Is It Safe To Drive With a Bad Brake Master Cylinder

A brake master cylinder is where all the brake fluid is stored. Without the brake fluid, your vehicle brakes would not operate with full capacity. So, is it safe to drive with a bad brake master cylinder?

”It is not safe to drive with a bad brake master cylinder because if the master cylinder is bad, the brake fluid will leak out due to internal damage and your brake pedal could sink to the floor and you won’t be able to brake. It is not safe to drive your vehicle with no brakes.”


Is It Safe To Drive With a Bad Brake Master Cylinder

Is It Safe To Drive With a Bad Brake Master Cylinder

The brake master cylinder plays an important role. It has a function to converts the force of your foot into hydraulic pressure. By pressing the brake pedal, the master cylinder releases the brake fluid into the braking system and your brakes are activated.

When the mater cylinder is bad, it usually means that there is some internal damage with the seals and the braking fluid can escape from the braking system. Without the brake fluid, there can be no effective braking.

It is not safe to drive with a bad master cylinder because you basically do not have fully functional brakes. Your brake pedal could completely sink to the floor, or it could be spongy and braking will be very difficult.

If you notice any issues with the brakes, or if you notice any leakage from the master cylinder, make sure to take your vehicle to the repair shop and fix this issue as soon as possible.

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How Does Brake Master Cylinder Work?

The brake master cylinder is an important component of a vehicle. The brake master cylinder converts the force of the foot or fingers into hydraulic pressure. The master cylinder has a reservoir tank that contains the brake fluid and a cylinder. There are rubber piston cups which are located in the cylinder. The rubber piston cups form brake circuits.

How Does Brake Master Cylinder Work

Since there are two brake circuits such a master cylinder is called a tandem brake master cylinder. The ports of the master cylinder are located in the upper part of the cylinder. The outlet ports for the brake lines which are connected to the brakes are located on the side of the cylinder.

As soon as the driver presses the brake pedal, the push rod pushes the first rubber piston cup over the compensating port. Consequently, pressure builds up in the first brake circuit. As a result, the second rubber piston cup is moved over the second compensating port and pressure builds up in the second brake circuit.

Occasionally, brake lines can leak or snap. For this reason, split brake systems are mandatory in many countries. If one brake circuit fails, the second one still works.

Passenger vehicles typically have either a front-rear split brake system or a diagonal split brake system. In the front-rear split brake system, the first brake circuit provides pressure to the front brakes and the second brake circuit provides pressure to the rear brakes.

In the diagonal split brake system, one brake of the rear wheel and one brake of the front wheel are supplied by one of the two brake circuits. Portless master cylinders are used in conjunction with ABS. This type of master cylinder has no compensating port.

The brake fluid flows into the cylinder through a component called the breather port. The breather port provides the brake circuit with brake fluid when the intake valve is open. As soon as the valve is closed pressure, is being built up in the brake circuit and the vehicle is being braked.

What Are The Most Common Signs of a Bad Master Cylinder

A bad or failing master cylinder will send warning signs. It is important that you know which are those warning signs and to repair your master cylinder on time before you lose your brakes. Here are the most common signs of a bad master cylinder:

1. Brake pedal sinks to the floor

This is a clear sign of a failed master cylinder. Usually, when this happens, the internal components such as the seals have already failed and caused an internal leak. This will prevent the master cylinder from converting mechanical movement from stepping on the brake pedal to hydraulic pressure.

Hydraulic pressure is needed from the master cylinder to transfer the brake fluid to the brake caliper or wheel cylinder to help the vehicle stop. Without the master cylinder or hydraulic pressure, stopping would be both difficult and dangerous.

2. Difficult to stop while braking

If you have difficulties stopping while applying the brake pedal means that the master cylinder is close to complete failing. Before replacing the master cylinder, make sure that the brake master cylinder reservoir is full with braking fluid.

If the brake fluid is low, make sure there are no leaks at the brake lines, brake hose, brake caliper, and wheel cylinder. Just do a quick inspection and look behind the wheel for any signs of fluid leakage. If there are no leaks, fill the reservoir with brake fluid. While you are doing the inspection, you can also inspect the brake pads and see how thick they are.

3. Brake pedal feels mushy and spongy

If your brake pedal feels mushy and spongy, this could mean that there is air in the braking system. Usually, when there is air in the braking system it can mean that there is a leak somewhere, or the brake system has been worked on before.

For example, a brake caliper or wheel cylinder have been replaced but the mechanic forgot to bleed the air out. If there is no air left in the braking system after bleeding the air, your master cylinder has internal leaks and needs to be replaced.

Thank you for taking the time to read my article. Let me if this article helped you in diagnosing your vehicle problem. If you have any questions, please make sure to leave a comment and I would be more than happy to reply.

Igor Iwanowski

I am a certified Automotive Service Excellence (ASE) mechanic since 2018. I specialize in Brake systems, dashboard warning lights, EGRs, general engine problems, EVAP and Emissions issues.

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