Brake Fluid Leaks in Cars: Causes, Diagnosis & More
What is Brake Fluid and What Does it Do?
Brake fluid is a hydraulic fluid used in hydraulic brake and hydraulic clutch applications in automobiles, motorcycles, light trucks, and some bicycles. It is used to transfer pressure from the brake pedal or clutch pedal to the wheel brakes or clutch mechanism to slow or stop the vehicle.
Brake fluid is typically composed of glycol ether and polyglycols to achieve certain desirable characteristics:
- It needs to be incompressible, so that pressure on the brake pedal is transmitted efficiently to the brakes.
- It must be stable at high temperatures generated by the brakes, typically -40°C to 180°C.
- It should absorb moisture from the air over time, so it needs to be hygroscopic.
By utilizing brake fluids with these specific properties, the braking system is able to operate safely, reliably and efficiently.
Common Causes of Brake Fluid Leaks
There are a few common causes of brake fluid leaks in cars:
Worn or Damaged Brake Lines
Over time, the metal brake lines in your car can corrode and develop small holes or cracks. This allows brake fluid to slowly seep out. Hitting large potholes or debris in the road can also cause damage to brake lines. Replacing old, worn brake lines is an important part of preventative maintenance.
Failed Brake Caliper Seals
The brake calipers have rubber seals to hold in the brake fluid. If these seals become old and cracked, they can leak fluid. Leaking caliper seals will usually cause one brake to lose pressure and fluid faster than the others.
Leaking Master Cylinder
The master cylinder is the main reservoir that holds brake fluid for the entire system. Internal seals in the master cylinder can fail over time, allowing fluid to leak out. This will cause a drop in brake fluid level and pressure throughout the system.
Loose Fittings
Loose brake line fittings, either at the master cylinder, ABS unit, or brake calipers can also allow small leaks. When fittings aren’t tight enough, vibration can allow fluid to seep out. It’s important to periodically inspect all brake fittings and tighten as needed.
Symptoms of a Brake Fluid Leak
A brake fluid leak can manifest itself through several symptoms that will alert you to a potential issue. Being aware of these signs can help you identify and address a leak before it leads to brake failure or more costly repairs. Here are some of the most common symptoms of a brake fluid leak:
Spongy brake pedal: Over time, a brake fluid leak causes low fluid levels in the brake master cylinder reservoir. This leads to air getting into the brake lines. When you press on the brake pedal, it will feel soft and spongy instead of firm due to the air compression. The braking force gets weaker, requiring you to push the pedal closer to the floor to stop the vehicle.
Brake warning light comes on: Modern cars have a brake fluid level sensor that illuminates the brake warning light on the instrument cluster if the level runs too low. So this warning light coming on can signify a leak and low brake fluid in the reservoir.
Pooling of fluid under car: Visually inspect under your car around the wheels and brake components. If you spot any puddles or dripping of fluid, it likely points to a leak in the brake system. The leaked brake fluid itself will be clear to amber in color.
Low fluid reservoir level: Pop your car’s hood and check the brake master cylinder reservoir level. The brake fluid level should be between the minimum and maximum markers on the reservoir. If it’s lower than the minimum marker, it indicates a brake fluid leak is occurring. Topping off the reservoir is just a temporary fix, as the leak itself needs to be addressed.
Dangers of Driving with a Brake Fluid Leak
A brake fluid leak is extremely hazardous and can have dire consequences if you continue to drive your vehicle without repairing it. Here are some of the main dangers:
Greatly Reduced Braking Ability
Brake fluid is responsible for transferring force to the brakes when you press the pedal. If you have a leak, this vital hydraulic pressure will be compromised. With less brake fluid, it becomes increasingly difficult for your brakes to work properly and slow the vehicle down.
You may find the brake pedal feels spongy or goes all the way to the floor when pressed. Your braking distances will be significantly longer too, taking much more time and distance to come to a stop. This makes it much harder to stop safely if needed.
