The master cylinder in the BMW X5 is also known as the brake master cylinder. These contain the reservoir, which includes hydraulic fluid for working the braking system. They transfer the fluid to the brake circuit when you depress the clutch pedal.
BMW X5 master cylinder problems include the formation of air bubbles, grinding noise when applying brakes, brake warning light illumination, soft brake pedal, fluid leakage, and SUV drifting at one side.
I also faced braking components issue in my X5 while towing a bike carrier for an adventurous trip. The braking efficiency of my SUV was reduced, and it took more time to stop. I thought the issue came because of the towed vehicle. I removed the bike carrier and checked the braking efficiency while depressing the brake pedal, and the issue remained the same.
I realized the problem was not due to the towing vehicle; the faulty brake master cylinder caused this. It could not provide sufficient pressure for brake application. I replaced it to ensure safety while driving at high speed and during emergencies.
| Problems | Solutions |
| Air bubbles | Bleed the braking system |
| Grinding noise when applying brakes | Inspect brake components |
| Brake warning light illumination | Scanner tools for problem identification |
| Soft brake pedal | Use parking brakes as a substitute |
| Brake fluid leakage | Change broken seals |
| Contaminated brake fluid | Replace contaminated fluid |
| SUV drifting at one side | Press the clutch pedal to check the drifting side |
Formation of air bubbles
The formation of air bubbles in the brake master cylinder is a significant problem that reduces the efficiency of the braking components.
Air does not allow the system to build enough pressure for efficient braking. Air can enter the system because of broken and damaged seals and airlines.
Air enters the system when its seals break. Degradation of rubber material causes damage to the seals, and they allow the air to get inside.
In addition, air can also enter the system because of incorrect installation of seals. You can face problems because of leaky hydraulic lines because of exposure to high temperatures, failure of hoses, and age.
My friend called me, and he told me that the brake pedal of his vehicle felt spongy and sinking toward the floor. Moreover, he also complained about the increased stopping distance.
I recommended depressing the brake pedal and checking air bubbles near the brake master cylinder reservoir. He did the same and told me he saw air bubbles near the reservoir.
I replied that the issue in your SUV came from air bubbles in the braking system, and you have to bleed it for air removal. He bled the brake system by draining the old fluid and flushing the new fluid.
Moreover, I advised to ensure that all seals and hoses are fine and properly connected. Replacement of broken seals with new ones is necessary to reduce air bubble formation.
Grinding noise when applying brakes
Many people complain that they hear the grinding noise during brake application. You cannot drive with this grinding noise because it can damage the braking system components.
The grinding noise indicates the malfunctioning of the brake master cylinder. These are vulnerable to damage because of their age and continuous pressure application.
Grinding noise issues can also arise from insufficient hydraulic pressure on the front and rear brakes. It can also affect the driving conditions and efficient braking when it cannot convert the foot’s brake pedal pressure to hydraulic pressure.
You have to inspect the braking components to identify the origin of the grinding noise. Sometimes, it can also come because of broken rotors and pads.
Replace the broken brake rotors and pads with new ones. Moreover, you have to replace the worn-out rubber seals with new ones to maintain the efficient brake master cylinder functioning.
Brake warning light illumination
Sometimes, brake warning lights illuminate on the display screen because of faulty braking system components, including the master cylinder.
The warning light shows a low brake fluid level, affecting braking efficiency. Low brake fluid levels also decrease the hydraulic pressure and cause problems.
Fluid levels decrease because of the damaged reservoir and due to their broken rubber seals that are not designed to last longer.
Damaged hydraulic lines also cause leakage, and the brake master cylinder cannot provide enough hydraulic pressure to the front and rear brakes.
You can use the scanner tools to identify the reason for the brake warning light on the screen. My friend also faced the issue, and he could not recognize the problem.
He went to the BMW dealerships, and they used the OBD II scanner tools to find the faults in the system.
Soft brake pedal
BMW X5 brake pedal becomes spongy and soft when you depress the brake pedal. In addition, it functions unevenly and quickly moves back to the floor.
These become soft and spongy because of insufficient brake fluid and hydraulic pressure. Pressure decreases because of damaged seals of the master cylinder and hydraulic fluid lines.
Brake fluid level also decreases because of their age and continuous use. I also faced the same issue while driving on the highway. I pressed the pedal, but the brakes did not apply efficiently. I was vulnerable to collision with the forward vehicle because of the increased braking distance.
I became scared and used the electronic parking brakes to cope with emergencies. It shows that parking brakes in your vehicle are used as a substitute.
Brake fluid leakage
Worn-out or bad master cylinder components increase the risk of hydraulic fluid leakage. The fluid does not remain in the cylinder because of the broken parts.
Hydraulic fluid is susceptible to leakages because of broken hydraulic fluid lines. The master cylinder reservoir is also at risk of cracking because of its material, high temperatures, and exposure to certain conditions.
Cracks in these parts allow the fluid to come outside and decrease the overall pressure that is required to stop the wheels.
These cylinders contain rubber seals to keep the fluid inside. Rubber seals can get damaged because of their age, delicate material, and high temperature.
Inspect its components and replace the rubber seals if they are broken. Use seals of the correct size for their proper installation and functioning.
Contaminated brake fluid
A bad master cylinder in the BMW X5 increases the chances of fluid contamination, enhancing the chances of overheating braking components.
Seals of these components reduce the chances of leaking by keeping the hydraulic fluid inside and protecting the fluid from dust, rust, and contaminants.
These seals do not allow external contaminants to enter and contaminate the fluid. These contaminants can enter the master cylinder and contaminate the fluid because of broken seals.
Contaminated fluid can also damage the braking components when traveling between the lines.
Fresh fluid appears amber in tone, while contaminated fluid is dark brown or brownish-black. Replace the brake fluid when it appears brownish-black.
BMW X5 drifting at one side
The brake master cylinder contains two brake circuits to stop the rear and front wheels. Sometimes, one of the circuits fails to perform its function and applies enough pressure to the rear or front wheel.
People usually complain that their BMW X5 rear and front brakes are not functioning, which causes a drifting issue. You can face pulling at one side because of the working of one brake circuit and the application of the brake on one side.
Drifting at one side increases the chance of rolling over and serious accidents. You should inspect the brake circuits and hire a mechanic to fix them. Press the pedal to check which side of your X5 is drifting.
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