Bleeding the Brakes

I'm upgrading my 54 Pontiac brakes to 4 wheel disk brakes from a 1984 Olds Toronado. I thought that bleeding the brakes would be easy, I've changed master cylinders and calipers before with no problems. Well, that didn't happen this time. I started by using one of the one man job brake bleeder tools which is nothing except a hose and a bottle. I was expecting a one way valve - oh well.

I used it and got unacceptable results and a brake pedal that went to the floor. So I asked my wife to push on the pedal and bled the brake lines again. You bleed the brake lines starting in order with the longest line to the shortest line. Still no improvement and the rear calipers were not adjusting. I figured that it must be a bad master cylinder and purchased a rebuilt unit which was only $10 more than a rebuild kit.

When you bleed the brakes, the first thing that you do is bleed the master cylinder if it has been replaced or the lines disconnected. It can take up to an hour to bench bleed some master cylinders. The rebuild kit that I purchased came with two clear hoses, plastic hose fitting adapters and a clip to hold the hoses in the reservoir
  1. You clamp the master cylinder level in a vice using the mounting tabs and not the master cylinder's body. Screw in the plastic fittings into the brake line ports and route the clear hoses from the plastic fitting back into the front and rear reservoirs. The clip holds the hoses in place in the reservoir.
  2. Next you fill the reservoir with brake fluid and slowly push on the piston. You can see air bubbles through the clear hose. You can lightly tap on the side of the reservoir to dislodge some trapped bubbles also. You'll be surprised at how much air is released by tapping. Then you release the piston. You continue this procedure until there is only brake fluid moving in the clear hoses

I bled the master cylinder according to the instructions and the nice bleeding kit and then my nephew, Ben, helped me bleed the lines again. Same thing, no pressure in the system, it would leak back into the reservoir. My friend Mark came over and he couldn't figure it out also - we concluded that it was another bad master cylinder.

When you manually bleed the brake lines, it normally takes two people. One to push and release the brake pedal and monitor the master cylinder level and the other to open and close the bleeder screws. A 12" piece of clear hose that will fit on the bleeder screw and a clear bottle partially filled with brake fluid is needed.

  1. First, the brake reservoir is filled and the lid is rested on top. If it is clamped down, a vacuum can form and suck the brake fluid back into the reservoir from the brake line
  2. Next, the brake pedal is pushed and held down. Then the longest length brake line (usually the right rear) has its bleeder screw opened (about 3/4 turn). Old brake fluid should come out with lots of air bubbles.
  3. Once there is no more movement of brake fluid through the bleeder screw, it is closed. Then the pedal is released. This sucks brake fluid from the reservoir into the brake lines. This procedure is repeated until there are no bubbles in the line. Then the next caliper is done, the typical sequence is right rear, left rear, right front and left front caliper.

I had this funny feeling that we were doing something wrong. Two master cylinders with the exact same symptons is just too much of a coincidence. I posted a help notice to the newsgroups and found out some things about mid 80s 4 wheel disk brake systems. The front disks are auto-adjusting, the rear are adjusted using the parking brake. The parking brake mechanism "notices" when there is more than 0.030" of play between the pads and the rotor and takes up the slack by "screwing" the piston out.

I installed new pads for the rear (already had new ones in the front) and had to use a special compressor tool that was combination C clamp that turned the piston. What a bitch to do! I had to remove the caliper and disconnect the parking brake cable and brake line. The tool should of been reverse thread as every time I squeezed the piston the tool loosen up. It took 2 hours to change the rear brake pads!

brake tool

Brake tool with 84 Toronado's plate in place

tool set

Brake tool set on loan from local Auto Parts Sources

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Copyright July, 2011 Eugene Blanchard