The fluid level must be maintained at 1/2″ to 1″ below top of master cylinder filler opening at all times. Low fluid level in master cylinder reservoir may permit air to be pumped into the brake pipes and wheel cylinders, necessitating bleeding of the hydraulic system.

Before removing filler cap nut to check fluid level or add fluid, thoroughly clean the cap and surrounding area of cylinder to avoid getting dirt into reservoir. It is recommended that Master Cylinder Filler J 713 and Adapter J 713-2 (fig. 8-5) or a pressure tank be used when filling master cylinder reservoir, to avoid entrance of dirt into the reservoir or the fluid container.

Use only G. M. or Delco Super No.11 hydraulic Brake Fluid. This is an all-weather fluid which will operate satisfactorily in all temperatures and will mix properly when new fluid is added to fluid in the hydraulic system. Do not use reclaimed fluid.

Do not use shock absorber fluid or any other fluid which contains mineral oil. Do not use a container which has been used for mineral oil. Even a trace of mineral oil will cause swelling and distortion of rubber parts in the hydraulic brake system.



A bleeding operation is necessary to remove air whenever it is introduced into the hydraulic brake system. Since air is compressible and hydraulic fluid is not, the pressure of air in the system is indicated by a springy, spongy feeling on the brake pedal accompanied by poor braking action.

Air will be introduced into the hydraulic system if the brake pedal is operated when the fluid is too low in master cylinder reservoir. Air will also enter the system whenever any part of hydraulic system is disconnected.

It will be necessary to bleed the hydraulic system at all four wheel cylinders if air has been introduced through low fluid level or by disconnecting brake pipe at master cylinder. If brake pipe is disconnected at any wheel cylinder, then that wheel cylinder only need be bled. If pipes are disconnected at any fitting located between master cylinder and wheel cylinders, then all wheel cylinders served by the disconnected pipe must be bled. See figure 8-2.

Sequence for Bleeding Wheel Cylinders

It is advisable to bleed one wheel cylinder at a time to avoid getting fluid level in reservoir dangerously low. The correct sequence of bleeding is left front, right front, left rear, right rear. This sequence expels air from the lines and wheel cylinders nearest to the master cylinder first, and eliminates the possibility that air in a line close to the master cylinder may enter a line farther away after it has been bled.

CAUTION: Do not perform bleeding operation while any brake drum is removed.

Bleeding Wheel Cylinder with Master Cylinder Filler J 713

  1. Thoroughly clean master cylinder filler cap nut and surrounding area, then remove cap nut.
  2. Fill Master Cylinder Filler J 713 with specified brake fluid (par. 8-8) and use Adapter J 713-2 to support the filler in place on master cylinder. See figure 8-5.
    1950 Buick Master Cylinder Filler and Adapter

    1950 Buick Master Cylinder Filler and Adapter

    Leave Filler J 713 in place during all bleeding operations as it automatically maintains the proper level in reservoir as fluid is pumped out of master cylinder.

  3. Remove screw and attach Brake Bleeder Tube J 628-A to wheel cylinder bleeder valve. Place lower end of bleeder tube in a clean glass jar. Unscrew bleeder valve 3,4. of a turn, using Bleeder Wrench J 627. See figure 8-6.