Hydraulic disc brakes (which pretty much all of our bikes come with) work a little differently than cable brakes, which you may find more familiar as they often come on road bikes and mountain bikes of years past. While the cable brake is much simpler to service, the hydraulic brake offers a lot more power and consistency of braking power over the long term.
There are 7 main components of each hydraulic brake on the bikes we sell. We defined each component below and added what to watch out for when it comes to service and replacement:
1. Brake pads: It’s impossible to put an accurate mileage interval on when your brake pads need to be replaced since it depends on so many factors, but about every 2,000 miles for a non-cargo bike and every 1,200 miles for a cargo bike is a safe rule of thumb.
2. Brake fluid: The fluid should be checked and/or burped or bled whenever replacing a set of pads or a rotor or whenever the pressure in the brake lever feels soft. Fluid can break down over time and at that point, lose its ability to hold pressure.
While this isn’t something you should necessarily know how to do at home, it’s a good rule of thumb to know the type of brake fluid your brakes require, so when it comes time to bring your eBike in, you can confirm with your mechanic.
There are a few different types of hydraulic brake fluid: Tektro and Shimano use red mineral oil, while Magura uses blue mineral oil. SRAM and Hayes use Dot fluid of various types.
Important: As with any brake system, it is of the utmost importance to not rely on word-of-mouth but rather consult the manufacturer directly regarding compatible fluids if you’re unsure.
3. The rotor: The rotor is the metal disc on each wheel that the brake pads and caliper squeeze in order to slow the bike down and to stop. It is critical that the rotor is in good condition to prevent loss of braking performance.
Common threats to rotors include contaminants, such as motor oil on a city street that gets picked up during a rainstorm; regular wear, which happens over time from the brake pads biting at the rotor and can also be exacerbated by a caliper that is out of alignment and dragging on the rotor; certain scenarios, such as riding off-road, when the rotor should be checked periodically to make sure it’s not getting impacted by rocks, gravel, etc.
When rotors should be replaced: If they develop a step or lip in the surface, indicating that it is starting to get gouged out. Another sign to look out for is if you see a purple iridescent surface where the brake pads hit the rotor, it’s likely time to replace it.
Warning
Remember to consult each manufacturer’s guide individually to determine minimum thickness thresholds in millimeters for each brake rotor. Also, keep in mind some rotors of a lower quality are specified for “resin pads only” and will present a potentially dangerous scenario if used with metallic pads, which are made of a much harder material, and will cause the rotor to wear out early or fail.
Otherwise, if your rotor has no lip, or burned surface and is still above the minimum thickness specified by the manufacturer, you are good to keep rolling. In this case, just wipe the rotor down with rubbing alcohol to clean the surface and refresh it, and clear off any grime or grit that would affect the brake’s performance.
4. Brake lever (also known as the master cylinder assembly): The brake lever consists of two parts: a lever blade, the part that sticks out from the grip, that you rest your fingers on and pull, and a piston (that isn’t really visible) inside the brake lever housing, which is called a master cylinder or primary cylinder. When the brake lever blade is pulled, it activates your brake system by pushing in the master cylinder piston, which in turn compresses the hydraulic fluid contained inside. The master cylinder converts the force of your fingers pulling the lever blade(s) into hydraulic pressure.
If you ever drop your bike on its side, make sure to check the lever, as this is one of the most common causes of a blown seal on a master cylinder (and could also cause a blown seal further down the line on the caliper, too), which would then require replacement. And if your brake lever feels soft suddenly, it is a sure sign that your brakes need service.
Most hydraulic brake levers have an easy-to-access “free stroke lever adjustment” knob or adjustment screw which allows you to adjust the distance from the grip to the lever to accommodate smaller or larger hands. This is also an easy way to cheat more stopping power out of your brake system in the short term, however, in the long term you cannot just increase the distance from the grip to the lever, you must service the pads, rotor, and fluids.
5. Brake caliper: Calipers, which are located by the brake disc, is usually an unnoticed part of the whole brake system. They can sometimes develop leaks in the seals, but that is uncommon if the bike is well maintained, and they mostly stay out of the way. They do require pad changes periodically, as well as realignment.
6. Brake hoses: The brake hoses, the delivery mechanism of the brake system, are pressurized and depressurized when you squeeze the brake levers. The master cylinder pressurizes the fluid, which then travels through the hose with considerable force to the caliper, where the pistons are pressurized to apply braking force from the brake pads to the rotor.
As important as they are, brake hoses are often an afterthought because they don’t develop many issues, but they should be given consideration during certain situations.
The most important thing to keep in mind is to handle the hoses correctly: Don’t yank on them, and try not to snag them on anything. For example, be mindful of the hoses when riding off-road or loading your bike into a car.
When setting up the bike or a new brake, make sure the hoses are routed in a way that will not cause problems in the long term. You should be able to turn the handlebars left and right freely without any cables resisting those movements.
7. Seals, o-rings, and hydraulic fittings: These components are almost unseen to the naked eye, but are integral to holding the pressure inside the master cylinder, hose, and brake caliper. Without these seals, o-rings, and fittings, the system wouldn’t work and would leak constantly.
On older brake systems, manufacturers used to recommend overhauling calipers and master cylinders with fresh seals, o-rings and fittings in order to keep the bike maintained. However, in today’s world, the standard practice is to replace whichever component has a failed seal, be it the master cylinder, the hose, or the caliper.