Bicycle Disc Brakes Maintenance


Bicycle brakes went through a lot of changes and inventions throughout the years, one could even say unnecessary changes. Nonetheless, one thing is certain, disc brakes have the most stopping power of all bike brakes ever invented. That’s why we can see them becoming a piece of standard equipment for almost any type of bicycle.

There are two types of disc brakes that we need to differentiate, mechanical and hydraulic disc brakes. They are both using a rotor as a braking surface but the mechanism works differently.

Mechanical vs. Hydraulic Disc Brake

With a mechanical disc brake, a brake cable is used to pull the brake pads and squeeze the rotor to achieve braking. This is the one with less brake force of the two. The brake force is still better than almost any bicycle brake ever invented, however, cable stretching and tension on the brake lever lose a lot of force through the system before it reaches the rotors. That is why mechanical disc brakes are always on the less expensive end of the brake spectrum but in my opinion still a perfectly valid choice for any bike.

Hydraulic disc brake, on the other hand, uses an incompressible oil to push the brakes pads into squeezing the rotors and stop the wheels from spinning. Note that I said, incompressible oil, which means the force transferred through is almost perfect without any loss. That results in needing to apply a much less force on the brake lever with your hand to brake better. Since power transfer from your hand to the rotor is linear, you can more precisely adjust how much braking power you need at any point during a ride. Hydraulic brakes are an advanced type of brake and used to be a bit more expensive. However today, there are cheaper versions even from market-leading brands and I would suggest this as a priority upgrade if you don’t have them.

Why My Disc Brakes Aren’t Braking Properly?

Other than brake pads being worn out, I’ve encountered dozens of reasons for a disc brake not to brake properly. Some of them were simple malfunctions that came from damaged brakes, but most of them were the result of poor installment and even worse maintenance. From searching around, I’ve realized there are lots of terrible posts about disc brake maintenance which left out important notes and mentions. Especially some mistakes during maintenance that are difficult to realize unless you have loads of experience. So I decided to go into detail a bit more with this post.

How Do I Know If My Bike Brake Pads Need Replacing?

A good rule of thumb is replacing your disc brake pads when they are under 1 mm thick. That is a standard for the optimal performance of your brakes.

Make sure you don’t touch the braking surface of the pads with your fingers because the natural oil our skin produces can contaminate them. With that in mind, you will need to take the brake pads out and use some kind of measuring device. I’m always having a Neiko 01401A Electronic Digital Caliper around with my set of tools which is perfect for precisely measuring any small object.

You can use your brake pads for a bit longer if you really need to do so, but remember to check on them regularly. If you get to the metal part you will ruin your rotors and probably damage the pistons which can be quite expensive replacements.

Lubricants And Disc Brakes

I would say the most common reason for well-adjusted brakes not to brake properly is some form of lubricant on the rotor or brake pads. Most of the time people have no clue how it got there and that’s what I was talking about when I mentioned bad articles about this topic. There are numerous ways in which it can happen if you only give it a bit of thought.

First of all, the worst thing you can do for your bike is to wash all of it at once, especially using a pressurized washer or something similar. What happens is 9 times out of 10 it works just fine, but that one time some oil or some other lubricant gets transferred through the water to a rotor or even inside the brake itself where the pads are. If not that then the brake pads get oil from the calipers itself, because in the case of hydraulic brakes the calipers are lubricated from the inside the system. Pressurized washers are good only if you protect the whole rotors and brake calipers while washing the bike. I personally use the Muc Off Set of 2 Disc Brake Cover which you can get from Amazon.

By now you are aware that in case of disc brakes, the bike and the brakes should be washed and maintained separately from each other. Any lubricant or bike protection products you use will damage the brakes. If that isn’t enough, soap formulas can destroy the brake pads as well. Some soap formulas become slippery when they are burnt by the heat that gets generated by braking, acting as a lubricant.

Mechanical Disc Brake Not Braking Properly

Other than damaging disc brakes with lubricants, mechanical disc brakes can brake poorly simply by brake cable stretching. Lower quality brake cables tend to stretch up to 1% in length. 1% might seem little but for a brake cable where precision is measured in tenths of an inch or centimeter. For this reason, I would never suggest getting generic unbranded brake cables as they are often of terrible quality and durability.

Poor cable housing can create issues as well. There are types of brake cable housings that bend on itself when pressure is applied on the brake lever. This happens because the inside diameter of a cable housing is always bigger than the cable diameter. While proper housings are made to hold through that cable tension, cheaper ones usually fail to do so resulting in some additional movement on the lever that doesn’t actually transfer to braking power.

