GM 91174780
Master Cylinder

Begin work on Brake Master Cylinder by taking the reservoir off first. Disconnect both units by removing the Brake Master Cylinder from its booster position. Separate the Piston stopper snap ring first then disconnect the Piston stopper followed by removing the cylinder cup and the plate plate. Take out the primary Piston while protecting the cylinder wall and tap the secondary Piston from its flange onto a wood piece or two soft objects. Separate first the secondary Piston pressure cup and then remove the Piston cup and o-ring from the assembly. Examine every part of the disassembly for signs of trouble then get new components since Piston cups need replacement. First dip all parts in brake fluid and look for wear damage on the master cylinder bore. Replace it if corrosion is severe. Vacate remaining brake fluid from inside the cylinder by running clean fluid through it and then tipping it to drain. Put the o-ring on the master cylinder first and then add new Piston cup parts and secondary Piston and secondary Piston pressure cup components. Place the primary Piston parts including plate and Piston stopper onto the cup. Push and place the Piston stopper snap ring inside the master cylinder chassis. You should reinstall the master cylinder to the brake booster then apply a thin layer of brake fluid on the new grommets before putting them into their proper position on the master cylinder . Finally, reinstall the reservoir.

Remove the reservoir, then disconnect the brake pipes from the master cylinder and from the proportioning valve.