How to Bleed a GM Master Cylinder


As you depress the brake pedal, the master cylinder on your GM model forces brake fluid and develops pressure in the brake lines and hoses to help you slow or stop the vehicle. But wear and parts failure may cause the pistons to leak or the valves to fail. In this case, it is necessary to install a rebuilt or new brake master cylinder. However, before you do that, follow this guide to bench bleed the cylinder before installing it.

Things You'll Need

  • Vise
  • Vise caps
  • Bleeding or clear silicone tubes
  • New brake fluid DOT 3
  • Phillips screwdriver
  • Mount the brake master cylinder in a vise and use vise caps to prevent damage to the master cylinder.

  • Detach the cap from the cylinder reservoir.

  • Install bleeding or clear silicone tubes of the proper length on the brake line fittings of the cylinder. Then bend the tubes over and into the reservoir. Most manufacturers deliver new or rebuilt master cylinders with bleeding tubes included in the package.

  • Fill the cylinder reservoir with new brake fluid DOT 3 up to a quarter inch of the reservoir's top. Check that the ends of the bleeding or silicone tubes are submerged into the brake fluid, or air will be reintroduced into the cylinder assembly.

  • Depress the piston all the way into the bore slowly and then let go. Use a Phillips screwdriver. Keep depressing the piston until you see no more air bubbles going through the bleeding or silicone tubes.

  • Remove the ends of the bleeding tubes from the cylinder reservoir.

  • Add more brake fluid to the master cylinder reservoir to bring the fluid to the previous level.

  • Install the brake master cylinder on your GM vehicle following the instructions in your vehicle's service manual.

  • Remove one bleeding or silicone tube at a time as you connect the brake lines to the cylinder line fittings.

  • Bleed the wheel cylinders and brake calipers following the bleeding sequence indicated by your car manufacturer. If necessary, consult your vehicle's service manual.

Tips & Warnings

  • As you may have noticed, the new or rebuilt brake master cylinder for your GM model came without fluid. You should bench bleed the cylinder before installing it to avoid damage to the pistons inside the assembly.

Related Searches


  • Chevrolet Silverado GMC Sierra 1999 thru 2006 Haynes Repair Manual; Jeff Kibler and John H Haynes; 2008
  • Modern Automotive Technology; James E. Duffy; 2003
  • Photo Credit Bull-Doser/, Ryan Frost/
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