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How do I bleed the brakes?

How do I bleed the brakes?

A properly functioning brake system is essential for safe driving. Keeping the brakes in good condition is the responsibility of every driver.

Sometimes, when the brake fluid level in the master cylinder reservoir drops very low, air bubbles can enter the circuit and reduce the efficiency of the braking system. When you step on the brake pedal, it offers almost no resistance and feels soft. You need to bleed the air out of the circuit to restore your car's stopping power.

Let's find out what's causing the air in the system. In this article, we'll explain the proper procedure for bleeding a brake system.

The main causes of air in the system are

  • Low fluid level in the reservoir: Ambient air can be drawn into the system.
  • Rubber component wear: When exposed to moisture, dust, and road chemicals, wheel cylinder (or caliper) seals lose their elasticity and begin to fail. Over time, hoses also begin to crack.
  • Failure to change the brake fluid in time: The structure of the hoses through which the brake fluid circulates is porous, so even a small amount of water can enter the system. It then mixes with the brake fluid, lowering its boiling point. The problem is that the fluid can then boil over during repeated braking, such as when driving on a winding road. This boiling process creates steam and air bubbles in certain parts of the pipes and hoses.
  • Leaky clamps and connectors: Over time, clamps and connectors loosen due to vibration from driving on bumpy roads, allowing air to enter.
  • Repairs:When replacing pistons, cylinders, pipes or hoses, be sure to deflate the brake system immediately. Removing these components will allow air to enter the line and remain there after reinstallation.

How do I bleed the brakes?

  • Step 1: Unscrew the reservoir cap. This is usually located under the hood of the car. It's a light-colored reservoir protected by a black cap and connected to the brake pedal.
  • Step 2: Drain the used fluid.  Use a spray nozzle to suck up as much brake fluid as possible and drain it out of the system.
  • Step 3: Clean the reservoir.  After the fluid is drained, use a clean, lint-free cloth to remove any accessible residue from the reservoir.
  • Step 4: Fill with brake fluid to the "Max" mark. You'll see the fluid level rise as you fill the reservoir. You'll need to check it periodically to prevent air from entering the system through the reservoir during bleeding.
  • Step 5: Ask an assistant to depress the brake pedal several times in a row, then depress it all the way. The goal is to circulate new fluid through the circuit.
  • Step 6: Meanwhile, loosen the bleed screw to allow fluid to circulate in the hose.
  • Step 7: Ask your assistant to fully depress the pedal.
  • Step 8: Watch the fluid come out of the bleed screw. It will contain bubbles.
  • Step 9: Tighten the bleed screw. Your assistant can then release the pedal.
  • Step 10: Repeat this procedure 4-5 times for each brake mechanism.
  • Step 11: Don't forget to check the fluid level in the reservoir and fill it to the "Max" mark.
  • Step 12: While doing this, make sure the fluid doesn't drip onto the car's bodywork, as it contains ingredients that can damage the paint. Also make sure it doesn't run onto the brake pads. If it does, replace them.

When should I bleed the brakes?

If not properly bled, the hydraulic braking system will become less efficient or even inoperable. Over time, air bubbles can enter the system and affect the quality of the brake fluid. This can eventually lead to brake failure. What's more, the fluid can easily boil under the influence of heat, causing the brake pedal to become soft. For all these reasons, it is important to bleed the brake hydraulic system regularly. This should be done every 2 years or 20,000 km. However, this is only a guideline. Remember to bleed and check the entire system at the first sign of failure.

How do I bleed the brake lines without assistance?

If you don't have anyone to help you, it's still possible to do this procedure yourself. There are several ways to do this:

  • You can bleed the lines the same way you would with an assistant, using a gas cylinder to hold the pedal down. To do this, you can temporarily remove one from the hood or trunk door. To make things easier, you can buy a special brake bleeding kit. This includes fittings, adapters, hoses, and a bleed reservoir. This is very handy if the reservoir is equipped with a strong magnet, as it allows you to attach it to any part of the car's body and prevents the reservoir from turning over and spilling fluid.
  • Flushing with a special vacuum pump. The procedure is as follows: Fill the reservoir with working fluid to the maximum level. Connect the pump hose to the bleed screw on the wheel cylinder (caliper) you're working on. The fluid sucked in by the pump is collected in a special reservoir and the air is eliminated.
  • Bleeding by building up pressure in the reservoir. You may need several devices: syringes, small manual compressors, and other tools. Their working principle is based on the introduction of compressed air or brake fluid into the expansion tank, which circulates the fluid in the line and replaces the process of pressing on the pedal. The rest of the procedure is similar to normal bleeding: air-bubbled brake fluid is bled through the hose connected to the bleed screw of a wheel cylinder (caliper).

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