Inspection and replacement of brake lines and hoses of the hydraulic brake system (BMW 5 Series E28)

Brake fluid is poisonous. It is also a strong paint solvent. See Warning at the beginning of Section Bleeding the hydraulic brake system.

Inspection

At certain intervals of time specified in Table of sizes and adjustment data at the end of the Manual, you should inspect the brake lines and hoses. With the vehicle jacked up and securely supported on axle supports, inspect the flexible hoses for cracks, wear on the outer casing, fluid leaks, abrasions, and other damage. Hoses are an important and vulnerable part of the braking system, so the inspection must be very thorough. Metal tubes should be inspected for deep cavities and corrosion. If a hose or tube shows any of the above defects, replace it.

To thoroughly inspect hoses and tubes, it is useful to use a flashlight and a mirror.

Replacing flexible hoses

1. Clean all dirt from the ends of the hose. Have a suitable container ready to collect any liquid that splashes when disconnecting the hose.



2. To disconnect the hose from the chassis side, loosen the nut on the metal brake pipe while holding the hex fitting on the end of the flexible hose (lower right arrow) using a split open-end (brake) wrench (top right arrow). If the nut is stubborn, soak it in oil. After disconnecting the hose from the line, remove the spring clamp (left arrow) from the bracket and then disconnect the hose from the bracket.



3. To disconnect the flexible hose from the caliper, simply loosen the mounting screws. If the hose is going to be disconnected for a while, plug the nipples on the caliper to prevent dirt from getting in.

4. Reinstall in reverse order. Make sure the brackets are not damaged and the lock nuts are securely tightened. If the spring clamps are loose, replace them.

5. Check again carefully to make sure that no suspension or steering components are in contact with the hoses. Have an assistant turn the steering wheel from lock to lock while checking.

6. Bleed the brake system as described in Section Bleeding the hydraulic brake system.

Replacing metal brake lines

When replacing brake lines, use only genuine parts - preferably from a BMW dealer.

Genuine BMW brake lines are supplied directly. To give them the desired shape, you will need a tube bender.

1. First remove the tube you are going to replace, place it on a clean workbench and measure it carefully. Prepare a new tube of the same size and bend it to the shape of the old one.

Do not bend or damage the line. The bending radius should never be less than 14 mm. Make sure that the protective coating on the new line is not damaged at the bends.

2. When installing a new brake line, make sure it is properly supported by brackets, that its route is the same as the original, and that it is well clear of moving or hot components.

3. After installation, check the brake fluid level in the master cylinder and add fluid if necessary. Bleed the brake system as described in Section Bleeding the hydraulic brake system and check the brakes before operating the vehicle. Make sure there are no fluid leaks.

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