OEM Chevrolet Astro Brake Master Cylinder

Chevrolet Astro Brake Master Cylinder Parts and Q&A

• Master Cylinder
  18047529
  Q: How to bench bleed the brake master cylinder on Chevrolet Astro?

  A:

  To bench bleed Brake Master Cylinder remove the mounting flange and put it inside of a bench vise with the back of the primary Piston. Replace the master cylinder reservoir cap and diaphragm and attach appropriate fittings on the master cylinder ports for the necessary flare seat and hose attachment. Connect transparent hoses to these fittings and run them into the master cylinder reservoir. Add delco supreme ii, gm p/n 12377967 (Canadian P/N 992667), or equivalent dot3 brake fluid to the reservoir at least half full from a clean, sealed container, making sure that the ends of the hoses are completely submerged. Employing a round-ended, smooth tool, press and let go of the primary Piston down to an approximate 25mm (1 inch) several times and view the flow of the fluid from the ports. When air is also bled from the primary and secondary pistons, the effort needed to depress the primary Piston will be greater and the travel will be less. Repeat the same process until free flow of the fluid occurs from the ports without accompanying air bubbles. Then evacuate the removal of the transparent hoses from the reservoir, installing the master cylinder reservoir cap and diaphragm and then removing the fittings with the hoses from the ports, wrapping the master cylinder with a clean shop cloth so that spills can be avoided. Last but not the least, unstuck the master cylinder from the vise.
• Master Cylinder
  18047594
  Q: How should the brake master cylinder be overhauled to ensure proper function and avoid damage on Chevrolet Astro?

  A:

  Brake Master Cylinder overhauls should include new cylinder body replacement instead of bore honing because the hard and polished surface gets damaged when honing occurs which results in premature rubber cup wear. The first step involves removing cover and diaphragm while draining the brake fluid from the reservoir. First disconnect the two locking pins and extract the reservoir assembly and its grommets from the master cylinder body. Use a vise to hold the master cylinder mounting flange while using a bar tool to separate the reservoir from its position. Pull out the snap ring while taking out the primary Piston assembly from the master cylinder body. When extracting the secondary Piston through air pressure place the open cylinder bore end 25 millimeters (1 inch) above a cushioned surface but apply air pressure at a low rate. Apply air pressure to the front port of the master cylinder after plugging the rear port then extract the spring retainer plus the seals and spring. Wash all metal components with denatured alcohol yet rubber components need clean brake fluid for cleaning purposes while checking for any potential contaminants. To check for diaphragm damage examine for cylinder bore scoring or corrosion (cylinder replacement required if corrosion is present) and inspect the reservoir for any sign of cracks. Lubricate the grommets and seals and cylinder bore by using new seals and clean brake fluid during assembly. Install the spring followed by spring retainer before placing the primary seal and secondary seal on the secondary Piston. Position both pistons with the snap ring into the master cylinder body space before fastening it while adjusting the primary Piston when necessary. Screw two fresh grommets onto the master cylinder before putting the reservoir into place then use a rocking motion to set it. To finish the installation you should piece together the reservoir locking pins along with diaphragm placement into the cover to lock the reservoir.