A Guide to Break Booster and Master Cylinder

Auto Man Transmission

Junior member
  • Jul 5, 2023
    Your brake booster and master cylinder are like the unsung heroes of your car’s brakes. They make sure you stop safely and smoothly. But, like all good things, they can wear out over time. Keep an eye on them and replace them if needed. That way, your brakes will keep on doing their job properly, keeping you and your passengers safe and sound.

    Ever heard of a brake booster and a master cylinder? These are essential bits of kit in your car’s braking system. They’re the ones that help you stop when you press that brake pedal. But sometimes, they can go pear-shaped and cause a spot of bother. How can you tell if your brake booster or master cylinder is on the blink? And how do you give ’em a once-over?

    In this guide, we’ll run through how to check these parts and what to do if they’re giving you trouble.

    What’s a Brake Booster?​

    break booster

    A brake booster is like a helper that uses engine vacuum to make the brake pedal easier to push. It sits behind the brake pedal and connects to the master cylinder. When you put your foot down on the brakes, the brake booster gives the master cylinder an extra nudge, making the brakes more effective and taking the strain off your leg.

    What’s a Master Cylinder?​

    master cylinder

    The master cylinder is the gizmo that turns the force from your foot on the brake pedal into hydraulic pressure. It’s tucked away on the engine compartment’s firewall and hooked up to the brake lines going to the wheels. When you press the brake pedal, the master cylinder pushes brake fluid through the lines to the brake calipers or wheel cylinders, which then squeeze the brake pads or shoes against the rotors or drums, slowing down your motor.

    How to Suss Out a Dodgy Brake Booster​

    To check if your brake booster’s playing up, follow these steps:

    Switch off your car and pump the brake pedal a few times to release the vacuum from the brake booster.
    Keep the brake pedal pushed down and start your motor. If it sinks about an inch, all's well with the brake booster. If not, it could be faulty or there might be a problem with the vacuum hose.
    Listen out for a hissing sound inside the car when you press the brake pedal. That could mean a leak in the brake booster, especially if the noise changes when you're braking.
    If you spot any of these signs, it’s time to get your brake booster checked by a pro. A dodgy one can make your brakes less effective and up the chances of a prang.

    How to Check for a Bad Master Cylinder​

    To give your master cylinder the once-over, do this:

    Start your motor and let it idle. Firmly press the brake pedal and hold it. If it stays firm and doesn't sink, the master cylinder's likely sound. If it slowly sinks, though, the master cylinder could be on the blink – losing hydraulic pressure and letting brake fluid escape.
    Switch off your car and unscrew the master cylinder from the brake booster. Check behind it for any signs of brake fluid. If you see any, the master cylinder could be at fault, with a seal gone and brake fluid leaking out.
    Pinch off or cap the brake hoses or lines leading to the calipers or wheel cylinders. Firmly press the brake pedal and keep it down. If the pedal still sinks, the master cylinder's likely had it. If it stays firm, though, the issue might lie with the brake lines or the calipers or wheel cylinders.
    If you reckon your master cylinder’s on the blink, it’s best to replace it pronto. A duff one can spell disaster for your brakes, leading to a nasty accident. And don’t forget to give your brake fluid a regular flush to ward off rust and damage to the master cylinder and other brake bits.

    If you’re in a trouble with your brake booster or master cylinder, Don’t wait. Visit your nearest repair technician. Get the expert inspection.

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