What Are The Signs Of A Bad Master Cylinder?
A bad brake master cylinder can manifest itself in several ways.
Here are the most common signs:
1. Misbehaving Brake Pedal
The brake pedal is often a mirror for problems in the brake system.
With a bad brake master cylinder, your brake pedal will likely feel soft and mushy. There may be excessive brake pedal travel, and it might even sink entirely to the floor. It’ll be slow to bounce back to its original position, or worse, not return at all.
The common culprit is often a damaged rubber seal inside the master cylinder.
More importantly, if the master cylinder doesn’t function correctly, the brakes won’t receive enough pressure to efficiently stop the wheels.
Meaning, your brake calipers won’t get sufficient pressure to clamp the brake pads onto the brake rotors. And wheel cylinders will have trouble delivering brake shoe pressure onto a brake drum.
2. Brake Fluid Leak
A brake fluid leak can happen at almost any point in the braking system — from the master cylinder, brake line, to the caliper piston in disc brakes (or wheel cylinders in drum brakes).
Fluid leakage from the master cylinder can be due to a few things, like:
- Damaged master cylinder rubber seals
- Unsecure master cylinder reservoir
- Cracked old master cylinder housing or brake fluid reservoir
So, it’s always a good idea to regularly check the brake fluid reservoir level and keep an eye out for any brake fluid leaks under your car.
3. The Brake Warning Light Is On
If your vehicle has brake fluid or pressure sensors, they’ll set off an alert when the brake fluid level or hydraulic pressure is too low. This is when the brake warning light or check engine light illuminates.
If the brake warning light pops on, it’s a clear sign that something is wrong with the brake system.
But the check engine light can imply many things, not just braking system problems. In this case, you’ll likely need an OBD code diagnosis to isolate the actual issue.
4. Contaminated Brake Fluid
The master cylinder seals not only ensure that the brake fluid stays in — they also keep external contaminants like dirt, dust, and rust out.
Damaged or broken seals won’t only leak fluid. They’ll also let all these contaminants and air in, adversely affecting braking performance.
New brake fluid is typically a clear, amber tone (if you’re using the usual DOT 3 brake fluid or DOT 4). Contaminated brake fluid can range from dark brown to almost black.
And while brake fluid will naturally degrade over time, fluid that’s degrading faster than usual, combined with other bad brake symptoms, can indicate brake hardware issues.
5. Vehicle Drifts When Braking
The brake master cylinder typically has two separate hydraulic brake circuits, where 1 brake circuit controls 2 wheels. This is a safety measure to ensure that the other circuit can still stop the vehicle if one hydraulic circuit fails.
A failure in one brake circuit may cause the vehicle to drift to one side when the brakes are applied, as only one circuit is functioning effectively.
6. Uneven Brake Pad Wear
If one of the hydraulic circuits in the brake master cylinder develops an issue, uneven brake pad wear may occur.
In this case, one set of brake pads will be more worn than the other as the one with hydraulic circuit problems won’t be functioning efficiently. This, again, can translate to vehicle weaving whenever you press the brake pedal.