Why is there still brake pressure loss after replacing the master cylinder?
2 Answers
Brake pressure loss after replacing the master cylinder may be caused by poor piston sealing in the master cylinder or wheel cylinders, or a rupture somewhere in the brake lines leading to oil leakage and pressure loss. Here is some information about brakes: 1. Definition: As the name suggests, it is a mechanical braking device that can reduce vehicle speed, also known as a decelerator. 2. Operation: Simply put, the car brake pedal is located below the steering wheel. Pressing the brake pedal causes the brake linkage to be pressurized and transmitted to the brake shoes on the brake drum, which then clamp the brake disc to slow down or stop the vehicle. 3. Application types: The manual brake in cars is located next to the gear shift and is connected to the brake lever. Common examples also include bicycle brakes, which use frame-mounted rod brakes or disc caliper brakes for deceleration.
I think there are many reasons why the brake system still loses pressure after replacing the master cylinder. A common issue is that there is still air trapped in the brake system. Since the master cylinder was replaced, the new part might have introduced air during installation, especially if the tubing connections aren’t tight or the bleeding process wasn’t thorough. Air bubbles in the system can make the brake pedal feel soft and cause pressure loss. Another possibility is a leak in the brake lines themselves, such as cracked, aged hoses or loose fittings. Even with a new master cylinder, brake fluid could be leaking elsewhere, preventing pressure buildup. Additionally, the wheel cylinders or calipers might be faulty—worn piston seals could allow fluid to leak when the brakes are applied. Less commonly, issues like a faulty ABS module or a damaged proportioning valve could also be the culprit. I’ve also seen cases where poor-quality brake fluid with high moisture content corroded components. Don’t try to fix this yourself—it’s a safety-critical issue. It’s best to take the car to a professional shop immediately for a thorough brake bleeding and pressure test to avoid accidents on the road.
