Many 1971 Chevrolet half-ton trucks came with manual brakes. This means that the brake master cylinder push rod is connected directly to the brake pedal, a set-up which requires more pedal effort to apply the brakes than a vehicle that has power brakes. Adding power brakes to your truck can be done by installing a brake booster in between the master cylinder and the brake pedal. With the right parts and a few tools, your 1971 C10 truck can have power brakes.
Removing the Existing Master Cylinder
Remove the split pin from the large pin that attaches the bracket on the upper portion of the brake pedal to the master cylinder push rod under the dashboard with a pair of pliers. Discard the split pin. Slide the large pin out of the brake pedal bracket and the push rod and place it aside.2
Open the hood and remove the master cylinder reservoir cap. Siphon the brake fluid from the reservoir with a syringe. Twist off the two brake lines from the master cylinder, using a tubing wrench placed on the brake line fittings.3
Remove the retaining bolts from the master cylinder mounting flange with a socket and ratchet. Slide the master cylinder straight out from the firewall until the push rod clears, then remove it from the engine compartment.
Brake Booster Installation
Position a brake booster adapter plate against the firewall, lining up the original master cylinder mounting holes with the holes in the bracket. Bolt the adapter to the firewall using these holes. Drill through the remaining holes in the bracket with a 3/8-inch drill bit and a power drill to create mounting holes in the firewall for the brake booster.5
Place a rubber booster-to-firewall gasket over the large hole in the center of the adaptor plate. Position the brake booster against the firewall, sliding the booster push rod through the gasket. Line up the holes in the booster mounting bracket with the newly drilled holes in the adapter plate and bolt it into place, using a socket and a ratchet.6
Line up the hole at the end of the booster push rod, inside the truck cab under the dashboard, with the hole in the brake pedal bracket. Insert the large pin through the hole. Insert a new split pin through the small hole in the end of the pin. Bend the protruding end of the pin with pliers to keep it from working out of the hole.
Installing the New Master Cylinder
Place the master cylinder on a bench or work area. Connect the two tubes of a bench-bleeding kit -- available from most auto parts stores -- to the fittings on the bottom of the cylinder where the brake lines would normally attach and tighten them with a tubing wrench. Place the opposites ends of the tubes into the master cylinder reservoir.8
Fill the reservoir with brake fluid. Move the master cylinder push rod in and out until air bubbles stop coming from the ends of the hoses in the reservoir. Add fluid to the reservoir during this process as needed to keep it full. Remove the bench bleeding kit from the cylinder. Replace the reservoir cap.9
Keep the master cylinder level. Line up the holes in the mounting flange of the cylinder with the threaded studs on the booster. Push the cylinder up against the booster. Place nuts on the studs and tighten them with a socket and ratchet. Attach the brake lines to the master cylinder and tighten the fittings with a tubing wrench.10
Start the engine and pump the brake pedal until it feels firm, indicating that the booster and master cylinder are working properly. Stop the engine and check that all air has been removed from the brake fluid in the master cylinder and that the brake booster is connected correctly, if the brake pedal remains soft.