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What Is Brake Fluid, And Why Do You Use It?
Brake fluid is a type of hydraulic fluid used in the braking system of automobiles and other machines with drum brakes where the shoe contact is not necessarily continuous. It usually consists of a mineral oil brake fluid like DOT 3, DOT 4, or Dot 5.1 and has additives to resist boiling and rusting from water vapor (or dew point) in air conditioning systems.
Since brake fluid is for occasional use only, it must be relatively clean and dry on the way to the master cylinder; otherwise, pedal travel will be increased as excess moisture absorbs some residual pressure. It must not make the pedal spongy.
The brake fluid used in a modern vehicle is designed to be non-compressible, and its performance is specified by European Standard WP.29e (also SAE J1703) for service braking at the wheels of passenger cars and light commercial vehicles up to 3.5 ton [1]. The American standard for heavy vehicles (SAE J1703) is slightly more severe; but the development of an equivalent European standard has been abandoned, due to disagreement on whether fluids should be allowed to compress, or only expand.
Some vehicles have vacuum-assisted brakes – these are sometimes called ”vacuum-assisted” or “pump and pray” brakes – which means the fluid can flow more slowly and easily, but at the same time, pump back up the master cylinder pipe (and hence foot pedal travel). This is only possible if the brake fluid is non-compressible; otherwise, there would be a pressure pulse in the system from which it would be difficult to recover. Also, many cars with vacuum-assisted brakes that are driven by a low-pressure power steering system cannot be serviced without removing the front wheels. Such vehicles are usually fitted with a separate reservoir for brake fluid.
How To Check Brake Fluid
Before starting the car, wipe off the dust and dirt on the front of your wheel as well as under it. Remove the wheel and brake caliper, then inspect the fluid level. Unfortunately, there is no easy or inexpensive way to do this without access to a sophisticated laboratory set-up with many specialized gadgets.
If the light looks clear and normal, then you have enough fluid. If it’s low or you see water droplets in it, check your car’s owner manual to find out if your car has a reservoir system – and if so how to refill it. You can sometimes check the level yourself, but most cars have the reservoir concealed behind a plastic plate, and even if you can see the fluid level, it may be impossible to tell exactly how much fluid is there.
If you do have access to a laboratory set-up with specialized equipment, you can use this to measure two things: The compressibility of the fluid under various temperatures and the water content. Compressibility is directly related to how hard the pedal feels – it’s harder to depress when there’s little or no compressibility in the brake fluid. If the fluid is very compressible, the pedal will feel soft and spongy, so you may want to look for a leak or for dried-up brake fluid.
How To Change Brake Fluid
Do not overfill the system with fluid, as this can lead to excess air in the system and a hard pedal. Brake fluid expands when it’s hot, so it’s important both to check that there is enough to fill the system (it is unlikely that the level will be exactly right) and to let it warm up before adding more.
When you remove a caliper, you need to hold it firmly – don’t just twist off a retaining clip by accident. Always allow at least 30 minutes for brake fluid replacement, as the brake fluid expands when it’s hot. This is vital if the car is driven immediately after a fluid change.
If the car goes into storage during winter, it’s vital to drain the system and fill it with good quality, non-silicone or water-soluble type of brake fluid. The volume of the reservoir will depend on the pressure generated by your braking system.
Remember that repairs to any vehicle can be dangerous and should always be carried out by an experienced professional. This guide is for informational purposes only and does not cover every possible scenario you may be faced with when performing this repair/maintenance procedure or wheel bearing.
How To Replace Brake Fluid
You should check your car’s owner manual to find out exactly how much fluid needs to be added or removed. You can do this by using a plastic funnel and sucking out some fluid (preferably with a friend at the wheel) or else trying to turn the wheel with the handbrake on and looking at whether there’s movement in the reservoir.
