Brake Fluid
You bleed your brakes to remove moisture that entered the system. Brake fluid needs to be replaced periodically because brake fluid will absorb moisture over time. This occurs whether a vehicle has been driven 60,000 miles, or has been sitting in a garage for a year. Fluid contamination is a function of time and humidity and has nothing to do with the mileage driven. Moisture enters the brake system through seals and through microscopic pores in the hoses. Moisture enters the system every time the fluid reservoir is opened, which is a good reason not to open it unnecessarily.
To remove air bubbles that have entered the system because of a leak or because the fluid level got too low. The air must be removed because it is compressible and will result in a soft, “spongy” brake pedal.
First, always start at the corner furthest from the driver and work your way towards the driver/master cylinder (right rear, left rear, right front, left front.), just remember farthest to closest. Then, find the bleeder screw (bleeder valve) on the rear caliper. Attach a piece of clear tubing to the nipple of the bleeder screw. Place the other end of the hose into the disposable bottle. Then take a wrench and place it on the bleeder screw. Place the bottle for waste fluid on top of the caliper. Hold the bottle with one hand and grasp the wrench with the other hand.
Next, have your assistant apply the brake pedal and hold down firmly. Then open the bleed screw ¼ turn to release the fluid into the waste line. NEVER have the driver release the brake pedal while the screw is open, make sure to CLOSE the screw first and then have the driver release the brake pedal. Inspect the fluid within the waste line for air bubbles. Continue the bleeding process until air bubbles are no longer present. Be sure to check the brake fluid level in the reservoir after bleeding each wheel, make sure to keep the fluid level at the MAX line. Then, go on to the next corner and repeat all steps.
Next, spray with brake cleaner and then wipe down the entire area until dry. DO NOT SPRAY BRAKE CLEANER ON ANY RUBBER OR PLASTIC PARTS. Leaving the area clean and dry will make it much easier to spot leaks. Test the brake pedal for a firm feel, and if all the steps were followed then you are done bleeding your brakes. Discard of any and all used brake fluid properly and responsibly.
Brake fluid is hygroscopic, meaning it absorbs water. When new from the bottle, it can be considered “dry” with a higher boiling point. Over time, brake fluid absorbs water lowering its boiling point to the “wet” level. Changing brake fluid removes water from the brake system and is extremely important. Change your brake fluid at least every two years … much more often for cars that see track use. For street cars, wet boiling point numbers are more important than dry because the fluid stays in your car for a long time (change it at least every two years). After months of exposure to humid air and changing climate conditions, brake fluid performance is closer to the wet boiling point than the dry boiling point. When brake fluid boils, it turns into vapor and forms air bubbles. This creates a “soft pedal” and requires excessive pedal travel to apply the brakes properly. Do not confuse this with “brake fade”. Brake fade occurs when the brake compound gets too hot from prolonged braking or improper bedding. Brake fade requires greater and greater pedal effort to stop the vehicle; boiling fluid increases pedal travel and makes the pedal feel soft. Due to the extreme temperatures that high performance brake systems operate at, standard brake fluids are not recommended for track use. Carbotech™ Performance Brakes does not sell and does not recommend silicone based brake fluid with any of its products.
Neither Carbotech Performance Brakes nor AP Racing markets silicone brake fluids nor recommends their use with any braking system. The high price of silicone fluids does not produce higher performance in hard driving or even normal road use. Rather, use of silicone fluids leads to issues.
Virtually all of the problems with silicone brake fluids reflect certain properties of silicone fluids identified by us over many years and recently ratified in SAE publications. Those properties are specifically: high ambient viscosity; high air absorption; high compressibility; low lubricity; and immiscibility with water. Research has shown that these properties of silicone fluid result in “spongy” pedal, sudden loss of braking, and/or “hanging on” of brakes.
Carbotech’s AP Racing glycol based fluids do not exhibit the adverse properties of silicone fluids. The recently introduced Formula DOT 5.1, which exceeds the performance criteria of DOT 5 (Silicone), is suitable for all conditions likely to be encountered in modern driving conditions.
Brake fluid can absolutely damage brake pads. That’s why it is so vital that the hydraulic system is in good working order with no leaks.