Other common problems with mechanical disc brakes losing braking power:

  • While the brake pads are getting worn out cable tension must constantly be readjusted.
  • Spring that holds the calipers is weakened by improper adjustment(check down below how to properly adjust a mechanical disc brake)

Hydraulic Disc Brake Not Braking Properly

Hydraulic disc brakes are easier to mess up with oil. Simply because the oil is already in the system. A hydraulic hose or brake calipers can leak a bit of oil in time. Although, this rarely happens and is most likely a result of some oil left in the gaps from installment or bleeding process. Otherwise, you would lose some or even all the tension on the brake lever and wouldn’t be able to brake at all.

That brings us to another cause of hydraulic disc brake not braking properly, air getting inside the system.

Sometimes, even if the oil is not leaking anywhere, air can get inside. Air will pass through small gaps and damaged seals more easily than hydraulic liquid. Since the whole point of the hydraulic liquid is to be incompressible, having air bubbles inside is not a good idea. Air is actually one of the most compressible gas mixtures and the result is greatly reduced braking power or even a brake lever completely losing tension.

In both cases, a complete check on the system is required to make sure nothing is damaged, proceded with bleeding and adding missing hydraulic fluid to the system.

This all may sound a bit complicated, but it’s actually a really simple system and in fact much more reliable than mechanical ones.

Why Is My Disc Brake Rubbing The Rotor?

There are two most likely possibilities for a brake pad to rub the rotor.

First would be that the brake calipers are not aligned properly with the rotor. It might be that a brake is not set up on the bike correctly from the factory or bike shop or the bolts could have loosened a bit and the caliper moved. Also, changing the wheel requires a complete realignment of a brake caliper because the axle/hub position is never the same. In this case, check down below on how to align the disc brake calipers or visit a bike mechanic.

The second possibility is a bent rotor. Not as catastrophic as it may seem at the first sight of it. Rotors are easily bent in and out of alignment and you can easily fix that by yourself. Check the down below on how to straighten a bent disc brake rotor.

Other causes might be that the wheel is not inserted in the fork properly in case of a quick-release system. It can even move during the ride, especially on a mountain bike. A wheel axle can be bent or broken, as well, which can put the whole wheel, including the rotor, at an angle.

Bicycle Disc Brakes Sticking

It may happen that your brake pads are too close and they are constantly braking. This happens if you squeeze the brake lever while the rotor is outside the brake caliper, for example, when you take the wheels off while transporting the bike.

Hydraulic brake pistons won’t retract fully if they are pushed too far out from the brake caliper. It can happen by itself, as well, if you keep using brake pads after they are worn out. A good thing to do every time you change the brake pads is to push the pistons back inside before you put the pads back. A Brake Piston Press from Super B is a great tool for this purpose mainly because you can use it over brake pads without damaging them. Also, when taking the wheel off, make sure to insert something clean between brake pads to block them so this won’t happen. Ideally, it’s best to have the original pad spacer for that brake.

How to Adjust Mechanical Disc Brakes

Mechanical disc brakes require constant adjustments as the brake pads are wearing out.

A common mistake I see is people adjusting mechanical disc brakes by increasing tension on the brake cable, either by using adapters on brake levers or the brake itself. That’s how you would normally adjust the mechanical rim brake but this is quite different.

Because of the brake cable only moving one brake pad, this would cause a brake to go out of the center, lowering braking power in the process. Even if the alignment is only slightly out of the center and doesn’t affect braking power, this way you can damage your brake calipers. The outer side brake pad is pushed by a piston on a spring. That spring is tightened by the cable and if the cable tension is set too high the spring breaks in time or simply loses its own tension.

A proper way is to have cable tension set so that it’s at the minimum but still not loose. You can check that by making it a bit loose and then increasing the tension a bit by a bit to see when the “empty” movement on the lever disappears. When that happens that’s the proper cable tension and should be at that point all the time.

What usually happens at that point is too much travel on the brake lever which you need to fix by moving the inner side brake piston closer to the rotor. You can achieve this by using a hex wrench screw on the right side of the brake caliper. When you achieved the proper travel on the brake lever, now you can properly align the brake calipers so the pads don’t scratch on the rotor. At that point, tighten the brake calipers on the frame with the attachment bolts.

That’s the process that should be followed every time and your mechanical disc brakes will have maximum braking power and will last for a very long time. The only thing you would need to change is brake pads when they are worn out.

Brake Cable and Housing Maintenance on Mechanical Disc Brakes

Same like rim brakes, mechanical disc brake braking power can be affected by rusty cables and cable housings. If it has difficulty moving through the housing you will have a hard time pulling the brake lever.

Depending on the climate, in some parts of the world cables and housing last longer than some other. In proximity to salt water, there is a chance that they will last much less if not maintained properly. That’s because winds carry salt particles that cause rust in those areas.

