How to Bleed the Air Out of a Master Cylinder on a Truck
The master cylinder is responsible for supplying pressure to the brake booster and forcing brake fluid into the brake lines. The master cylinder is designed as a series of seals and pressure chambers to distribute brake fluid as pressure is applied.
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Instructions
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1
Check the brake booster cap to make sure that the cap is on correctly. A loose cap can cause air to be mixed into the brake fluid and cause problems. Air bubbles in the brake lines can cause hydraulic pressure loss resulting in an accident due to brake failure.
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2
Remove the brake line caliper bolt with an open-ended wrench. These bolts are also known as Banjo bolts because they are hollow, a feature that allows fluid to pass through the bolt while keeping the brake lines secured to the caliper. Depending upon the make and model of the vehicle, Banjo bolts can range in size from 1/2 inch to 5/8 inch.
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3
Have someone pump the brake pedal with the brake line disconnected while you look for air bubbles coming out of the brake line. Pump the brake until a smooth stream of fluid comes out of the brake line. While the stream of brake fluid is flowing, reinsert the Banjo bolt into the caliper with the brake line attached. Drain all the fluid into a bucket or bottle and dispose of it according to local laws. Replace the old fluid with new fluid rather than reusing the old.
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4
Repeat Steps 2 and 3 on each brake caliper. Be sure to refill the brake fluid reservoir before you bleed each line. This will prevent air from getting into the lines again.
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Tips & Warnings
Air in the brake booster or lines is not uncommon.
Apply the parking brake and secure the vehicle with wheel chocks before beginning the procedure.
