Power Brake Troubleshooting Help

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(s) 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 line.
  • Soft or weak hydraulic hose (expanding under pressure) – replace hose.
Spongy 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 fluid.
  • Soft or weak hydraulic hose (expanding under pressure) – replace hose.
  • Faulty check valve(s) in master cylinder – repair master cylinder.
Hard Pedal (Excessive pedal pressure needed to stop vehicle – pedal is high and firm on first pump. NOTE: If pedal is pumped once before the hard pedal is received – refer to low pedal section.)
  • 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 check valve
  • Kinked, collapsed, dented or clogged hydraulic lines, hoses or connections – repair or replace faulty part.
  • Swollen master cylinder cups (by fluid contamination) – flush hydraulic 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 connections; ruptured or damaged 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 pistons 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.
Hydrovac Pre-Installation Instructions
      . Rebuild or replace the master cylinder.
      • If you are not replacing the master cylinder, drain and flush the master cylinder and hydraulic line of old fluid.
      • Use hydraulic brake fluid only.
      • Do not use solvent for this operation.
      . Disconnect the vacuum hose.
      • Disconnect the vacuum hose from the engine intake manifold and inspect the hose for collapsed inner wall and check the fitting for carbon build-up. This step insures that the booster receives an adequate supply of vacuum.
      • Replace the hose and clean the fitting and the manifold as needed.
      • Test the vacuum check valve by starting the engine while the manifold vacuum hose is connected to the check valve and the hose to the booster is disconnected.
      • Place the vacuum gauge on the booster side and turn off the engine. The vacuum should remain for 30 seconds.
      • Replace the check valve if it fails this test replace it with our check valve kit or an equivalent.
      • Warranty requests will be refused if gas or oil is present inside the unit.
      • Refer to the "Trouble Shooting Guide" on page 5.
      . Clean the air cleaner.
      • Clean the air cleaner by blowing it out with compressed air or remove it and wash it with solvent.
      • Dry it completely before reinstalling.
      • Inspect the air cleaner hose for deterioration. Replace it if necessary.
      • The air cleaner causes more failures to the booster than any other single factor by letting dirt and water enter the unit.
      . Install the booster.
      • Install the booster and connect all the lines making sure all the fittings are clean.
      • Bleed the hydraulic system using a pressure bleeder.
      • Do not run the engine while bleeding the hydraulic system.
      • TRefer to "Bleeding Procedures" on page 5.
      . Start the engine and check the brakes for proper operation.
Bleeding Procedures - All Vacuum Units

A pressure bleeder is recommended. If one is not available, follow these procedures.
DO NOT run the engine while performing bleeding operations unless specified.

Frame Mounted, 2-Line Units
  • Fill the reservoir of the master cylinder with new heavy duty brake fluid.
  • Frequently check to make certain that the fluid in the master cylinder reservoir maintains at least 1/2 inch of fluid. Failure to do so may require starting over.
  • Pre-bleed the master cylinder by loosening the tube nut and slowly pump the master cylinder until the fluid runs clear. Retighten the nut.
  • Bleed the power unit. Pump the pedal slowly to avoid creating air bubbles in the fluid. The bleeder screws should be opened on the pressure stroke of the master cylinder and closed on the return stroke.
  • Continue the procedure on each wheel until all the bleeder screws run clear without any air bubbles.
  • Refill the master cylinder reservoir and slowly pump the pedal with none of the bleeders open. This allows the master cylinder to evacuate any air bubbles that may remain in the cylinder bore. Air will escape through the compensating port in the bottom of the reservoir.
  • Start the engine and pump the pedal two or three times. Then allow time for the fluid to return to the reservoir. If the pedal is firm but has excessive stroke, adjust the brakes on all the wheels. If the pedal is spongy, it still has air in the hydraulic system. See step 8.
  • Some vehicles may require "surge" bleeding. The engine must be running at idle. Make a firm pedal application. Open and close the wheel cylinder bleeder screws very quickly. Do not let the pedal go clear to the floor. Repeat this step on each wheel. Remember to check the brake fluid level in the reservoir.
  • Proceed with the road test.
Frame Mounted, 3-Line Units
  • Three line units (with the third line connected to the master cylinder reservoir) cannot be properly bled without a pressure bleeder.
  • Set the bleeder pressure at 50 to 60 P.S.I.
  • Be sure the reservoir on the master cylinder is filled above the third line connection port.
  • Do not run the engine during the bleeding procedure.
Firewall Mounted Units
  • Push through boosters, all makes.
  • The bleeding procedure is essentially the same except that the engine should be running at the very beginning and throughout the entire process if a pressure bleeder is not used.
Installation Instructions
Bendix Hydro-boost and Hydromax Delco Hypower and Dual Power

This procedure does not include instruction for bleeding the brake system. The hydro-boost, hydromax, hypower and the hydraulic section of the dual power unit use power steering fluid. The brake system uses hydraulic brake fluid.

  • 1. Fill the power steering pump reservoir with power steering fluid.
  • 2. Start the engine and run it for approximately two seconds. Check the fluid lever and add fluid as required.
  • 3. Repeat step 2 until fluid retains constant level.
  • 4. Raise the front of the vehicle to clear the tires.
  • 5. Run the engine at 1000 to 1500 rpm depressing brake pedal several times.
  • 6. Turn steering right and left lightly contacting the wheel stops.
  • 7. Turn off the engine and recheck the fluid level in the reservoir. Add fluid if needed.
  • 8. Lower vehicle and repeat steps 4 through 7.
  • 9. If the pedal is up and firm, road-test the vehicle.
Power Brake Sales
1517 McCormack Avenue
Sacramento, CA 95811