1997 F-150 Brake Booster Troubleshooting

Ford trucks have long been valued for their rugged reliability.

Power brakes are standard equipment on 1997 F-150s, even in the base trim models. The power in braking is provided by the brake booster. The brake power booster on the truck is vacuum-actuated, like the vast majority of power brake-equipped vehicles of recent times. When the brake pedal is depressed, a valve inside the booster opens to create a pressure differential across the large circular diaphragm that assists pedal efforts. Troubleshooting booster problems can be accomplished with no tools or expertise of the matter, but repairs may require more strenuous undertakings.

Things You'll Need

• Assistant
• Flashlight Vacuum gauge

Instructions

1. Remove the plastic vacuum fitting, or check valve, from the booster grommet. Twist the valve slightly to ease extraction from the grommet and then from the supply hose. Replace the valve if cracks appear in the plastic valve body. Adapt the vacuum gauge to fit the booster supply hose, and start the engine. Monitor the gauge needle for a steady reading near 20 inches of mercury. Check for clogs in the hose or engine supply nipple if readings are lower than 17 inHg at sea level. Readings at higher elevations will be proportionally lower.

2. Turn the engine off and use the flashlight to inspect the interior of the booster. Replace the brake master cylinder if brake fluid is present in the cavity, as this indicates seal failure of the master cylinder. Replace the booster in this instance also, as the contamination can lead to diaphragm failure. Fully insert the plastic check valve into the booster supply line and grommet if no contamination is noted.

3. Start the engine and wait for the idle speed to stabilize. Listen intently under the hood to locate any loud hissing that indicates a substantial vacuum leak. Repair or replace engine vacuum hoses that leak noticeably, as they may affect engine performance and booster function. Inspect the booster supply hose for leaks, kinks or collapsed areas. Replace any weakened hose with original equipment-compatible parts.

4. Stand in the front of the truck, near the booster. Close the driver's door and have an assistant depress the brake pedal, as though at a red light. Maintain even pressure on the brake pedal while listening to the booster. Replace the booster if hissing sounds continue for more than two to three seconds after initial pedal application. Constant hissing from the booster with even pedal pressure indicates a defective booster diaphragm.

Tips & Warnings

• You may need a step stool to get near enough to test or inspect certain components, because of the high ride height of the F-150. Fashion a stethoscope from a small funnel and some tubing to help pinpoint vacuum leaks. Light hissing heard in the interior of the truck cab when the brake pedal is depressed is considered normal by factory standards.

• Stay well clear of moving parts when working around a running engine.

References

• Edmunds: 1997 Ford F-150 Features & Specs
• Automotive Suspensions Steering Alignment and Brakes; Walter E. Billiet and Walter Alley