Bleed and Flush Brake System

How To Bleed Car Brake System

How To Flush Car Brake System

Helpful Information

The brake fluid in your cars brake system is a hydraulic based fluid that is used to transfer force from the brake pedal to the brake caliper or wheel cylinder. The purpose of the brake system fluid change is remove moisture which contaminates the fluid and causes brake system failures. This service also replaces fluid that has been broken down by today’s complex ABS systems. Moisture is the leading cause of brake system operation failure. Brake fluid is subject to extreme pressure and heat so the boiling point of brake fluid is important. Higher boiling points (severe duty) and Anti-Lock braking systems require higher quality brake fluid; this fluid must also have a very low freezing point. There are several forms of brake fluid that are rated by the government for the various boiling points and other factors. These rating are DOT2, DOT3, DOT4 and DOT5. Distinctive ratings define the chemicals the fluid is produced with such as, mineral oil, ester glycol esters and synthetic oils. Many of these fluids are not compatible so make sure you add and flush your brake system with the manufacturers recommended brake fluid. Almost all brake fluid is corrosive and extreme care must be used when handling brake fluid.

If any brake fluid is spilled, flush thoroughly with water, this goes for human contact as well as spillage on your vehicles paint. Always add brake fluid from a sealed container and never allow moisture into the brake fluid. A brake system flush is used to remove any moisture and dirt out of the system and replace it with new fluid. After a flush is complete a full system bleed procedure is required, always check brake pedal operation after the work is complete, if normal brake pedal operation is not present DO NOT move vehicle until further inspection or repairs are performed and normal braking operation has resumed.

Common Problems

Stuck Bleeder Valve - The brake bleeder screw can be very tight, this is because all bleeder screws seal against a taper fit seat in the wheel cylinder, or caliper. When loosening a brake bleeder always spray WD40 or equivalent to aid rust removal then use a quality tool with little to no wear on it, 6 point wrench or socket is best.

No Fluid Flowing Out of the Brake Bleeder - This can be because the bleeder is not used very often so it can get filled with dirt and moisture clogging the passage. If this is the case open the plugged bleeder (with other 3 closed) and press the brake pedal down, this additional pressure from the other bleeders being closed will force the fluid out of the plugged bleeder. Once the bleeder has become unplugged finish the bleeding procedure until clean fluid is present. Then close the bleeder and release the brake pedal slowly.

Best Practices

• Always uses protective gloves, clothing and eyewear to guard against accidental spillage.

Step by step guide on how to bleed and flush and brake system. This articles pertains to most vehicles.

Difficulty Scale: 2 of 10

Tools and Supplies Needed

• Small wrench set
• Vacuum hose
• Brake fluid
• Protective clothing and gloves
• Shop towels
• Helper

Start with the car on level ground, engine OFF, lifted safely using jack stands.

Step 1 - Identify brake master cylinder components, brake fluid cap, brake master cylinder, fluid lines, and brake fluid level sensor. Inspect for any brake fluid leakage around the master cylinder and check for proper fluid level regularly. If leakage is present replace master cylinder immediately. 

Step 2 - Remove brake fluid reservoir cap and insert a brake fluid removal tool (turkey baster), remove as much brake fluid as possible, then refill the master cylinder with new fluid. Most cars use DOT3 or DOT4, but you should consult the cap on the master cylinder or a service manual.

Step 3 - Once the master cylinder is full loosen all four brake fluid bleeder screws on the brake calipers or wheel cylinders. Next, have a helper slowly press the brake pedal down completely, while holding the brake pedal down, close all four brake bleeder screws. Allow the brake pedal to slowly return to normal position, this will draw new fluid into the master cylinder body. Continue this procedure until the brake fluid is clean out of each bleeder, close all bleeders and refill the master cylinder to the proper level. (Note: Always keep proper fluid level in the master cylinder during this operation.)