Vacuum Brake Booster: Testing and Inspection

Function Test
- Operate brake pedal 10 times with engine stopped. Hold brake pedal down and start engine. System is okay if brake pedal gives. If brake pedal does not give, the defect could be in the check valve, vacuum hose or rubber ring between tandem brake master cylinder and brake booster. Engine's vacuum could be insufficient or filter screen of brake booster is completely clogged with dirt.




Checking Engine Vacuum for Brake Booster
- Disconnect vacuum hose on brake booster.
- Install vacuum tester between brake booster and check valve.
- Check vacuum when decelerating from an engine speed of 3,000 rpm with engine at operating temperature.
- Min value: - 0.35 bar (- 5psi).
- Repeat test several times.
- Minimum value with specified idle speed and engine at operating temperature: - 0.50 bar (- 7 psi).