The original factory brake system on the early Mustang was a four-wheel drum, either manual or power boost, or a front-wheel disc and rear-wheel drum system. The 1966 Mustang had this system with a single-piston, so-called "fruit-jar," master cylinder on the firewall. The fruit-jar is comprised of 15 parts. Rebuild kits are readily available, and the rebuild can be completed in a couple of hours.
Tools Used: Wheel chocks, Safety glasses, Mechanic's gloves, SAE flare nut wrenches, SAE 3/8-inch ratchet and socket set, Compressed air, Internal spring clip pliers, Brake cylinder hone, Variable speed drill, Brake cleaner, Cast Blast paint, Silver Cad paint, Gold Cad paint, Aluminum pie plate, Small container, Brake fluid, Master cylinder rebuild kit
Rebuild Master Cylinder
Park the car on a level surface and chock the rear wheels. Disconnect the bolt from the brake pedal through the master cylinder push rod under the dash. Move to the firewall and disconnect the brake line from the front of the master cylinder. Catch the brake fluid in an appropriate container and do not get any on the paint. Remove the two nuts holding the master cylinder to the firewall. Take the master cylinder to a clean work surface.
Remove the rubber boot over the push rod. Using internal spring clip pliers, remove the spring clip. The internal spring should push out the piston; if not, use compressed air through the brake line fitting. Place a rag over the piston opening to prevent the piston from flying out as a projectile. Remove the master cylinder cap, brake switch and the brake line adapter fitting. Remove the following internal parts in order: check valve seal, one-way check valve, spring, piston cup, piston and clip.
Clean all the parts with brake cleaner. Use the cylinder hone on a variable speed drill to remove any pitting on the inside of the master cylinder, applying even strokes up and down the cylinder. Lubricate the hone with brake fluid and add more brake fluid after every couple of strokes. Rinse the master cylinder clean with brake cleaner. The bore should be smooth, without any pits.
Clean the master cylinder again with brake cleaner and let it dry, then paint it with Cast Gray paint. Clean and paint the brake switch metal portion with Silver Cad. Clean and paint the master cylinder top with Gold Cad. Clean and paint the push rod with Silver Cad. Clean the brass fitting until it is shiny.
Pour fresh brake fluid into a pie plate and coat the check valve seal, check valve, spring and piston. Coat the inside cylinder bore with brake fluid. Install the new components in the following order: check valve seal, check valve (correct direction), spring, piston cup (cup towards brake line fitting) and piston (seal towards push rod). Install a new spring clip. Replace the rubber boot and push rod. Reinstall the brake line fitting and brake switch.
Reinstall the master cylinder on the car in reverse order of removal. Fill the master cylinder with brake fluid. Bleed the brakes starting with the passenger's side rear wheel. Finish bleeding the brakes on the driver's side front wheel. Take the car for a test-drive.
Tips & Warnings
Always wear safety glasses.
Be careful around brake dust. Old brake shoes have asbestos in them. Do not blow out brake dust. Wash out the brake dust with brake cleaner, collect the fluid then discard in a plastic container.
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