Hi all, new member here. I have a problem that I am hoping someone can help me with. I have a 79 1/2 ton 4x4, with brake issues. I have replace master cylinder. vacuum booster, pads, shoes. Still no brakes. Feels like air in the lines but I have bled the **** out of them. I also bench bled the master cylinder. There is pedal with the truck off but once you start the truck I lose all pressure. My vacum hose and check valve are good. brake lines are all good - no kinks that I can find. Wondering if I am not getting enough vacuum to create the pressure when the truck is running? The vacuum line runs into the carb. Not sure if there is a way to test the vacuum pressure? I believe that it should be about 18lbs? When bleeding the lines in the front there is no pressure, once I open the bleeder screw there is a pause before fuild shoots out. Any help would be great. Thanks in advance.

Don

 

Dear Weezee

As you said, you have replaced all parts that is Master Cylider, Booster, pads and may be lines but getting same problem.

I feel you are sure 100 percent every part is functioning properly, it seems that brake fluid is moistured.

Because brake oil absorbs moisture quickly as you open reservior cap for few minutes or their is any permaneny open leak their that absorbs moisture. OR may be your fluid is older.
Its better to flush brake oil completely and then refill and bleed again.
Please note, a little air buble can lead to completely depressed brake padel.
Make sure there is no buble inside lines.

I hope you problem will be solved if carefully bleeded. Normally bleeding requires 1 more person to pump the pedal.

Please feel free to contact me

mycolleagues@yahoo.com
Babar from Pakistan

 

Had a similar problem with my 86 pickup.
It turned out to be the rubber flex hoses. They become soft internally and will actually swell causing a lag in pressure.