Brake Fluid

How to Check and Change Brake Fluid

Brakes are one of the most important components on a car, and if they’re not up to standard you could find yourself in serious trouble incredibly quickly, either in the form of a failed MOT or worse. Thankfully there are ways you can keep on top of your braking system and keep you in the safest condition when on the road, including making sure your brake fluid is in a good condition and changing if necessary. 

Brake fluid reservoir of brake system in the car

What Does Brake Fluid Do

Brake fluid is a hydraulic fluid used in hydraulic brake and clutch application and is used to transfer the force you press onto the pedal into pressure to the front and rear brakes, thereby stopping the car. The fluid converts the energy through the brake line, compressing the brake pads and squeezing on the rotors. If you have a drum brake system this will also rely on brake fluid as an important component.

Why Do I Need to Check My Brake Fluid 

Keeping on top of your brake fluid is an important part of maintaining your vehicle, and any issues with your braking system is a fast-track to an otherwise avoidable accident. Over time your brake fluid will become contaminated with both water and metal particles from the braking system, and these contaminations make the liquid more compressible, which reduces the effectiveness of the brake pedal. Making sure you check and change the fluid will prevent corrosion and vastly reduce the risk of any components failing.

What Happens If My Brake Fluid Gets Low?

A lack of brake fluid in your vehicle can be incredibly dangerous, as it has a big impact on the performance of your brakes. The space where your brake fluid should be gets filled instead with air, and when this happens, your brakes will begin to feel spongy and unresponsive. This can cause your braking time to suffer and require you to use excessive force just to apply the brakes all the way.

How to Check Brake Fluid

Brake fluid can be checked relatively easily – and you want to make sure you do it regularly and not rely solely on your dashboard warning lights. Every few months you should drive your vehicle for a short period, making sure you press the brake several times to ensure the system has been properly filled. Once you’ve pulled up, park on a flat surface, open the bonnet and find your brake fluid reservoir (if you can’t find it check your owner’s manual). You should be able to see how much fluid is in there through the sides of the reservoir, and if it’s below the low marker, you’ll need to top it up.

Can I Replace Brake Fluid Myself?

Yes, but it can be a pretty tricky task and is nowhere near as simple as asking yourself “can I just pour new brake fluid in”. If you understand the following points, you might be able to have a crack at it:

  • Drain the existing brake fluid entirely.
  • Clean the reservoir with a soft, lint-free cloth – if you can access it.
  • Pour in your new brake fluid until it reaches the ‘FILL’ line.
  • Bleed your brakes until the bleeder screw fluid is running clear.

We’ve explained this process in more detail further down the page.

What Brake Fluid do I Need for My Car

There are a number of different types of brake fluid, but they can be grouped into two main categories – glycol based and silicone based. Within these types there are a number of ‘DOT’s, which stands for Department of Transport. In essence, the higher the number, the higher performance you can expect. Most vehicles on the road today will require DOT4, but it is worth checking in your owner’s manual, or on your master cylinder fluid reservoir cap, as this will let you know what to purchase.

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How Often to Change Brake Fluid

As your brake fluid absorbs water and potentially becomes contaminated with metal particles, your brakes become less and less effective. In order to keep your brakes working at their best condition, most manufacturers recommend that your brake fluid is changed every two years.

How to Change Or Top Up Brake Fluid

Changing brake fluid is a much more in depth task than changing oil, and will require a few pieces of equipment to help you along the way – not least a friend to help you. To begin with, you’ll need to drain off all the old fluid. To do this, take off the master cylinder cap and use a syringe, or similar, to remove as much of the fluid as possible, decanting into a suitable container. Once you’ve got as much as possible out of the reservoir, you’ll need to jack the car up onto axle stands, remove the wheels and start working on the brakes. 

Before you put any new fluids in, you’ll need to clean out any debris from the reservoir, using a lint-free cloth. Once cleaned, fill the master cylinder back up to the MAX line, but make sure you only use fluid from a brand new, sealed, container as any open containers will absorb moisture from the air. 

Each brake calliper has a bleed nipple on the back, and this will need to be released in order to let the old fluid out. Before doing so it’s best to spray some brake cleaner and penetrating oil on to free it up, and it’s likely to be full of road dirt. Connect a small rubber hose to the nipple and submerge the end of the hose into the container holding the old brake fluid.

Now put a small block under the brake pedal to avoid it from pressing too far down to the floor, and ask your friend to sit in the driver’s seat. Beginning with the calliper or wheel cylinder denoted in your owner’s manual, open the bleed nipple and shout “down”, getting your friend to repeat it back to you once they have pressed the pedal. Now close the nipple, shout “up” and have your friend repeat it back once they’re off the pedal. If this is done while the nipple is open you’ll just suck air into the system, which is the opposite of what you’re trying to achieve. Each pump you’ll see fluid coming out of the nipple, along with air bubbles, which you are trying to remove. Keep going with this system until the new fluid is coming through and there are no air bubbles. You will need to keep an eye on the master cylinder fluid levels, as if you pump the pedal when the level is too low, you’ll just pump air into the system, ruining all of your previous hard work.

Keep doing this across all four wheels and you should notice the pedal feeling firm, meaning you have a brake system full of good quality fluids. Check the master cylinder levels again and top up if necessary, close the cap, put the wheels back on and you’re good to go. Brake fluid is not toxic on its own, but can quickly become dangerous if contaminated, so must be disposed of correctly. The easiest way to do this is take it to your nearest recycling centre that caters for hazardous materials.

How Much to Does it Cost to Change Brake Fluid

Despite being a potentially lengthy process, changing brake fluid is not all that costly if you take it to your nearest garage. On average you’ll pay approximately £50 for a brake fluid change, although at some of the more well-known national garages you can expect to pay between £35–£40

How Much Brake Fluid Do I Need

Your brake fluid reservoir will hold approximately half a litre, but because of the amount you’re likely to need to use when flushing the system through, it’s usually best to play it safe and have two litres to hand. Most bottles come in either 500ml or a litre and are usually much better value if buying the larger size.

Is It Possible To Use The Wrong Brake Fluid?

Yes, you can use the wrong brake fluid in your vehicle. We covered the most commonly suitable types further up the page, with DOT4 being especially popular. Failing to check your vehicle’s specs and accidentally using the wrong type of brake fluid could cause serious damage to your car.

For more hints and tips on how to get the best out of your car for longer, visit our Car Care hub, answering any and all questions you may have about motoring. Or, if your brakes are broken and your car on the whole is beyond repair, get a quote from Scrap Car Comparison today and find out how much you could sell it for, whatever condition it’s in! Our UK-wide service includes free collection and finds the best offers from your local scrap and salvage buyers! Call our team on 03333 44 99 50 or use our scrap car price calculator for a valuation in just 30 seconds.

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