Flex Brake Line Replacement

Inspecting, maintaining, and replacing flexible brake lines on a classic car is critical for ensuring safe and reliable braking performance. Over time, these rubber or braided lines can deteriorate, crack, swell, or become internally restricted, potentially leading to brake failure. We join Ross Kiehl and Mark Simpson in the shop to replace the flexible brake line on the rear axle of a 1968 Chevelle SS. In addition, here’s a comprehensive overview of the inspection, maintenance and replacement processes:

Importance of Flexible Brake Lines

- Safety: Flexible lines connect the rigid brake lines to the wheel calipers or drums, allowing for suspension and steering movement. A failure here can result in loss of braking at one or more wheels.
- Age-Related Wear: Classic cars often have original or aged replacement lines that may have deteriorated due to time, heat, and exposure to brake fluid or the elements.
- Performance: Swollen or deteriorated lines can reduce braking efficiency by limiting fluid pressure or causing a spongy brake pedal.

Inspection Process

Perform these checks at least annually or when restoring the braking system:

1. Visual Inspection
- Look for cracks, splits, or fraying in the rubber.
- Check for leaks or fluid residue at connection points.
- Inspect for bulges or swelling when someone presses the brake pedal (a sign of internal breakdown).
- Ensure no abrasion or chafing where lines may contact suspension parts.

2. Feel Test
- Squeeze the line gently—rubber lines should feel firm, not mushy or overly soft.

3. Flex Test
- Turn the wheels lock-to-lock and bounce the suspension to ensure the lines don’t stretch, kink, or rub.

4. Brake Fluid Condition
- Contaminated or dark brake fluid can indicate line deterioration from the inside.

Maintenance Tips

- Flush the brake fluid every 2–3 years to prevent internal corrosion or rubber degradation.
- Use OEM-quality rubber or stainless-steel braided lines as replacements.
- Apply silicone grease on line mounting brackets to reduce wear and rust.
- Regularly inspect line mounting clips to prevent rubbing or vibration damage.

Replacing Flexible Brake Lines

Tools & Materials Needed:
- Line wrenches
- Replacement brake lines (OEM rubber or stainless steel braided)
- Brake fluid
- Brake bleeder kit
- Safety stands and jack

Steps:
1. Lift the Vehicle Securely: Use jack stands and remove the wheels for access.

2. Remove Old Lines: Use a flare nut wrench to prevent rounding off the fittings. Have a container ready to catch brake fluid drips. Disconnect both ends of the line and remove any mounting clips or brackets.

3. Install New Lines: Hand-thread both ends before tightening to avoid cross-threading. Reuse or replace brackets and clips to prevent chafing. Avoid twisting the line—ensure a natural curve with suspension movement.

4. Bleed the Brakes: After installation, bleed the system thoroughly to remove air. Start from the wheel farthest from the master cylinder and work inward.

5. Check for Leaks and Road Test: Press the pedal and inspect all fittings for leaks. Test drive carefully, confirming firm pedal feel and proper braking.

When to Replace

- Every 10–15 years for rubber lines (sooner if cracked or leaking).
- Immediately if any bulging, cracking, or leak is found.
- Consider replacing with stainless braided lines for improved performance and durability—especially if restoring a classic for spirited or show use.

Neglecting flexible brake lines is a common oversight in classic car maintenance. Even if other brake components are in top shape, a single failed hose can render the system ineffective. Regular inspection and timely replacement is a small investment that protects both the car and its occupants.