VW Passat & Audi A4 1990-2000

Bleeding The Brake System

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The following procedure is for models not equipped with Anti-lock Braking Systems (ABS).


NOTE
The brake fluid should be replaced at least every 2 years as it is hygroscopic and absorbs moisture from the ambient air. Always keep brake fluid in a sealed container. Only use a brake fluid that meets the US standard FMVSS 116 DOT 4.


WARNING
Brake fluid is poisonous and corrosive. Avoid spilling brake fluid on the vehicle's paint. It will damage the finish. If a spill does occur, wash it immediately with water.

The purpose of bleeding the brakes is to expel air trapped in the hydraulic system. The system should be checked for fluid condition, brake hose condition and air whenever the pedal feels spongy. The system must be bled whenever it has been opened, repaired, or a hydraulic component replaced. If you are not using a pressure bleeder, you will need an assistant for this job.


WARNING
NEVER reuse brake fluid that has been bled from the brake system. Brake fluid absorbs moisture that can lower its boiling point, therefore re-using old, used, or contaminated fluid can decrease the effectiveness of the braking system.

BLEEDING

When bleeding the brakes, air may be trapped in the brake lines or valves far upstream, as much as 10 feet from the bleeder screw. Therefore, it is very important to have a fast flow of a large volume of brake fluid when bleeding the brakes, to make sure all of the air is expelled from the system.


NOTE
Proper manual bleeding of the hydraulic brake system will require the use of an assistant unless a suitable self-bleeding tool is available. If using a self-bleeding tool, refer to the manufacturer's directions for tool use and follow the proper bleeding sequence listed in this section.


WARNING
Avoid spilling brake fluid on the vehicle's paint. It will damage the finish. If a spill does occur, flush it with water immediately.


NOTE
If the master cylinder reservoir runs dry during the bleeding process, restart from the first fitting.

To bleed the brakes, proceed as follows.

  1. Remove the old brake fluid from the reservoir using a siphon gun or a baster and clean the brake master cylinder reservoir with a clean lint-free cloth. If necessary, remove the reservoir and flush out with brake cleaner.
  2.  


WARNING
When bleeding the brakes, the reservoir must be free of all debris and contaminated fluid, otherwise there is a risk that the master cylinder check valve will become contaminated and fail to function properly, requiring replacement of the master cylinder.

  1. Bleed the brake system at each fitting. Do NOT proceed to the next fitting until all air bubbles are removed from the previous fitting. Bleed the brakes, making sure to following this sequence:
  2.  
  3. 1-Right Rear
  4.  
  5. 2-Left Rear
  6.  
  7. 3-Right Front
  8.  
  9. 4-Left Front
  10.  


NOTE
If the vehicle is equipped with a rear pressure regulator, move the regulator lever when bleeding the rear brakes.

  1. Attach a clear plastic hose to the bleeder screw, then place the hose into a clean jar that has enough fresh brake fluid to submerge the end of the hose.
  2.  
  3. Have an assistant pump the brake pedal ins a smooth, easy fashion, 3-4 times, and hold it down keeping pressure on it, then open the bleeder screw at least 1 / 4 turn. When the bleeder screw opens, the brake pedal may drop further and should be kept pressed down. Have the assistant hold it there until the bleed valve is closed.
  4.  
  5. Close the bleeder valve and have the assistant slowly release the brake pedal only AFTER the bleeder valve is closed, then check the master cylinder fluid level and top off as necessary.
  6.  
  7. Repeat the bleeding procedure until all there are no air bubbles, or a minimum of 4 or 5 times at each bleeder screw, then check the pedal for travel and feel. If the pedal travel is excessive, or feels spongy, it's possible enough fluid has not passed through the system to expel all of the trapped air.
  8.  


NOTE
Constantly check and top off the master cylinder. Do NOT allow the master cylinder to run dry, otherwise air will re-enter the brake system.

  1. Once completed, pump and check the brake pedal for a firm feel, then, if the pedal pressure is firm, test drive the vehicle to be sure the brakes are operating correctly and that the pedal feel is firm during braking.
  2.  


NOTE
If the brake pedal has good pedal pressure after bleeding, but later requires being pumped up to regain pedal pressure, check the system for fluid leaks. If no fluid leaks are present, the master cylinder has most likely failed.



Click image to see an enlarged view

Fig. A one man bleeder unit such as this one, can be purchased at you local aftermarket parts supplier



Click image to see an enlarged view

Fig. Check the fluid level often, and top off the master cylinder reservoir as necessary as the system is being bled

 
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