Potential Complete Brake Failure
In severe cases of brake fluid loss, you may lose braking ability altogether. The spongy pedal may become completely unresponsive, unable to activate your brake pads or calipers at all. With no functioning brakes, you will be unable to slow down or stop your moving vehicle.
This brake failure is an obvious and serious danger, especially at highway speeds. Without brakes, a crash becomes nearly unavoidable if you need to suddenly slow down or stop.
Safety Hazard
All drivers depend on their brakes to control their vehicle and avoid accidents. With braking ability reduced or lost entirely from a leak, you and your passengers are at great risk whenever you drive.
Failing to repair a brake fluid leak jeopardizes everyone’s safety on the road. For your own good and that of others, it’s critical you do not drive until the leak is fixed and braking capacity is fully restored.
How to Diagnose a Brake Fluid Leak
Diagnosing a brake fluid leak relies on visual inspection as well as testing the braking system. Here are the main steps for diagnosing a brake fluid leak in your vehicle:
Visual Inspection
The first step is to visually inspect under your vehicle and around brake components for signs of leaking brake fluid. Brake fluid is typically a light amber or copper color. Look along brake lines and near fittings and joints for any wetness or stained areas. Also check around the brake master cylinder reservoir as this is a common source of leaks.
Check Fluid Reservoir Level
Pop your hood and locate the brake master cylinder reservoir. The fluid level should be between the minimum and maximum lines – if it is low, this indicates a brake fluid leak. Topping off the reservoir only to find it low again soon after confirms you have a leak.
Pressurize the System
With the engine off, depress the brake pedal several times to deplete any vacuum assist in the brake booster. Hold the pedal down and have an assistant inspect brake components and lines for any obvious fluid leaks. You may need to repeat this process a few times as it can be difficult to pinpoint a small leak. This pressurizes the system and will cause any leaks to become more apparent.
Finding evidence of leaking brake fluid requires immediate attention. Do not drive the vehicle and have it repaired to restore safe braking abilities. Identifying the source of the leak along with the proper repairs will get your brakes working safely again.
Repairing a Brake Fluid Leak
If you have determined a brake fluid leak exists in your vehicle, getting it repaired quickly is important for safe driving. Here are the typical steps involved in repairing brake fluid leaks:
Replace Worn Parts
The first step is to identify the source of the leak and replace any worn brake lines, hoses, caliper seals, or other components that are allowing fluid to escape. Your mechanic will thoroughly inspect the brake system to locate the leak and damaged components.
Tighten Fittings
Brake fittings can become loose over time, especially with brake fluid leaks that cause air to enter the lines. The mechanic will tighten any loose fittings throughout the system.
Flush and Replace Brake Fluid
After sealing the leak, the brake fluid will need to be completely flushed from the system and replaced with fresh, clean fluid. This ensures any accumulated water vapor, air bubbles, or contaminants are removed for optimal brake performance.
Cost to Repair a Brake Fluid Leak
The cost to repair a brake fluid leak can vary greatly depending on the cause and severity of the leak. Some of the major factors that affect the repair cost include:
Parts – If the brake fluid leak is coming from a damaged brake line or seal, the parts to replace those components can range from $20-$100 or more. More extensive leaks that require replacing calipers, wheel cylinders, master cylinders or ABS modulators will have much higher parts costs.
Labor Time – The time a mechanic needs to diagnose and repair the leak greatly impacts the total cost. A small external leak may only take 1-2 hours to fix, while a more internal leak could take 4 hours or more if brake components need to be removed. Shop labor rates average $100 per hour or more.
Fluid Replacement – A brake system flush and fluid replacement is recommended anytime the system has been opened up to repair a leak. The brake fluid itself is relatively inexpensive, but additional labor time is required to bleed the brakes. This can add $150 or more to the total.