I live in such an area and I can’t even tell you how many people complain about the shift and brake cables going bad in a short time. However, there is a simple solution called lubrication. I’ve even got to the point where I’m recommending lubricating cables to each and every customer that buys a bike at my shop. Otherwise, they would be back in a month or two with this problem no matter how expensive and high quality their bike is.

The tricky part is you have to learn how to adjust the brake to do this properly. You have to take the cable out of the cable housing and pour some lube inside. You can use your regular water dispensers with oil like WD-40 or Muc Off MO94, but I recommend Wet Chain Lube from any brand.

Sometimes, if the cables and housings are already too rusty or completely stuck, this won’t work, or at least not for long. I would always change cables at the first sign of rust if I fail to protect from it. Simply because rust weakens the cable and it can break, which is not something you want happening during a ride.

Good additional protection is having Juscycling Teflon Coated Cables with a protective layer that not only makes them more durable but eases their movement inside the housing. If you decide to buy, make sure to choose the exact ones you need because they offer cables for Mtb brakes, road brakes, and shifters as well.

How to Adjust (Bleed) Hydraulic Disc Brakes

Adjusting hydraulic brakes requires a process called bleeding. It’s a process of inserting oil and extracting air from the hydraulic system at the same time. The hydraulic system, in this case, consists of brake calipers, hydraulic hose, and a brake handle.

It’s not a very difficult process but it requires special tools and a bit of practice and understanding of what you are doing.

In short, there are 2 types of bleeding for bicycle hydraulic brakes. Two-way bleeding and one-way bleeding. Two way bleeding is pushing hydraulic fluid through one side to the other in a stream using two bleeding syringes. Make sure the extracting end is vertically higher than the end you push fluid into. On the other hand, it would cause the oil to pass through the system while the air gets stuck inside.

One way bleeding is pushing in and extracting hydraulic fluid from only a handle or a brake caliper. By doing this you are applying a bit of pressure on the system so you need to make sure that the bleeding syringe is fixed properly to avoid making a mess. You need to achieve a wanted volume of hydraulic fluid so that the brake lever has the desired braking point. In order to extract air in both cases, it’s recommended to have the whole system in a vertical position so that the air bubbles move more easily to the one end. What I like to do is hang the bike upwards on a wall mount, or put a repair stand at an angle.

A detailed explanation of a bleeding process for each and every situation and a potential problem requires a separate article, which I intend to write and link in here soon enough.

How to Adjust Hydraulic Brake Levers

On most hydraulic levers there are tiny hex wrench screws that adjust how far the lever is from the handlebars.

This can be used to adapt levers for the size of your hands. Especially, for one finger levers where you want the lever to be in a bit more precise position for your hand size.

Additionally, on some brakes, these tiny screws can be used to increase the distance from the handlebars as the brake pads wear out. As they wear out travel distance of the lever gets increased but by adjusting the position you can keep that braking point of the lever in the same position. As long as the brake lever doesn’t get out of reach of your fingers.

On a side note, I’ve encountered these screws moving on its own. Especially with lower end brakes, primarily from Tektro. In that case, it may seem like there is something wrong with the brake or the fluid, while actually all you need to do it tighten that screw back into position. I found that using a bit of Loctite Heavy Duty Threadlocker on the screw’s thread goes a long way in preventing it from happening again in the future. Even though, there is already some of it from the factory, however, not enough.

How to Align Disc Brake Calipers

A standard procedure is unscrewing the brake caliper bolts a bit then squeezing the brake lever which should center the calipers on the rotor, and then tighten the brake caliper bolts. This method works, but in my opinion only on better models of hydraulic disc brakes. On others, it doesn’t work more than half of the time.

In these cases, aligning disc brake calipers on a bike can give you some trouble. Mostly when you are not in a situation in which you can easily align them by slowly centering the caliper on each bolt. I found it difficult to do if there is noise or if I’m unable to see between the brake pads easily.

Luckily, there is an amazing tool that isn’t expensive and does wonders in these situations. Hayes Brake Pad & Rotor Alignment Tool is a simple tool that you insert between brake pads and the rotor. It gives enough space to let you tighten the caliper bolts without worries. Afterward, just take the tool out and there should be equal gaps between each brake pad and the rotor.

I’ve had the tool at my bike shop for months and I use it every day when assembling new bikes or servicing used ones and it never failed me if the rotor is straight. Just remember to keep the tool clean from any grease and oil to prevent contamination on brake pads and rotors.

