rotors brushing against your brake pads doesn’t go away almost immediately after you release your brake lever, it could be an indication that you may need to clean the pistons that press brake pads against disc rotors.
After carefully removing the brake pads while keeping the braking surface clean of contaminants, gently squeeze the brake levers to expose the pistons. It’s advisable to not fully squeeze your brake levers to fully close the gap between pistons. Holding the brake levers to expose the pistons, wipe the pistons with alcohol to clean them and then let them dry for a few moments.
While still holding the brakes levers to keep the pistons exposed, apply just a few drops of hydraulic brake fluid to the sides of the pistons (ensuring that you use the fluid appropriate for the specific type of brake).Release the brake lever to retract the pistons; you may need to use a flat, plastic tool (either a brake piston tool, or a tire lever) to push the pistons into the caliper body.
Taking special care to keep the brake pads free from contaminants, reinstall them into the brake caliper body. Then, gently work the brake levers to allow the brake fluid to fully lubricate the caliper pistons.
After doing any maintenance on brake calipers, pads, or rotors, and to ensure the calipers are properly aligned and brake pads are set equidistant from the rotor, use a device like the Hayes Feel'r Gauge Disc Brake Alignment Tool. The tool is easy to use — some riders even use it when doing wheel swaps.
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