Brakes Go to Floor After Replacing Master Cylind (1995 Honda Civic LX)
This article addresses a critical braking issue encountered on a 1995 Honda Civic LX. The car exhibits erratic brake performance, with complete failure occurring in some instances. This poses a serious safety hazard and requires immediate attention.pen_spark
Problem Overview: Inconsistent Braking in a 1995 Honda Civic LX
Let’s assume the braking behavior as follows:
- Inconsistent performance: Brakes function perfectly 50% of the time, but fail entirely 5% of the time.
- Speed dependence: Failure becomes more likely at lower speeds (around 5 mph) and on slight inclines.
- Pedal travel: The brake pedal occasionally goes to the floor before any braking effect is felt.
- Emergency brake: The parking brake functions normally.
Symptoms and Initial Observations
Based on the above information1995 Honda Civic LX where the braking performance is alarmingly inconsistent. Specifically, while the brakes function normally about 50% of the time, there are occasions when they fail entirely, particularly at lower speeds and when on slight forward slopes.
This inconsistency poses a significant safety risk, especially since the vehicle’s brakes are more likely to fail when moving slowly or exiting parking lots.
Troubleshooting Performed
You have undertaken significant efforts to rectify the issue, including:
- Bleeding the brake system on multiple occasions (3 and 4 wheels)
- Replacing a wheel cylinder
- Replacing a brake caliper
- Replacing the master cylinder
- Flushing the entire brake system
- Verification of no leaks in the brake lines
Despite these actions, the problem persists.
Diagnostic Steps Taken
To address the issue, you’ve undertaken several maintenance actions, including bleeding the brakes multiple times and replacing critical components such as a wheel cylinder, a caliper, and the master cylinder. You also completely flushed the brake system.
Despite these efforts, the problem persists: the brake pedal occasionally goes to the floor without resistance, indicating a failure in the braking system’s ability to generate adequate hydraulic pressure.
Causes of Brake Inconsistency
Based on the above information, several potential causes can be identified:
- Incomplete bleeding: Air trapped within the brake lines can cause a spongy pedal and reduced braking effectiveness. While bleeding has been performed, there might still be air in the system, particularly in the master cylinder.
- Faulty master cylinder: Even a new master cylinder can be defective. A malfunctioning internal seal can lead to inconsistent brake pressure and pedal travel.
- Proportioning valve malfunction: This valve regulates pressure distribution between the front and rear brakes. A sticking valve could explain the bias towards rear brakes observed during partial brake engagement.
Air in the Hydraulic System
The most common cause of brake pedal inconsistency, particularly the sensation of the pedal sinking to the floor, is air trapped within the hydraulic brake lines. Even small amounts of air can significantly impair the system’s ability to transmit force effectively.
Potential Master Cylinder Damage
Your description suggests that the replacement master cylinder might have been damaged during installation. If the brake pedal is depressed fully to the floor during bleeding, it can damage the internal seals of the master cylinder, replicating the symptoms of the original faulty part.
Proportioning Valve Issues
Given the vehicle’s age and your description of the rear brakes engaging disproportionately, it’s plausible that the proportioning valve, which regulates the pressure between front and rear brakes, is malfunctioning.
This valve ensures that the rear brakes do not engage too quickly, preventing rear wheel lockup before the front brakes have applied sufficient force.
Detailed Solution to Brake Problems
Comprehensive Bleeding Technique
- Bench Bleeding the Master Cylinder: Before reinstalling it into the vehicle, ensure that the master cylinder is bench bled to remove any trapped air. This can be done by disconnecting the brake lines, connecting them back into the master cylinder outlets, and then pumping the brake pedal until no more air bubbles emerge from the fluid.
- Systematic Bleeding of Each Wheel: Begin with the wheel farthest from the master cylinder (usually the right rear), then proceed to the left rear, right front, and left front. This method helps ensure that all air is purged from the lines.
Adjusting Rear Drums
Rear drum brakes require regular adjustment to maintain effective braking force. If the drums are not adjusted to have a slight drag, they can cause the brake pedal to feel soft or unresponsive as the shoes have to travel too far to contact the drum.
Re-evaluating the Master Cylinder and Proportioning Valve
- Test for Internal Leaks: If bleeding and adjusting do not resolve the issue, consider the possibility of an internal bypass in the master cylinder. Observing the behavior under pressure (by having someone press the brake pedal while you check for fluid leakage or listen for air escaping at the master cylinder) can help diagnose this.
- Inspecting the Proportioning Valve: Given the age of your vehicle and the symptoms described, the proportioning valve may be faulty or stuck. If the valve is suspected to be the culprit, replacing it or having it professionally inspected could resolve the uneven braking force distribution.
Preventing Future Damage During Maintenance
To avoid damaging the master cylinder during bleeding, place a block of wood under the brake pedal to prevent it from being fully depressed. This precaution protects the internal seals from being overstressed and maintains the integrity of the hydraulic system.
By following these steps and carefully monitoring each component’s functionality, you should be able to restore consistent, reliable braking performance to your 1995 Honda Civic LX.
Warning
It’s important to emphasize that brakes are a safety-critical system. If you lack the confidence or expertise to perform these repairs yourself, consult a qualified mechanic to diagnose and fix the problem. Never compromise on your safety when it comes to your vehicle’s brakes.
Final Thoughts
In conclusion, achieving consistent and reliable braking performance on your 1995 Honda Civic LX requires a methodical approach. By following the outlined steps, addressing potential air pockets, faulty components, and proper bleeding techniques, you can ensure safe and predictable braking. If the issue remains unresolved, seek assistance from a qualified mechanic to guarantee your car operates at its full safety potential.