How To Maintain Hydraulic Disk Brakes

A huge number of bikes, from mountain bikes to through to hybrid and road, now come as standard with hydraulic disk brakes. We are talking entry level bikes upward here – not just high-end superbikes any more. Hydraulic disc brakes are one of those bike components that can seem a little intimidating until you get to know them. The good news is that most routine maintenance is straightforward, and you don’t need to start messing around with hydraulic fluid or bleeding every time your brakes need some attention.

For everyday home maintenance, the main jobs are keeping the braking surfaces clean, replacing worn brake pads, and making sure the caliper is correctly aligned so the rotor spins without rubbing.

Here’s how to do it.

Getting to know your disc brake

The photo above shows the main parts you’ll be dealing with:

- Rotor – the metal disc attached to the wheel.

- Caliper – the part mounted to the frame or fork that contains the brake pistons.

- Brake pads – these sit inside the caliper and squeeze the rotor when you pull the brake lever.

- Pad retaining bolt or split pin – stops the pads from escaping from the caliper. Depending on your brakes, this may be a threaded bolt, a split pin, or a similar retaining system.

Before starting, it’s worth checking the instructions for your particular brake model. The basic process is similar across most hydraulic brakes, but pad retention, recommended cleaners and torque settings can vary.

When do your brake pads need changing?

Brake pads gradually get thinner as you use them. How quickly this happens depends on where and how you ride: wet and gritty conditions can eat through pads surprisingly quickly.

If the brakes are becoming noisy, feel weaker than usual or you can see that there’s very little braking material left, take a closer look.

Remove the wheel and inspect the pads. You’re looking at the friction material, not the metal backing plate it is attached to. If the friction material is close to the manufacturer's minimum thickness, replace the pads.

Don't try to squeeze every last ride out of them. Completely worn pads can damage the rotor and leave you with very little braking power.

Removing the old brake pads

With the wheel removed, don't pull the brake lever. Without the rotor between the pads, the hydraulic pistons can move too far out of the caliper.

Now find the pad retaining bolt or split pin, as shown in the photo.

If yours uses a retaining bolt, remove it using the appropriate tool. Some bolts also have a small safety clip that needs to come off first.

If it uses a split pin, straighten the bent end and carefully pull the pin out. Manufacturers may specify replacing a split pin rather than reusing it, so check the instructions for your brake.

You should now be able to slide the pads and their spring out of the caliper. Take note of how the spring and pads fit together before pulling everything apart – a quick photo with your phone can save some head-scratching later.

Give everything a clean

Disc brakes work best when they're clean. Unfortunately, they're also particularly sensitive to contamination.

Oil, chain lubricant, grease and some cleaning products can all contaminate the pads or rotor. Even touching the braking surface with greasy fingers isn't a great idea.

Use a clean, lint-free cloth and a disc-brake-safe cleaner or the cleaning method recommended by the brake manufacturer to clean the rotor.

Avoid spraying cleaners or lubricants indiscriminately around the bike. Never put lubricant on the rotor or brake pads.

If the pads have been contaminated with oil, replacement is generally the safest option. Cleaning the rotor but reinstalling badly contaminated pads can simply transfer contamination straight back onto it.

Resetting the pistons

As brake pads wear, the caliper pistons gradually move further outward to compensate. New pads are thicker, so you'll normally need to push the pistons back into the caliper before fitting them.

Ideally, do this with the old pads still fitted or with a suitable piston-pressing tool. Apply slow, even pressure rather than forcing one piston aggressively.

Take particular care with ceramic pistons, which can be damaged by inappropriate tools or uneven force.

Again, don't squeeze the brake lever while the pads and wheel are removed.

If a piston won't retract normally, repeatedly sticks, or you notice hydraulic fluid around the caliper, stop there. The brake may need servicing rather than simply a new set of pads.

Fitting the new pads

Fit the pad spring between the new pads in the same orientation as the old ones, then slide the assembly into the caliper.

Reinstall the pad retaining bolt or split pin.

For a retaining bolt, tighten it to the brake manufacturer's specified torque and refit any safety clip. For a split pin, install it according to the manufacturer's instructions and secure it as specified.

This small component is important: it's what keeps the pads where they're supposed to be.

Before putting the wheel back in, check that both pads are seated correctly.

How to stop disc brakes rubbing

A faint intermittent sound can sometimes come from a slightly imperfect rotor, but constant shhh-shhh-shhh rubbing usually means something needs adjusting.

First, make sure the wheel is seated correctly and the axle or quick release is properly secured. There's little point adjusting the caliper around a wheel that's sitting crooked.

Spin the wheel and look through the caliper. Ideally, you'll see a small gap between the rotor and each brake pad.

If the rotor constantly rubs one pad, the caliper may simply need centring.

The quick caliper-alignment method

Slightly loosen the two bolts that attach the caliper to the frame or fork. Don't remove them – you just want the caliper to be able to move sideways.

Now:

- Squeeze and hold the brake lever firmly.

- While holding the lever, tighten the caliper mounting bolts gradually and evenly.

- Release the lever.

- Spin the wheel and listen for rubbing.

This often centres the caliper nicely.

If it still rubs, loosen the mounting bolts slightly and align the caliper by eye, making tiny adjustments until you can see clearance on both sides of the rotor. Then tighten the bolts to the manufacturer's specified torque.

What if it only rubs at one point?

Watch the rotor as the wheel spins.

If the gap is good for most of a revolution but the rotor moves sideways and touches a pad at one particular point, the rotor may be slightly bent rather than the caliper being misaligned.

Minor rotor straightening is possible with the correct tool and a careful hand, but don't keep bending a badly damaged rotor back and forth. A significantly bent, cracked, deeply scored or otherwise damaged rotor should be replaced.

Also check the rotor thickness against the manufacturer's minimum specification when it's showing significant wear.

Don't forget to bed in new pads

Fresh pads and a clean rotor won't necessarily provide maximum braking power immediately. New pads need to bed in against the rotor.

The exact procedure varies between manufacturers, but it generally involves a series of controlled stops to gradually bring the brakes up to temperature and transfer an even layer of pad material onto the rotor.

Follow the bedding-in procedure supplied by your brake or pad manufacturer.

Don't skip this part. Properly bedded-in brakes generally feel stronger, more consistent and quieter.

A quick post-maintenance check

Before heading off for a proper ride, squeeze the brake lever several times. It should feel firm and the pads should engage the rotor normally.

Spin the wheel and check that it turns freely without significant brake rub. Check that the wheel is secure, the caliper mounting bolts are correctly tightened, and (importantly) that the pad retaining bolt, safety clip or split pin is correctly installed and secured.

Then test the brakes at low speed somewhere safe before relying on them on the road or trail.

If the lever pulls unusually close to the handlebar, feels spongy, braking power is poor, there's a hydraulic-fluid leak, or you're unsure whether something has been assembled correctly, don't ride the bike until the brake has been properly checked.

Clean brakes are happy brakes

You don't need to dismantle your hydraulic system every few weeks to keep disc brakes working well. For most riders, a little routine attention goes a long way.

Keep the rotor clean, check your pad thickness periodically, replace worn pads before they're completely gone, and deal with rubbing rather than simply putting up with it.

Once you've changed a set of pads and centred a caliper a couple of times, hydraulic disc brakes become much less mysterious – and keeping them quiet and powerful is a very satisfying home-mechanic job.

If this all seems a bit much or you can't quite get your disc to stop rubbing, then drop into Bike Hero’s Chertsey workshop anytime and one of our friendly mechanics would be happy to walk you through any of these steps to help you get strong and noise-free disc brakes.