How does a master brake cylinder work?
The role of the master cylinder is to convert the force applied to the brake pedal into hydraulic pressure. The master cylinder does this by supplying brake fluid to the brake circuits.
It also regulates the amount of brake fluid transferred depending on the pressure applied to the brake pedal. Whether your car has drum or disc brakes, it has a master cylinder.
The law requires vehicles to have two separate brake circuits. The hydraulic pressure generated for them comes from a tandem master cylinder. Therefore, if one brake circuit fails, the other already has all the brake pressure to remain functional.
Every time you press the brake pedal with your foot, the pressure piston receives the force of your foot. This makes the piston move closer to the brake line.
In older cars, the braking force is generated by the piston collar passing through the bore after the pressure chamber closes. Modern cars have a spring that holds the pressure piston back, so that it returns to its original position when you take your foot off the brake pedal.
When this happens, the brake fluid flows back into the master cylinder, thus increasing the brake pressure again the next time you press the brake pedal.
Where is the master cylinder? Typically, the master cylinder is located just above the driver’s side firewall (which separates the engine compartment from the interior of the vehicle), very close to the brake fluid reservoir.
All you have to do is find the brake fluid reservoir and follow the brake lines that lead to the master cylinder and the brake booster.
Brake Master Cylinder vs Brake Booster
Both the master cylinder and the brake booster are important components of your car’s braking system and work together to stop your car, but that’s where the similarities end.
The master cylinder is responsible for distributing brake fluid to the brakes, while the brake booster makes it easier to apply the brakes by increasing the force you apply to the brake pedal.
This means that if the first one fails, your vehicle will not be able to stop. On the other hand, if the brake booster fails, it will only make braking harder and your stopping distance longer.
If one of these components fails completely, it could lead to a serious accident. But with the master cylinder, the situation would probably be even more serious.
What causes a master cylinder to fail? Wear and tear
Brake master cylinders, like any other part of your car, will wear out over time. Internal seals and components will fail and wear out over time.
Dirty Brake Fluid
Brake fluid is important to your vehicle’s braking system, just like motor oil is to your engine. Brake fluid doesn’t get dirty as quickly as engine oil, but it still needs to be changed regularly.
Leaving brake fluid to deteriorate for long periods of time can cause damage to the master cylinder, as contaminants such as water, mud, and other debris can break down the rubber seals and cause corrosion.
Manufacturing Defects
Although rare, it is possible for a master cylinder to have a manufacturing defect, especially if it has already been replaced with a replacement (non-OEM) part. If a defective component was used during manufacturing, the master cylinder may fail sooner than expected.
How much brake fluid does the master cylinder reservoir hold? On most vehicles, the master cylinder reservoir holds 230-350ml of brake fluid. However, this amount may vary depending on the make and model of your car. You will need to consult your vehicle’s owner’s manual or service manual to find out the exact capacity of your master cylinder reservoir.
When checking your brake fluid level, pay attention to the condition of the fluid and the markings on the container. The container should have “MAX” and “MIN” lines indicating the recommended limits. Underfilling and overfilling can both cause complications in the brake system.
Inspecting the Master Cylinder
If you suspect that your vehicle’s master cylinder is defective, you should have it inspected immediately. Luckily, you can do this yourself by following these steps:
1. First, make sure your car is parked on a level surface and engage the parking brake.
2. Open the hood and locate the master cylinder. As mentioned earlier, it usually mounts on the firewall near the driver’s side and connects to the brake booster.
3. Inspect the components for visible damage like cracks, leaks, rust, etc.
4. Check the brake fluid level in the reservoir as a low brake fluid level may indicate a problem with the master cylinder.
5. Test the operation of the brake pedal. A defective master cylinder can cause the pedal to feel squishy, ​​spongy, or to slowly sink to the floor when you press it.
6. Check the dashboard to see if any warning lights are illuminated. If your brake warning light comes on, it could be an indication of a faulty master cylinder.
If you don’t feel confident checking the master cylinder yourself, or you simply don’t have the time, consult a professional mechanic (or a neighbor who regularly works on their car) for help.
