Electric vacuum pumps like this one from Master Power can be the cure for a hard pedal if
Solution 3: Optimize Pedal Ratio
Measure pedal ratio and revise geometry to increase leverage. Many factory brake pedals come with two holes drilled in them, one for manual and one for power brakes. When switching between the two systems, it is important to use the correct pushrod hole. The general rule of pedal ratios with top pivots is: The hole closest to the pivot point makes more pressure but will need to travel farther to move the same volume of fluid, while the hole farthest away from the pivot point will make less pressure but will move more fluid per stroke. You can experiment with pedal ratios by drilling different holes, but pay attention to the pedal/pushrod geometry and don't go "over center." Wilwood Engineering says that a 6:1 pedal ratio is an ideal starting point. Master Power recommends a 4:1 for power brakes and 5:1 for manual brakes.
Problem: Rear Brakes Seem To Be Doing All The Work
This problem is common in cars which have rear disc brakes swapped in from a different car.
Cause: Rear Caliper Piston Area Greater Than Front
Brake balance front to rear can never be correctly adjusted when the rear piston area is larger than the front. No adjustable proportioning valve (or number of valves employed) can correct this problem. For proper performance the front caliper piston area must be at least 25 percent greater than the rear piston area, preferably closer to 40 percent (for reference; a stock '93-97 Camaro has a front piston area 55 percent greater than its rear).
Performance Friction's Z-Rated hi-temp brake fluid is great for street and occasional trac
Solution: Measure all caliper piston diameters and change front or rear calipers (and master cylinder if necessary) to achieve appropriate front-to-rear differential
Calculating AREA of caliper and master cylinder pistons.AREA = 3.1416 x (RADIUS x RADIUS)
Determine the area of a 15/16-inch (0.9375) bore master cylinder.
First establish the radius, which is half the diameter: 0.9375 / 2 = 0.4687So plug 0.4687 into the formula and get: 3.1416 x (0.4687 x 0.4687) = 0.6902 is the piston area of a 15/16-inch bore
Determine the area of a non-opposed two-piston, 1.5-inch diameter caliper.*Solve for area of each piston first, and then add both areas together.
Radius = 1.5 / 2 = 0.753.1416 x (0.75 x 0.75) = 1.7671 x 2 = 3.5342 is the area for both pistons combined.
Note: When calculating the area of a caliper with multiple, opposing pistons, Baer determines the area of only one bank of pistons for comparison purposes.
Divide the area of the master cylinder by the area of one front caliper to find your percentage.0.6902 / 3.5342 = 19.5%
When designing a brake system always shoot for a figure between 12-19 percent as a starting point, but that's only the beginning-final tuning on the road may determine a different size master cylinder is needed.
Bleeding Can Make You Stop Better
Bleeding brakes is not done with pressure: it is purely a function of moving fluid through the system. The object is to displace air, not to see how far you can squirt fluid out of the caliper! Enlist someone to help you bleed the brakes. Make sure they also read these instructions carefully and understand the goal.