Each vehicle is different so you should refer to your owner’s manual or contact your local garage if you are unsure of anything. Consult your owner’s manual for a full list of the fluid types you’ll find in the reservoir. If a vehicle has a completely separate master cylinder, you’ll need to add brake fluid to the reservoir and then refill the system with brake fluid (but take care not to overfill it on this type of system as it’s difficult to detect a leak and can lead to an accident).
Most cars, particularly those with internal master cylinders, are now fitted with types of sensors that are able to check when braking is happening inside the car. This means that floor mats or any other material that can be caught under the wheels can be removed safely during this process.
How To Put Brake Fluid In Car
Remove the cap and allow as much fluid to drain down. Replace with new fluid and secure the cap. Check where the reservoir is in your car. The reservoir usually sits at the top of the master cylinder, but if you have to check it elsewhere, consult your owner’s manual or contact your local garage.
It is important to make sure that you do not overfill a car’s brake fluid reservoir; it is often concealed behind a plastic panel. Always refer to your car’s owner’s manual for guidance.
If you have an internal master cylinder, bleed some air from inside the system before refilling with brake fluid as this allows any air bubbles in the system to escape. When refilling, you need to test the fluid by pulling down on the brake pedal using a footstool or a bleeder screw on your diagnostic tool. If it feels very soft or spongy, check that the reservoir is not full. Also, make sure that no valves are sticking open and no washers are stuck to something so as not to get them caught in between the brake pedal and caliper.
Brake fluid does not expand in storage, so it’s important to let it warm up before adding more; give the reservoir time for this to happen.
Low Brake Fluid Symptoms
If brakes feel soft, spongy, and loose, check the reservoir.
Do not overfill the system as this can lead to excess air in the system, resulting in a hard pedal.
A hard pedal can be caused by overfilling your brake fluid reservoir. This is usually due to poor fluid quality or corrosion on its components. If you notice any of these symptoms after refilling with brake fluid, consult your car’s owner manual or contact a local garage to find out how much fluid you need to add.
Brake Fluid Tester
If you have an internal master cylinder, you will need to bleed the air from inside your system before using the brake pedal. Check your car’s owner manual for advice on how to do this. If there is a bleeder screw on your diagnostic tool, use it with a footstool; if not, put a bowl under the fluid reservoir to catch any fluid that leaks out when you depress the brake pedal.
If you’re checking or refilling your vehicle’s braking system, consult your owner’s manual or read through our informative guide linked above before doing so. Follow the steps, refer to the pictures and take care to ensure that everything is working correctly.
How To Bleed Brake Fluid In Car
Bleeding brake fluid is an important part of brake maintenance and can be done on every car if it’s done correctly. When you bleed your brake system, you remove air from the system so that it can work better. This reduces wear and damage to parts when brakes are applied and helps to prevent wheel lock-up, which can cause a serious accident. If you are unsure about doing the job yourself, contact a mechanic who can do the job for you on your behalf; this way you can sleep at night knowing that your brakes are working as they should be.
Always follow the manufacturer’s guide and manufacturer’s recommendations when doing any work on your brakes.
Do You Really Need To Change Brake Fluid?
Yes. You should change your car’s brake fluid at least once every 2 years, although it is recommended that you do it more regularly during the extreme weather of winter. If you have any problems with your braking system or the fluid, investigate them immediately and get them sorted as soon as possible.
Flushing The Brake System With Brake Fluid
If you can’t flush the brake system using a vacuum pump or by pulling down on the pedal, check for contamination of the master cylinder and/or caliper and replace it if necessary. You should now be able to add fresh brake fluid to replenish this. (Don’t forget to clean up any spillages when finished).
A brake fluid flush will remove fine particles of dust and dirt or other contaminants that can affect brake fluid performance and cause excessive stopping power.
Brake fluid also serves a vital function in your braking system. This is to lubricate your brakes, which allows them to work efficiently. Brake fluid also helps prevent corrosion of the brakes by forming a protective coating on all metal surfaces. This means that your brake system will last much longer than if it didn’t have this protective coating on the parts, which could lead to the need for repair or replacement at some point in the future.
