Do you bleed brakes with the master cylinder open or closed?
When it comes to brake maintenance, one of the most common questions is whether to bleed brakes with the master cylinder open or closed. Understanding the correct procedure is crucial for ensuring your vehicle's braking system functions effectively and safely. In this article, we will explore the best practices for bleeding brakes and the implications of the master cylinder's position during the process.
The Importance of Proper Brake Bleeding
Brake bleeding is essential for removing air bubbles from the brake lines, which can lead to a spongy brake pedal and reduced braking efficiency. Air in the brake lines can compromise the hydraulic pressure needed for effective braking, making it vital to perform this task correctly.
Should the Master Cylinder Be Open or Closed?
When bleeding brakes, it is generally recommended to keep the master cylinder closed. Here’s why:
- Prevents Contamination: Keeping the master cylinder closed helps prevent dirt and moisture from entering the brake fluid, which can lead to corrosion and other issues within the braking system.
- Maintains Fluid Level: An open master cylinder can lead to a drop in brake fluid levels, which may introduce more air into the system, counteracting the purpose of bleeding.
- Consistent Pressure: A closed master cylinder helps maintain consistent hydraulic pressure during the bleeding process, ensuring that air is effectively expelled from the brake lines.
Steps for Bleeding Brakes
Here’s a quick overview of the steps to bleed your brakes effectively:
- Ensure the vehicle is on a level surface and secure it with wheel chocks.
- Check the brake fluid level in the master cylinder and top it off if necessary.
- Start with the wheel farthest from the master cylinder (usually the passenger rear wheel).
- Have an assistant pump the brake pedal several times and hold it down.
- Open the bleeder valve on the brake caliper to release fluid and air, then close it before your assistant releases the pedal.
- Repeat the process until no air bubbles are visible in the fluid.
- Move to the next wheel and repeat the process
Frequently Asked Questions
Will air work itself out of brake lines?
The only way to remove the air from the brake lines is to do it manually, as the air won't dissipate on its own. We can certainly perform this process at our service shop, but you're also welcome to try the process on your own, too!
Will a master cylinder eventually bleed itself?
You might think that the air will find its way out, but a master cylinder cannot self-bleed. The trapped air must be manually bled out through a controlled process, even if there are just a few small bubbles.
How to bleed air out of master cylinder?
The easiest way to bleed just the master cylinder is to have someone pump the brakes in the car, then hold the pedal down. Now you, the technician crack open one of the brake lines on the master cylinder to let the trapped air out. Don't open it all the way, close it as fast as you can.
What not to do when bleeding brakes?
The one thing that we shouldn't do when bleeding brakes is pump the pedal and then open the screw. Pumping the pedal can cause aeration of the fluid in the reservoir because of the two little jets of fluid that push back when we first hit the pedal.
Does the master cylinder need to be open to bleed brakes?
During brake bleeding, the master-cylinder cap should be left unscrewed but still in place atop the reservoir. Each brake must be bled in the correct sequence. Generally, you bleed the brake most distant from the master cylinder first, but some cars require a different order.
What is the correct order to bleed brakes?
The order on most cars begins with the passenger rear brake first, then the driver rear, then the passenger front and finishing with the driver front.
How do you get air out of a master cylinder?
The easiest way to bleed just the master cylinder is to have someone pump the brakes in the car, then hold the pedal down. Now you, the technician crack open one of the brake lines on the master cylinder to let the trapped air out. Don't open it all the way, close it as fast as you can.
How do you get air out of a cylinder?
Bleeding a Hydraulic Cylinder
- Move the air to the top of the cylinder for effective release.
- Extend the cylinder fully and leave it in this position to allow the air to rise.
- Partially close the cylinder when all the air has risen to the top of the cylinder.
- Open the bleed valve for the air to escape.
How do you release oxygen from a cylinder?
Open the valve slightly and verify the cylinder is free of oxygen charge. Do not remove the valve from cylinders containing any charge (pressure). Secure the cylinder, use a wrench that fits the valve body and manually supply enough force to break the valve free from the cylinder.
Do you leave the master cylinder cap off when bleeding brakes?
You need to leave the cap ON the master cylinder when bleeding the brakes at the wheel cylinders or at the Master Cylinder. You are forcing the fluid from the reservoir to the bleeders. Air will go first, then the fluid. If you have the cap off, there's a chance you'll just push the fluid back up out the opening.
