When replacing braking components, such as calipers, brake lines, or master cylinders, or whenever a complete brake fluid flush is performed, it is important to bleed the air out of your braking system. Air in the lines causes multiple problems, such as a soft pedal, reduced braking performance, and contaminated brake fluid.
Because air can be compressed and the column of brake fluid cannot, any air bubbles will act as a spring in the brake line and be the cause of a spongy pedal. Brake fluid can also absorb moisture from the air, as well as dirt and wear particles, becoming contaminated over time and potentially lowering the brake fluid’s boiling point to a dangerous level, possibly leading to brake system failure. To avoid this, brake fluid should be replaced every two to three years.
Before you begin bleeding your brakes, it is important to top the master cylinder off with fresh brake fluid (hopefully you’ve just replaced that dirty stuff you’ve been driving with for the past year). You’ll also want to remove the wheels and tires to gain access to the calipers. Next, you’ll need a partner who has the ability to stay focused, listen to direction, and most importantly the ability to pump the pedal.
With your partner in the driver seat, locate the bleeder bolt on the backside of the caliper furthest from the master cylinder. Using an empty (and dry) water bottle and some tubing, put a little fresh brake fluid in the bottle. The tubing will fit over the bleeder on one end and sit underneath the surface of the brake fluid in the bottle on the other.
Next, you will instruct your helper to pump the brakes to get a firm pedal. Once the pedal is firm, your helper will hold the pedal down while you open the bleeder on the passenger rear caliper. With the bleeder open and your helper still holding the pedal, it will sink to the floor, forcing air from the line. Close the bleeder, repeating this process until nothing but clear fluid exits the line.
When you are satisfied that the first caliper is free of air, it is time to move to the driver’s rear, passenger front, and driver’s front caliper—in that order, until all of them have been bled. Be sure to constantly monitor the brake fluid level in the master cylinder, topping it off with fresh brake fluid when needed.
It is not uncommon to still feel a slightly soft brake pedal feel after one round of bleeding. If that is the case, repeat the procedure. Once your pedal returns to normal, you are all finished and sporting a new sense of accomplishment and a firm brake pedal.