Master Cylinder Bench Bleeding for Chevrolet Chevy P42 Commercial Chassis 1997

The purpose of bench bleeding is to remove the air from the master cylinder prior to installation. This reduces the amount of bleeding that the hydraulic system will need after the master cylinder is installed on the vehicle.

1. Plug the outlet ports on the master cylinder.
2. Mount the master cylinder in a vise with the front end tilted slightly downward
3. Fill the reservoir with clean brake fluid.
4. Using a tool with a smooth rounded end, stroke the primary piston about 25 mm (1 in.) several times.

As the air is bled from the master cylinder, the primary piston will resist travel and will not allow the full 25 mm (1 in.) stroke.




5. Reposition the master cylinder in the vise with the front end tilted slightly upward.
6. Stroke the primary piston about 25 mm (1 in.) several times.
7. Reposition the master cylinder in the vise so that the master cylinder is level.



8. Loosen one of the plugs.
9. Push the piston into the bore to force the air from the cylinder.

To prevent air from being sucked back into the cylinder, tighten the plug before allowing the piston to return to its original position.

10. Loosen the other plug.
11. Push the piston into the bore to force the air from the cylinder.

To prevent air from being sucked back into the cylinder, tighten the plug before allowing the piston to return to its original position.

12. Fill the reservoir.

Perform normal bleeding procedures after the master cylinder is installed.