Owner's Problem Description
The owner has a 1997 Ford Explorer 4WD and has replaced the front brake pads, calipers, rotors, and the master cylinder. Despite these replacements, the brake pedal goes straight to the floor without any resistance. The owner reports that both sides of the brake fluid reservoir are full, and there are no warning lights on the dashboard. There is a noticeable jerk to the right when applying the brakes, and the pedal pushes back against the foot during almost complete stops. Previous to these repairs, no brake issues were noted in the last 60,000 miles.
Professional Technical Analysis
The 1997 Ford Explorer in question is equipped with a 4WD system and has a history of well-maintained brakes until recent repairs. After the owner replaced the front brake calipers, pads, rotors, and the master cylinder, they experienced a complete loss of brake pedal pressure, which goes straight to the floor. This symptom suggests a likely issue with hydraulic pressure loss somewhere in the braking system. The vehicle should be assessed for potential air in the brake lines or a malfunctioning master cylinder despite bench bleeding. Considering the reported jerk to the right during braking, there may also be a caliper issue or a problem with the brake lines themselves. The absence of warning lights could indicate that the ABS is not engaging, but it does not rule out hydraulic failure. The owner has also mentioned that the vehicle was functioning properly before these repairs, indicating that the root cause likely lies within the recent service actions. A thorough inspection of the brake lines for leaks, proper bleeding of the system, and verifying the integrity of the new components is essential. The expected normal brake pedal feel should be firm and responsive, indicating adequate hydraulic pressure throughout the system. Regular specifications for brake system operation include 15-20 PSI of hydraulic pressure at the pedal under normal operation conditions.
Possible Causes
Most common causes (ordered by frequency):
- Air in the Brake Lines: After replacing calipers and master cylinder, it's possible that air has entered the brake lines during the bleeding process. This can lead to a soft brake pedal feel and the pedal going to the floor without any significant resistance. Proper bleeding procedures must be followed, including gravity bleeding both front calipers and ensuring no air bubbles remain in the system. - Soft brake pedal feel, difficulty in achieving solid brake pressure, potential air bubbles during bleeding.
- Master Cylinder Failure: Despite bench bleeding, the master cylinder may still be faulty. If the internal seals are compromised, it can lead to a lack of pressure in the brake system, causing the pedal to sink to the floor. Verifying the integrity of the master cylinder is crucial to ensure it can maintain proper hydraulic pressure. - No resistance in brake pedal, possible internal seal failure, irregular brake fluid flow.
- Caliper or Brake Line Issues: A malfunctioning caliper, such as a stuck piston or a blocked brake line, could also prevent proper brake function. If the calipers are not applying equal pressure, it can cause the vehicle to pull to one side during braking. Inspecting the calipers for proper operation and checking the brake lines for obstructions is essential. - Vehicle pulls to the right while braking, uneven brake pressure distribution.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial Visual Inspection: Start with a thorough visual inspection of the brake system components. Check all caliper connections, brake lines, and fluid levels. Look for any signs of leaks or improper installation that could contribute to the pedal going to the floor.
- STEP 2 - Brake Fluid Bleeding: Perform a proper brake bleeding procedure. Start with the farthest caliper from the master cylinder and work your way toward the nearest. Use gravity bleeding or a vacuum bleeder to ensure all air is removed from the system. Monitor fluid flow and check for any air bubbles.
- STEP 3 - Test Brake Pressure: After bleeding, test the brake pedal feel. The pedal should feel firm and require effort to push down. If it still goes to the floor, further investigation into the master cylinder and caliper operation is required, including checking for any restrictions in the brake lines.
- STEP 4 - Inspect Calipers and Lines: Remove the wheels and inspect the calipers for proper operation. Check for any signs of sticking pistons or damaged seals. Inspect the brake lines for kinks, leaks, or blockages that could affect hydraulic pressure.
