How to Bench Bleed a Master Cylinder in a VW Passat

Written by ehow cars editor
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The VW Passat is an affordable yet luxurious vehicle, available in sedan and wagon styles. If you ever need to replace the brake master cylinder in your Passat, you should make sure to bench bleed the new one before installing it. This eliminates the risk of pushing excess air into your brake lines. You can use these steps for any year VW Passat and it only takes about 10 minutes.

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Things you need

  • Replacement brake master cylinder (varies between model years)
  • Bench bleed kit (may come with the cylinder)
  • Bench vise or clamp-on vise
  • Bottle of DOT 3 brake fluid
  • Phillips screwdriver

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  1. 1

    Remove the old brake master cylinder from your VW Passat. Look for it up toward the firewall, on the driver's side of the engine bay. If you're having trouble finding it, locate the brake fluid reservoir, since it's attached to the top of the cylinder.

  2. 2

    Put your new brake master cylinder in a bench vise or clamp it to an old table to keep it in place. Make sure it's level when you tighten the vise.

  3. 3

    Look for the two fittings that came with your bleed kit and screw them into the outlet holes on the side of the VW Passat's master cylinder. Locate the two pieces of tubing in the kit and insert them snugly into the fittings.

  4. 4

    Bend the tubes up and insert them into the reservoir. Cut them, if you need to, so they sit with the ends about halfway into the reservoir. Clip them to the lip of the reservoir, so they stay put and don't slip; you could end up with air in the system and have to start over if you skip this.

  5. 5

    Pour fresh DOT 3 brake fluid into the reservoir. The hoses will extend down into the fluid, creating a hydraulic system. This means you won't have to clamp the tubes to avoid letting fluid flow back into the master cylinder while you work.

  6. 6

    Insert your screwdriver into the VW Passat's brake master cylinder and push. This moves the piston, forcing brake fluid into the cylinder to clear the air out of it. You'll see brake fluid recycling back into the reservoir.

  7. 7

    Watch for air bubbles coming out of the tubes. If you have clear hoses, you'll see the air bubbles moving through the tubes; if your tubes aren't transparent, watch for bubbles coming out into the fluid in the reservoir. Sometimes bleed kits come with black tubes, so consider buying clear ones if this is the case.

  8. 8

    Keep pumping the piston steadily until you no longer see air bubbles. Leave the hoses in the master cylinder and carefully remove it from the vise: You're ready to install the primed cylinder in your VW Passat.

Tips and warnings

  • You might be able to save money by reusing your old brake fluid reservoir. Many master cylinders come with a new reservoir already installed, but if not, wash out your old one, making sure to dry it off completely, and install it into the new master cylinder.
  • If you get any brake fluid on your VW Passat, immediately wipe it off. Use a towel with soap and water to avoid letting the brake fluid eat through your paint.

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