BMW Cars 1999-06

Brake Hoses & Lines

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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.


NOTE
For liability reasons, it is suggested that if a flexible brake line must be replaced, replace the brake line(s) with an original equipment BMW replacement part.



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Fig. View of an open end wrench beside a flare nut wrench. To prevent rounding off a flare nut, use a flare nut wrench when loosening hydraulic lines



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Fig. Metal brake lines are attached to flexible lines and the junction supported by a bracket. Flexible lines are used where movement is necessary



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Fig. The flexible hose for the clutch slave cylinder is crimped onto a fitting with a metal line and flare nut

Removal & Installation




NOTE
If the vehicle is equipped with ASC+T, the BMW Service Tester must be used to properly bleed the system. Due to safety and liability issues, this job should only be performed by a BMW dealer.

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 all fittings to 10 ft. lbs. (14.2 Nm).

  1. Disconnect the negative battery cable.
  2.  
  3. Raise and safely support the vehicle on jackstands.
  4.  
  5. Remove any wheel and tire assemblies necessary for access to the particular line you are removing.
  6.  
  7. Thoroughly clean the surrounding area at the joints to be disconnected with brake cleaner.
  8.  
  9. Place a suitable catch pan under the joint to be disconnected.
  10.  
  11. Using two 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.
  12.  
  13. Disconnect the other end of the line or hose, moving the drain pan if necessary. Always use a back-up wrench to avoid damaging the fitting.
  14.  
  15. Disconnect any retaining clips or brackets holding the line and remove the line from the vehicle.
  16.  


NOTE
If the brake system is to remain open for more time than it takes to swap lines, tape or plug each remaining clip and port to keep contaminants out and fluid in.



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Fig. Use a brush to clean the fittings of any debris



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Fig. Use two wrenches to loosen the fitting. If available, use flare nut type wrenches



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Fig. Any gaskets/crush washers should be replaced with new ones during installation



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Fig. Tape or plug the line to prevent contamination

To install:

  1. Install the new line or hose, starting with the end farthest from the master cylinder. Connect the other end, 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.
  2.  


WARNING
Make sure the hose is NOT kinked or touching any part of the frame or suspension after installation. These conditions may cause the hose to fail prematurely. If bending is necessary, use a round wooden dowel or a sealed metal aerosol container to form the line as necessary.

  1. Using two wrenches as before, tighten each fitting.
  2.  
  3. Install any retaining clips or brackets on the lines.
  4.  
  5. If removed, install the wheel and tire assemblies, then carefully lower the vehicle to the ground.
  6.  
  7. 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.
  8.  
  9. Connect the negative battery cable.
  10.  

 
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