Brake fluid is a hydraulic fluid that is critical for the safe and effective operation of your vehicle’s brake system. It transfers pressure from the brake pedal to the brake calipers to slow or stop your vehicle. However, over time brake fluid can become contaminated, compromising braking performance and safety.
What Causes Brake Fluid Contamination?
There are several ways brake fluid can become contaminated:
One of the most common causes of brake fluid contamination is moisture absorption. Brake fluid is hygroscopic, meaning it readily absorbs moisture from the air. This moisture can enter the brake system through:
- The master cylinder’s vented lid or seals
- During brake fluid top-ups if the reservoir is left open
- Permeation through rubber hoses over time
Even small amounts of water contamination can begin chemically breaking down the brake fluid, reducing its boiling point and lubrication properties.
Unwanted particles like dirt, debris or residue can also contaminate brake fluid if care is not taken during servicing. Potential sources include:
- Using low quality or improper brake fluid
- Residue or contaminants in the container used for topping up
- Not cleaning the master cylinder cap and reservoir before adding fluid
- Allowing debris into open lines during brake work
These particulate contaminants can compromise the integrity of the hydraulic system.
Mixing different types of brake fluid, or introducing other automotive fluids like power steering or transmission fluid can also lead to contamination. Different brake fluids have different chemical compositions, and mixing them leads to a compromised blend.
Tiny metal particles from brake pad wear and rotor debris can also make their way into the fluid over time. As internal brake components slide and wear against each other, metallic particulates can accumulate in the hydraulic system.
External brake fluid leaks, such as from worn or damaged hoses, seals, and valves, can allow contaminants to enter the system from the outside environment. Anything from road debris to water can contaminate the fluid if given a chance to leak in.
How Does Contaminated Brake Fluid Affect Performance?
Contaminated brake fluid can seriously compromise braking system performance and safety:
- Decreased Braking Power – Contaminants reduce the hydraulic pressure capacity of the fluid, leading to soft, spongy pedal feel and reduced braking force.
- Brake Failure – In extreme cases, contaminated fluid can cause complete brake failure by blocking valves or seizure of components. This poses a major safety risk.
- Corrosion – Moisture causes the fluid to be more corrosive, leading to corrosion of internal brake components like master cylinders and caliper pistons. This reduces their lifespan and function.
- Boiling – The boiling point of brake fluid drops as it becomes contaminated. This increases the chance of fluid vaporization and brake fade under hard braking.
- Rubber Degradation – Additives that maintain the integrity of rubber seals and hoses break down as the fluid becomes contaminated. This leads to leaks and further contamination.
- Noise – Contaminants like metal particles and moisture create noise in the hydraulic system, evident as squeaking or grinding.
- Less Lubrication – Contaminated fluid provides less lubrication to internal components like brake caliper pins, causing them to seize up or drag.
How To Prevent Brake Fluid Contamination
Here are some key steps to help prevent brake fluid contamination:
- Use Quality Fluid – Choose a high quality, brand name DOT 3 or DOT 4 brake fluid that meets SAE standards. Avoid cheap, low quality fluids.
- Change Fluid Regularly – Flush and replace your brake fluid according to the vehicle manufacturer recommendation, usually every 2-3 years.
- Avoid Mixing Types – Never mix DOT 3 and DOT 4 brake fluid, as they have different chemical compositions.
- Clean Components – Ensure the master cylinder cap and reservoir are clean before adding fluid. Carefully wipe the rim and threaded cap area to prevent debris entering the system.
- Seal Containers – Keep unused brake fluid in a sealed container to limit moisture absorption until you are ready to use it. Discard old fluid.
- Fix Leaks Promptly – Inspect brake components regularly and fix any leaks immediately to prevent external contaminants entering the system.
- Bleed Thoroughly – Anytime the system is opened up, bleed the brakes thoroughly afterward to flush out air, moisture and contaminants.
FAQs About Contaminated Brake Fluid
How do I know if my brake fluid is contaminated?
Warning signs of contaminated brake fluid include a spongy brake pedal, need to pump the brakes, grinding or squeaking noises during braking, brake fluid that is dark or murky, and reduced stopping power.
Does contaminated brake fluid damage brake system components?
Yes, contaminated fluid can corrode and damage master cylinders, brake lines, valves, calipers, wheel cylinders and rubber seals over time. Significant contamination can lead to outright component failure.
Should I just top off low brake fluid rather than flushing it?
No, you should never just top off the reservoir without a complete flush. This will simply dilute the contaminants without actually removing them from the system.
Can I mix different types of brake fluid?
No, DOT 3 and DOT 4 brake fluid should never be mixed, as they have different chemical compositions. Mixing can cause the blend to be unstable.
How often should I flush and replace my brake fluid?
Experts recommend a complete brake fluid flush and replacement every 2-3 years. Check your vehicle owner’s manual for specific intervals recommended by the manufacturer.
What is the consequence of driving with badly contaminated brake fluid?
Driving with significantly contaminated brake fluid can be very unsafe, as it can greatly reduce braking performance and lead to system failures. Never drive if you suspect your brake fluid is badly compromised.
- Brake fluid easily becomes contaminated through moisture absorption, particulates, improper mixing, and external leaks.
- Contaminated fluid causes decreased braking power, corrosion, noise, and component failures.
- Prevent contamination by using quality fluid, changing it regularly, avoiding mixing types, sealing containers, and fixing leaks immediately.
- Signs of contaminated fluid include spongy pedal feel, grinding noises, dark/murky color, and reduced stopping ability.
- Never just “top off” low brake fluid without a flush, as this dilutes but does not remove contaminants.
Keeping your brake fluid clean, moisture-free, and well maintained is crucial for safe braking performance. Take steps to prevent contamination, and replace your brake fluid regularly as part of routine maintenance. Your safety on the road depends on clean, uncontaminated brake hydraulic fluid.