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  • LOW PEDAL (Excessive pedal travel to apply brakes)
    • Air in hydraulic system - bleed hydraulic system thoroughly.
    • Brake shoes need adjusting.
    • Low brake fluid level - fill reservoir to proper level.
    • Poor quality brake fluid (low boiling point) - replace with approved fluid.
    • Broken front or rear hydraulic line (dual system master cylinder) replace hose.
    • Soft or weak hydraulic hose (expanding under pressure) - replace hose.
  • SPONGY BREAK PEDAL (Springy sensation to pedal upon application)
    • Air in hydraulic system - bleed system thoroughly.
    • Brake shoes need adjusting.
    • Poor quality brake fluid (low boiling point) - replace with approved brake fluid.
    • Soft or weak hydraulic hose (expanding under pressure) - replace hose.
    • Faulty check valves in master cylinder - repair master cylinder.
  • HARD PEDAL (Excessive pedal pressure needed to stop vehicle - pedal is high - but hard - on first pump. NOTE: If pedal must be pumped once or more before the pedal is received - refer back to low pedal sensation.
    • Vacuum hose collapsed (can be internal and not show on outside). Replace vacuum hose.
    • Loose or plugged vacuum fittings - repair or tighten fittings.
    • Cracked or broken plastic hub - replace unit.
    • Engine does not develop enough vacuum - tune up required.
    • Faulty vacuum check valve - replace faulty check valve.
    • Kinked, collapsed, dented or clogged hydraulic lnes, hoses or connections - repair or replace faulty part.
    • Swollen master cylinder cups (by fluid contamination) - flush system with alcohol to remove contaminated fluid and replace cylinder.
    • Restricted air filter or manual brake boot is installed (boot without air inlet holes) - replace air filter or boot.
    • Damaged diaphragm - replace unit.
    • Damaged valve rod and plunger assembly - replace unit.
    • Binding pedal linkage - free up and lubricate.
  • FADING PEDAL (A falling away of pedal under steady foot pressure)
    • Loose hydraulic connection; ruptured or damged hoses or lines (causing leakage) - repair or replace faulty part.
    • Worn or damaged master cylinder cups or master cylinder bore - replace unit.
    • Cracked master cylinder castings - replace unit.
  • PEDAL KICK BACK
    • Hydraulic valve seats damaged by dirt or fluid contamination - flush system with clean, heavy duty brake fluid and replace unit.
  • PEDAL APPLIES BY ITSELF
    • Cracked or broken hub - replace unit.
    • Damaged internal valve - replace unit.
  • BRAKES TOO SENSITIVE
    • Internal push rod not adjusted out to master cylinder piston. Adjust screw out until it touches (but does not apply) master cylinder piston.
    • Damaged reaction valve - replace unit.
  • DRAGGING BRAKES (Slow or incomplete release of brakes)
    • Hydraulic system contaminated with dirt causing check valves or pistions to stick. Flush system with clean heavy duty brake fluid.
    • Faulty check valves in master cylinder - repair or replace cylinder.
    • Swollen cups on master cylinder (by fluid contamination) - flush hydraulic system with alcohol to remove contaminated fluid and replace unit.
    • Kinked, collapsed, dented, or clogged lines, hoses or connections - repair or replace faulty part.
    • Broken return springs- replace unit.
    • Binding pedal linkage - free up and lubricate.
  • BRAKES WON'T RELEASE
    • Medium duty trucks with power brake mounted on the frame underneath the vehicle: Be sure master cylinder on the firewall has been replaced or completely cleaned and rebuilt with new seals.
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    • Be sure push rod adjustment between pedal and master cylinder is correct and linkage is not binding.
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    • If the power brake unit has a residual check valve the master cylinder must not have residual check valve.
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    • To test - with the brakes locked up, loosen the brake line at the master cylinder outlet. If this releases the brakes, the trouble is in the master cylinder, push rod adjustment or pedal linkage.
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    • If this does not release the brakes, loosen the hydraulic brake line that goes to the wheel cylinders ( located on the end of the slave cylinder of power brake unit) . If this releases the brakes, the trouble is in the power brake unit, wheel cylinders or brake shoes.
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At Jeff's Bronco Graveyard we have bronco parts for sale, and specialize in Full size Broncos and classic Broncos.