With the cost of parts, labor and fluid replacement combined, the total bill to fix minor brake fluid leaks typically ranges from $250-$500. More extensive leaks requiring brake component replacement can cost $750 or more.
Preventing Brake Fluid Leaks
There are a few key things you can do to help prevent brake fluid leaks from occurring in your vehicle:
Routine brake inspections
Having your brake system inspected by a professional mechanic on a regular basis is important to help catch any potential issues early. Mechanics can check for leaks, worn brake pads, corroded brake lines, and any other problems that could eventually lead to a leak if left untreated.
Replacing worn parts early
Brake fluid leaks often start small before they become large leaks. Having worn brake pads, calipers, wheel cylinders, and brake lines replaced before they fail completely can help prevent bigger problems down the road. Don’t wait until parts are badly worn to have them serviced.
Proper driving habits to reduce wear
The way you drive has an impact on brake wear. Sudden stops, hard braking, and frequent short trips can all cause extra wear on brake system components. Practicing smooth braking and avoiding situations where you have to brake hard can help reduce unnecessary strain and extend the life of your brakes.
With vigilant brake inspections, early replacement of worn parts, and proper driving habits, you can help minimize the chances of annoying and potentially dangerous brake fluid leaks in your vehicle.
Signs You Need a Brake Fluid Flush
Over time, brake fluid can become contaminated with moisture, dirt, and other impurities that reduce its effectiveness. Here are some signs that it may be time to flush your brake fluid and replace it with fresh fluid:
Brake fluid appears dark/murky: Brake fluid is typically clear with a yellowish tint when fresh. If the brake fluid reservoir shows the fluid to be dark, murky or black, it’s a sign contaminants have built up and begun to break down the fluid. This will reduce braking performance.
Warning light comes on for no apparent reason: Modern cars have a brake fluid level warning light. If this light comes on, but you don’t have any brake fluid leaks or other issues, it may indicate moisture contamination in the fluid which is triggering the sensor. Flushing the old fluid can help clear the warning.
Routinely driving in severe conditions: Brake fluid can become contaminated faster if you routinely drive in wet, muddy, icy or snowy conditions. Road salt and other corrosives on the roads can also accelerate brake fluid breakdown. Flushing the fluid more regularly if driving in these types of conditions helps maintain optimal performance.
FAQ
Here are some of the most frequently asked questions about brake fluid leaks in cars:
Is it safe to drive with a brake fluid leak?
In most cases, no. A brake fluid leak indicates a problem with your brake system that needs to be addressed immediately. Driving with low brake fluid can lead to brake failure, which is an extremely dangerous situation. The only exception would be a very minor leak that hasn’t caused the brake fluid to go below the minimum mark – in that case, you may be able to carefully drive short distances to a repair shop. Otherwise, it’s best to get the vehicle towed.
How does a brake fluid leak affect the ABS system?
The ABS or anti-lock braking system relies on brake fluid to function properly. If brake fluid gets too low due to a leak, it can cause ABS malfunctions, warning lights, or complete ABS failure. This means you may lose anti-lock braking capabilities if the brake fluid is too low from a leak.
Can I just add more brake fluid if I have a leak?
No, simply adding more fluid is not a safe solution. The leak itself needs to be properly repaired in order to fix the issue. Just topping off the fluid without fixing the leak will likely lead to continued lowering of fluid levels as the leak continues. It’s best to have your brake system inspected by a professional mechanic.
What causes brake calipers to leak fluid?
Some common causes of caliper leaks include worn caliper piston seals, worn or damaged brake hoses, corrosion buildup on calipers, and issues with the brake fluid itself, like contamination. A thorough brake inspection can determine the exact cause in order to make the proper repairs.
Is it okay to mix different types of brake fluid?
No, you should never mix different types of brake fluid. Each type (DOT 3, DOT 4, DOT 5.1, etc) has different properties. Mixing them can decrease braking performance and lead to damage in the brake system components. Always flush the system thoroughly if switching fluid types.