How to Straighten a Bent Disc Brake Rotor

To true the rotor, as we would say it, you need to have it inside the brake caliper so you can see and hear scraping off the brake pads. To straighten the places where the rotor is bent I’m using a simple mid-sized adjustable wrench like this Crescent 12-inch adjustable wrench. It’s not really practical but I’ve got used to it. The problem is wheel spokes make it difficult to maneuver when you need to bend the rotor to that side.

If I needed to buy a tool for this, I would definitely go for Park Tool Rotor Truing Fork. It’s simple and thin enough to use it from any angle. Also, the gaps where the rotor is inserted are longer than your standard adjustable wrench and that makes it way more precise.

When truing the rotor all you need to make sure is that you start by little movements. Don’t bend it too hard unless you see that you are not getting the result at that spot. And remember, the bending is happening at the tip of the tool, so the angle of how you place the tool is the key to getting a good result. With a bit of practice, you will be able to straighten rotors with ease.

How To Clean Disc Brakes

Cleaning disc brakes can be a bit tricky at times. There are lots of stuff that you should be careful about, and some ways of cleaning won’t always work.

Cleaning Brake Calipers

The trickiest parts are the calipers on a hydraulic brake, especially inside the calipers where pistons are. To start you should always take the brake pads out when washing brakes, and never do the washing at the same time with washing your bike. Water will dissolve a bit of grease or oil if it finds it around the brake and soak the brake pads with it. There is usually some oil on a screw where the hydraulic hose enters the brake caliper.

When you’ve taken the pads out, you will need a quickly evaporating brake cleaner, preferably a bicycle-specific one. The reason it needs to be quickly evaporating is that on a hydraulic brake there can be none of it left on the brake pistons. The rubber seals inside get damaged by it quite easily even though most of them are branded as non-aggressive towards seals. I’m going so far as cleaning the inside of a caliper with a cotton earbud which is usually not necessary unless it somehow got greasy and oily in there. When it seems clean and all the brake cleaner is dissolved, you can place the brake pads back.

Cleaning Brake Pads

Brake pads are, unfortunately, almost impossible to clean. To tell you straight away, never even try soaking them in brake cleaner or degreaser. It literally does nothing but spread the already soaked oil more evenly through the brake pad.

Grinding the surface won’t work as well. The materials used on a brake pad work as a sponge and you need to somehow clean it from the inside. Since no chemical product can change the properties of oily substances used in brakes, you won’t find a solution with brake cleaners or similar products.

However, there is a tiny chance to get rid of it by extreme heat. Temperatures over 400 degrees tend to burn out those substances. But let’s be realistic, having a brake pad heated up to a point of almost melting is a waste of time and money. Replacing the brake pads is the only acceptable option if you ask me.

Cleaning The Rotors

If you are doing your brake maintenance regularly the chances are you can have perfectly clean rotors for years. Though the reality is that most of us don’t clean them until the brake stops braking properly or starts to squeal.

When that happens, it’s always best to take the rotor off the wheel and leave it to soak in a degreaser overnight. In this case, it’s always better to use degreaser over brake cleaner because degreasers are more powerful but more aggressive towards sensitive parts. In this case, aggressiveness is irrelevant so the more powerful degreaser is the better.

If you prefer to soak the rotors regularly, this may become a bit expensive method, however, there is always a solution. Isopropyl 99% alcohol will do the job effectively and it’s quite cheap for the volume you get. Be careful not to spill it on your skin or inhale it too much, it can cause irritation and get you dizzy.

If you, on the other hand, prefer to clean the rotor while on the wheel, make sure to use cotton earbuds or something similar to clean those holes in the rotor. The grease likes to stick there and even if the surface is clean, that grease comes off on the pads when braking. It’s better to use a brake cleaner in this scenario.

Sometimes grease and oil can get burned into a thin coating on the rotor and then it’s nearly impossible to clean without grinding it away with sandpaper. I’ve done it with all kinds of sandpaper and it doesn’t really make much difference, except that some require more or less time to do it.

 Cleaning Hydraulic Brake Levers

Brake levers are usually cleaned when cleaning the whole bike, however, if you’ve been bleeding the hydraulic brake there is a high probability that some of the fluid got spilled on a lever or even the shifter. Since brake fluids can make a lever slippery, or even cause damage to your skin and bike’s paint in certain amounts so it’s better to clean it right away.

Here the same principle as for brake calipers applies. You want to use something that evaporates quickly so it doesn’t get a chance to damage the seals or get inside the shifter where it can dissolve the grease and cause bad shifting. I tend to spray it carefully and wipe away immediately to avoid any unnecessary damage to my wallet.

Alternatives such as isopropyl alcohol which I mentioned earlier can be used but only if you know exactly where you can spray and where not, otherwise I would advise staying away with it.