How to check and change brake fluid

Checking and changing your car’s brake fluid

The following article should answer any questions you may have regarding your car’s brake fluid. You should be better equipped to know when you’re likely to need to replace it, what it’s expected to cost you, and how much of a job it could turn out to be if you decide to do it yourself.

How to check your brake fluid

To check your car’s brake fluid, the first thing you need to do is locate the brake fluid reservoir. Lift the bonnet and look for a plastic canister with a screw-on lid.

In older cars, the fluid is contained in the master brake cylinder. This is a metal box with a removable lid. The lid may have a metal clip that needs releasing to gain access to the fluid.

  1. Keep everything clean
    Even the smallest amount of dirt falling into the brake fluid can contaminate it. Dirt or dust in your brake fluid can damage the internal seals, causing poor performance and ultimately, brake failure.
  2. Open the brake fluid reservoir
    Unscrew the plastic cap (or remove the metal cover) to gain clear visual access to the fluid level. It’s important to work quickly; prolonged access to moist air can contaminate your brake fluid and render it useless. This also applies to leaving the cap or top off your new brake fluid container.
  3. Check the fluid level
    If the fluid isn’t within half an inch of the cap, add the correct type of brake fluid until it is. If the reservoir is empty, you may have to bleed your brakes when adding the new fluid.
  4. Check your brake fluid’s condition
    Brake fluid deteriorates in time. Ideally, it should be changed every 2 years. If it’s dark in colour, it’s a sign that it’s spoiled and ready for replacing. Your brake fluid should be translucent and a yellowish colour.

How to change your brake fluid

  1. If necessary, jack up your car to access your brake’s bleeder screws. You’ll find these on your wheel calliper or brake cylinder. They’re likely to be an 8mm or 10mm bolt.
  2. Remove the master cylinder cap and remove the existing brake fluid with a vacuum pump.
  3. Using a brake bleeder hose, attach one end to the furthest brake bleeder screw from the reservoir (the back wheel on the opposite side). Insert the other end into half an inch of fresh brake fluid that you’ve added to your drainage container.
  4. Loosen the bleeder screw and press the brake pedal until no air bubbles are visible, as you capture the fluid in your container. You’ll need an assistant to help you at this stage.
  5. Tighten the bleeder screw while your assistant keeps the brake pedal pressed firmly down as far as it will go.
  6. Repeat this action until no more bubbles appear.
  7. Add fresh brake fluid to the reservoir and ensure it remains full throughout the process. It’s imperative the reservoir never runs dry.
  8. Repeat for each brake calliper, working from the furthest away from the reservoir to the nearest.
  9. Top up the reservoir for the final time and replace the cap.
  10. Test your brake pedal and brake performance thoroughly before driving the vehicle in traffic.

How often should brake fluid be changed?

It’s recommended that brake fluid should be changed every 2 years, although you should be keeping an eye on it during regular maintenance checks. If it has been contaminated in any way, or if there’s a leak in the system, you must resolve the situation immediately.

How much is brake fluid?

Depending on the brand and quality, brake fluid costs around £2.50 to £5 per 500ml for containers of 500ml or 1ltr.

If you choose to buy larger quantities, a 5ltr container, for example, you can expect to pay between £20 and £30 in total.

Specialist high-performance brake fluids (most often used in motor racing) can cost you up to £15 to £20 per litre.

How much does a professional brake fluid change cost?

A brake fluid replacement should cost you somewhere around £50 or £60 at a garage. You could end up paying double that for the same work carried out by a car franchise or dealership, so it’s well worth shopping around.

How much brake fluid do I need to replace?

If your brake fluid is contaminated, then the answer is—all of it.

Any dirt or moisture will affect your braking performance and potentially damage the seals and components. Replacing your brake pipes, seals and hydraulics will be far more expensive than the costs of regular maintenance, so it pays to keep matters under control.

When do I need to check my brake fluid?

The moment you detect any problems with your brakes.

It goes without saying, braking is of paramount importance in vehicle safety, for you, your passengers and other road users.

If your brakes feel spongy, if they don’t work as well as usual, or if you hear any peculiar noises: grinding or squeaking, then have the whole system, including disks and pads, checked immediately.

Brake fluid types

Brake fluid is available in DOT 3, 4, 5 and 5.1. They each have different viscosities and boiling points, so it’s imperative to buy the correct type for your vehicle.

Brake fluids aren’t always interchangeable. For example, a DOT 5 is silicone-based where the other types are glycol-based.

The dos and don’ts of brake fluid

  • Brake fluid is toxic, so handle with great care. This also means you must discard of it properly at a toxic waste centre for disposal or recycling. It also includes any rags that have been contaminated with more than just a few drops.
  • Clean brake fluid off any paintwork immediately. It is highly corrosive, and it could eat through your paintwork or different finishes it in no time.
  • When checking the brake fluid for ABS systems, make sure to read the manufacturer’s guide before starting. In many cases, you’ll be expected to pump the brake pedal up to 30 times before inspecting your reservoir.
  • Avoid removing the reservoir cover/cap apart from when absolutely necessary. Every time you access the brake fluid to the air around you, you’re allowing an opportunity for contamination.