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Power Brake Unit

  1. Inspect vacuum hoses between power brake booster and check valve, and between engine and check valve for cuts, abrasions, cracking or other obvious damage. replace if necessary. Blow into both ends of check valve. Ensure air flows in one direction only (toward engine). If not, replace check valve.
  2. Disconnect vacuum hoses from check valve. Remove check valve. Using Rotunda Tester (014-R1058), apply 19.69 In. Hg vacuum to both sides of check valve. Vacuum should exist on booster side of check valve and should not exist on engine side.
  3. Check hydraulic brake system for leaks or low fluid. With transaxle in Park or Neutral, stop engine and apply parking brake. Depress service brake pedal several times to exhaust all vacuum in system.
  4. With engine off and all vacuum exhausted, depress brake pedal and hold it in applied position. Start engine. If vacuum system is operating, pedal will tend to move downward under constant foot pressure. If motion is not felt, vacuum booster system is not functioning.
  5. Remove vacuum hose from power brake booster. Manifold vacuum should be available at booster end of hose with engine at idle and transaxle in Neutral. Ensure all unused vacuum outlets are sealed and all vacuum hoses are in good condition.
  6. After ensuring manifold vacuum is available to power brake booster, connect vacuum hose to booster and repeat steps  3 and  4 . If no downward movement of pedal is felt, replace power brake booster.
  7. Operate engine a minimum of 10 seconds at a fast idle. Stop engine and let vehicle stand for 10 minutes. Depress brake pedal with 20 lbs. (9 kg) force. Pedal should feel the same as with engine operating. If pedal feels hard (no power assist) inspect and test check valve. See steps  1 and  2 .
  8. If necessary, replace check valve and repeat previous step. If pedal still feels hard, replace power brake booster. If brake movement feels spongy, bleed hydraulic system. See BLEEDING PROCEDURE  under BLEEDING BRAKE SYSTEM.
  9. Run engine at fast idle for 10 seconds or longer. Depress brake pedal and listen for noise. Compare results with a known good system. If power brake booster is noisy, replace booster.
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