When the brakes on your 1973 Chevy C60 truck wear very thin, it's possible for the level of brake fluid in the system to get low enough that air can be drawn in through the master cylinder. When this happens, your brakes will feel weak and squishy even after the brake pads are replaced because the air in the brake lines can be compressed far more easily than the brake fluid that's supposed to fill them. This problem can be resolved by bleeding your brakes.
Tools Used: Assistant, Jack, Jack stands, Penetrating oil, Lug wrench, Turkey baster, Lint-free cloth, Box wrench, Plastic aquarium tubing, Clear container, Brake fluid, Tape
Bleed the Brakes
Spray penetrating oil on the bleeder valve screws. These are on the sides of the wheel cylinder bodies, mounted to the brake backing plates on each wheel. Let the penetrating oil sit for several hours. Raise the vehicle with a jack and support it safely on jack stands. Remove all four wheels.
Lift the hood and prop it open. Remove the cover from the master brake cylinder on the right side of the engine compartment as you face the vehicle. Use a turkey baster to suck up as much of the old brake fluid from the reservoir as possible. Clean the reservoir with a lint-free cloth.
Use a box wrench to loosen the bleeder valve screw on the right rear wheel, but don't open it. Place a length of plastic aquarium tubing over the end of the bleeder valve and place the other end of the tube in a clear container with a couple inches of clean brake fluid in the bottom. Make sure the end of the tubing is submerged in the brake fluid to prevent air being sucked into the system on that end.
Fill the master cylinder reservoir with clean, fresh brake fluid and replace the cover. Stick a piece of tape across the pin at the end of the combination valve, found behind the master cylinder on the brake line, to hold the pin in the open (pressed in) position.
Tell your assistant in the truck's cab to press the brake pedal down. While the pedal is depressed, open the bleeder valve screw a quarter turn so that old brake fluid trickles out through the plastic tubing. When it stops flowing, close the bleeder valve and direct the assistant to release the brake pedal. Repeat this step until clean brake fluid with no bubbles flows from the valve. Check the level of the brake fluid in the master cylinder reservoir frequently and refill it as necessary.
Repeat Steps 3 through 5 with the other wheels. After the right rear wheel, do the left rear, then the right front, and finally the left front.
Refill the master cylinder reservoir one final time. Close the master cylinder. Remove the tape from the pin on the combination valve and close the hood. Remount the wheels and lower the truck to the ground.
Tips & Warnings
Never let the master cylinder reservoir fluid level fall below the halfway mark. Doing so may allow more air to enter the brake system.
Use only clean brake fluid from unopened bottles. Opened bottles of brake fluid have a very short shelf life.
If the penetrating oil is not sufficient to loosen the bleeder valve screws, try tapping them with a hammer to dislodge corrosion.
Failure to service the brake system properly may result in dangerous brake problems or brake failure.
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