There aren't many of you who haven't bled a Mustang's braking system while replacing or repairing your own brakes. Here's why you should bench-bleed a master cylinder prior to installation. Bench-bleeding off the car primes the bore with fresh brake fluid, eliminating air prior to installation to prevent the air from entering your Mustang's brake hydraulic system. It also prevents master cylinder piston jamming because you can observe the process hands-on in a vice.
You can bench-bleed your master cylinder using brake hydraulic lines or by purchasing a master cylinder bench bleeding kit from a local auto parts store.
1 Pour fresh brake fluid...
1 Pour fresh brake fluid into each reservoir, keeping air bubbles to a minimum. Wait for the fluid to stabilize and become air-free before beginning the bleeding process. Make sure both tube ends are submerged in fluid once the reservoirs are full and both fittings are tight.
2 Using a Number Three Phillips-head...
2 Using a Number Three Phillips-head screwdriver, slowly depress the master cylinder piston and observe the fluid and bubble activity. Push until the piston just touches bottom, but don’t go too far. Back off and do this again until the fluid flows bubble free. Keep in mind that if you depress the master cylinder piston too far, it can jam and stay jammed. So exercise caution. Install the lid and cap ports. Remove the caps only when you’re ready to install the master cylinder. When it’s time to bleed the brakes, begin at the brake farthest away and take it one by one as you work your way closer. Make sure the master cylinder is serviced with fluid at all times. MM