Hi Paul, I am an avid reader of your car advice. It’s been helpful specifically to me. My Mercedes C class brakes are not working well. The brake pedal sinks when I step on it and the car delays to stop. A mechanic in town has replaced all the brake pads and topped up brake fluid but the problem persists. I might cause an accident in traffic jam or if I brake suddenly. What could be the problem? Alice Namukasa
Hello Namukasa, your Mercedes brake system most likely has a leakage of brake fluid pressure in the hydraulic system. From your description and recent repair history your brake system feels spongy after replacing brake pads.
The mechanic had to top up brake fluid. Ordinarily your brakes should feel firm when applied. There is a need to inspect the brake master cylinder and brake lines to all the four brake calipers for brake fluid leakage.
The braking system relies on the brake master cylinder to use brake fluid to pressurize the system. Overtime ageing brake fluid accumulates a small percentage of moisture which degrades it.
The brake fluid will not effectively carry out its performance enhancing (hydraulic pressure) and lubrication roles.
The brake fluid protective functions such as preventing overheating and damage of master cylinder piston, callipers and hose seals or corrosion damage of all the brake system components are also reduced with age or leakage.
A subsequent accumulation of vacuum pockets in the brake fluid lines prevents prompt buildup of hydraulic pressure and poor brake performance. Going forward, the leaking or damaged brake system components should be identified and replaced.
The ageing brake fluid should all be replenished (serviced) using the Mercedes recommended electronic brake power bleeder tool.
This will renew all the brake fluid and prime the brake system (bleed) to eliminate pockets of vacuum. The bleeder tool effectively bleeds the system and prevents accidental damage of the new master cylinder unit. Your normal brake performance should be restored thereafter.