Problem with 1967 L79 brake system

[Joseph E.]

I've finally bench bled and installed my rebuilt original DC master cylinder and bled the system today. New piston seals and o-rings were installed in each caliper since several had small leaks when the system was taken apart some time ago. New flexible lines were put in. All threaded connections were checked to ensure that they were tight. The brake switch alongside the master cylinder that was removed was reinstalled after the master cylinder was put back in. The line connections were made and the system was bled. The car has manual brakes, not power assisted.My brakes are so soft and spongy that they barely stop the car while moving along my quiet sidestreets. I put the car back up on the jackstands and can find no evidence of leaks at any of the calipers or line connections. I bled the system again but found no air in the fluid. I did, however, notice that the fluid flowed at a much faster rate out of the rear calipers than it does out of the front ones. My "Brake" light on the dashboard does come on when the pedal is depressed with a little bit of force which has never happened since I purchased the car. My understanding is that there is some type of valve in the brake switch that regulates fluid flow. If this valve were stuck, would it cause the problem of soft brakes and restricted flow that I have? There was a suggestion in the archives to "slam" on the brakes to reset the valve in the brake switch which I did but to no avail. Has anyone run into a similar situation or is there something that I'm missing? Thanks in advance for any suggestion or information that would help resolve the problem.Joe 45420

[Edward J.]

Re: Problem with 1967 L79 brake system

Joe, I like to gravity bleed the system, just take the lid off the master and open the bleeders one at a time. and watch the bleeder when opened if theres air in the system you'll see the bubbles from bleeder. done this many times before and its just a one man operation.

[Jim T.]

Re: Problem with 1967 L79 brake system

Joseph from reading your post, you rebuilt the master cylinder and the flow is better out of the rear calipers. Take the cap off and have someone gently push the bake pedal and see if brake fluid is entering the master cylinder reservoir. Be careful and protect painted surfaces from the brake fluid. If the fluid is coming into the reservoir something is not assembled correctly. The switch you refer to only recognizes a pressure difference between the front and rear calipers and illuminates the light to let you know something is wrong.