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Problem: Ineffective bench bleeding causing air to enter hydraulic system

Cause: Air left in the no-pressure areas of master cylinder (Sections A & C in Figure 81.1) migrates to pressure areas once master cylinder is installed.

screen-shot-2016-10-17-at-9-59-17-am Figure 81.1

Solution: Apply unconventional bench bleeding technique to insure all air is removed during bench bleed process. Most master cylinders can be bench bled using either vacuum or pressure bleeding techniques. For vacuum bench bleeding see the next Tech-Tricks Tuesday article next week. Here are the steps to pressure bench bleed a master cylinder:

1. Mount the master cylinder in a vise with the outlets at the highest point.

2. Fill the master to a normal level with clean, new brake fluid.

3. Install the cap adapter making sure there is a good fit.

4. Depress the master cylinder piston about 1/8″ and hold it there using a pair of needle nose vise grips (See Figure 81.2). Make sure to grip against the snap ring and not the cylinder bore. This step changes the fluid path.

screen-shot-2016-10-17-at-10-03-58-am Figure 81.2

5. Install bench bleeding kit or brake lines at master cylinder outlets. Connect hoses and run them into a capture container.

6. Apply pressure to the reservoir. The air and fluid will be discharged into the capture container (See Figure 81.3). Allow fluid to flow until no air is seen in the outlet lines.

screen-shot-2016-10-17-at-10-05-25-am Figure 81.3

NOTE: Phoenix Systems suggests for the easiest bench bleed possible, to conduct the process with the V12 Bench Bleeder Kit. The Phoenix Systems V12 Bench Bleeder kit is a time saving tool that comes with all the parts necessary for the most effective bleeding possible. Follow the link below to see how you can use this product in your own home and automotive service shops.

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