Metal lines and rubber brake hoses should be checked frequently for leaks and external damage. Metal lines are particularly prone to crushing and kinking under the vehicle. Any such deformation can restrict the proper flow of fluid and therefore impair braking at the wheels. The flexible rubber hoses should be checked for cracking or scraping; such damage can create a weak spot in the hose and it could fail under pressure. The flexible rubber hoses are also susceptible to collapsing internally causing a restriction in the fluid flow. If when bleeding the brakes, the fluid flow seems restricted or excessive pedal pressure is needed to depress the brake pedal, the fluid line may be internally restricted.
Any time the lines are removed or disconnected, extreme cleanliness must be observed. Clean all joints and connections before disassembly (use a stiff bristle brush and clean brake fluid); be sure to plug the lines and ports as soon as they are opened. New lines and hoses should be flushed clean with brake fluid before installation to remove any contamination.
A brake pedal with a spongy feel can be caused by fatigued flexible rubber hoses, which under pressure expand. This can sometimes be felt by having an assistant press and release the brake pedal while squeezing the flexible line by hand and feeling for the line to swell when the brake is applied.
For off road closed course use many enthusiasts replace the rubber flexible lines with braided steel flexible brake lines. This typically improves the brake pedal feel and lessens the chance of a spongy pedal, however there may be restrictions and other concerns that must be addressed for general street use. Before replacing the flexible brake lines on your vehicle, consult the laws concerning state Inspection, and the brake line manufacturer for their recommendations.
When removing or installing the brake pipes, line or hoses, always use a backup wrench on the fitting to prevent twisting. Avoid bending the lines or damaging the coating. Use a tubing bender if the line needs to be bent. Use pre-made lines with the flare already constructed. Torque for most of the compression fittings is 11 ft. lbs. (15 Nm).
- Disconnect the negative battery cable.
- Raise and safely support the vehicle on jackstands.
- Remove any wheel and tire assemblies necessary for access to the particular line you are removing.
- Thoroughly clean the surrounding area at the joints to be disconnected with brake cleaner.
- Place a suitable catch pan under the joint to be disconnected.
- Using 2 line wrenches, if available, (one to hold the joint and one to turn the fitting), disconnect the hose or line to be replaced. If at first the metal line begins to turn with the flare nut, spray the area with a rust penetrating lubricant and allow to soak in. Slowly loosen and tighten the flare nut until the metal line breaks loose from the flare nut. If necessary, hold the metal line with a very small pair of gooseneck pliers, but Do NOT crimp or crease the line. Move the flare wrench back and forth in small movements until the flare nut can move without twisting the metal line.
- Disconnect the other end of the line or hose, and move the drain pan, if necessary. Always use a back-up wrench to avoid damaging the fitting.
- Disconnect any retaining clips or brackets holding the line and remove the line from the vehicle.
- Install the new line or hose, starting with the end farthest from the master cylinder. Connect the other end, and then confirm that both fittings are correctly threaded and turn smoothly using finger pressure. Make sure the new line will not rub against any other part. Brake lines must be at least 1/2 in. (13mm) from the steering column and other moving parts. Any protective shielding or insulators must be reinstalled in the original location.
- Using 2 wrenches as before, tighten each fitting.
- Install any retaining clips or brackets on the lines.
- If removed, install the wheel and tire assemblies, then carefully lower the vehicle to the ground.
- Refill the brake master cylinder reservoir with clean, fresh approved brake fluid, meeting DOT 4 specifications and bleed the brake system as outlined in this section.
- Connect the negative battery cable.