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| Common Brake Problems 1. Spongy Pedal (Air – Bleed from the furthest bleed screw from the master cylinder and work in . Bleed screws up) (Caliper brackets not square to rotor causing caliper deflection) (Rubber brake lines deflecting) (Brake fluid too hot) (Pedal ratio too high) (Silicone brake fluid – highly compressible) 2. Low Pedal – Have to pump the pedal to get it hard (Master cylinder too low causing fluid drain back to reservoir – install 2 lb. Residual pressure valve or move reservoir higher than calipers) (Warped rotor causing piston knock back) (Excessive rotor runout causing piston knock back) Excessive piston retraction – install square seals) 3. Low Pedal – Won’t Pump Up (Bad caliper seals, leaking) (Leak in hydraulic system) (Balance bar too far off center) (Badly worn pads) 4. Pedal Hard – Car Won’t Stop (Master cylinder too large, too much volume) (Pedal ratio too small – Insufficient pressure on master cylinder) (Glazed rotors) (Glazed pads) Basic Disc Brake Maintenance 1. Inspect for excessive rotor run-out. 2. Inspect for warped rotors. 3. Inspect for cracked rotors. 4. Flush brake fluid before each race. 5. Inspect pads for excessive taper or wear. 6. Replace caliper seals when you replace pads. 7. Inspect for leaking around seals. 8. Inspect for any loose bolts. Formulas, Calculations And Trouble Shooting Answers The following information contains simple formulas, examples, and trouble shooting answers to common disc brake problems that every racer experiences. We hope this will come in handy during the set-up and maintenance of your high performance disc brake system. Basic Formulas: Calculating the Square Inches of Caliper Piston Area Pi times (radius of the piston squared) times (half the number of pistons). Example: Calculate the square inches of piston area of a caliper with four pistons 1.75" each. Pi=3.1417 Radius of a 1.75" piston = .875" 3.1417 x (.875 x .875) x 2 = 4.81 sq./in. of piston area Calculating the Ratio of a Brake Pedal Divide the length from the pivot point to the push rod (B) into the length from the pivot point to the center of the foot pad (A). Example: (B) Length from pivot point to push rod = 2.0" (A) Length from pivot point to center of foot pad = 14.0" 14 divided by 2 = 7 Pedal ratio = 7:1 Calculating Master Cylinder Line Pressure Pressure = (Leg force on the pedal) x (Pedal Ratio) divided by (Master Cylinder Piston Area). Example: Calculate the line pressure of a 1" bore master cylinder using a 7:1 ratio pedal. Leg Force (Effort) = 150 lbs. Pedal Ratio = 7:1 Square Inches of Area (1" Bore Master Cylinder) = .785 150 x 7 divided by .785 = 1,337 psi
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