I changed the rubber brake hoses on my '69 Z28 last night as the existing ones where looking pretty shaby. I added fresh brake fluid to the master cylinder and used a hand held vacuum pump to pull the fresh fluid through. I did the rear drums first and then did the passenger side front disc followed by the drivers front. The tube on the vacuum showed clean fluid with no air bubbles whatsoever. I then bled the brakes with the help from my wife pumping the brakes and holding as i cracked the bleeder. The rears went fine, but when i did the fronts, nothing came out. i checked the m/s resevoir and it was full, but no fluid would come out when i opened the bleeder while she held the brakes firm. I used the vacuum pump again, and with vacuum suction i could get fluid to flow out the caliper with no air, but when i tried to bleed again with brake pressure, no fluid would come out. Could this be that the calipers are frozen, the m/s is bad, or can it have anything to do with the proportioning valve?? thanks for any help.

Do you have peddle pressure???,I didn't ,good peddle press.on the rears ,but then bleed the fronts and lost peddle press. I went through a can of fluid ,before I asked the break shop by my house what's up, he said bad caliper or caliper's (piston hanging up),so I replaced both and Walla great peddle press. And fluid would shoot down the clear bleed hose, not saying this is your prob. But could be ,good luck and Happy Motoring

Does your car have the metering valve on it? It is the roundish looking valve that attaches where the MC bolts to the booster. It "should" allow fluid to pass through it with pedal type bleeding, and "shouldn't" allow fluid through it with pressure/vacuum bleeding. It sounds like your problem is the reverese ofwhat should be happening - wierd.

Crack a brake line at the front reservoir of the MC and have her press the pedal. If fluid comes out there, you can rule out MC. If that goes OK, crack the line coming out of the metering valve and see if you get fluid with pedal pressure.

Kinda work your way down the line until you isolate the problem.

I have had this problem. You need to reset the proportioning valve (distribution/metering block).

great advise, thanks for the input. Will start at the m/s and work my way down. Question - How do you "RESET" the proportioning valve??? Thanks.

great advise, thanks for the input. Will start at the m/s and work my way down. Question - How do you "RESET" the proportioning valve??? Thanks.
Under the rubber boot on the Prop valve is a button to push to reset it. I can only recall that this turns off the brake light but it's been 15 years since I did brakes all day every day.

Jeff

great advise, thanks for the input. Will start at the m/s and work my way down. Question - How do you "RESET" the proportioning valve??? Thanks.

I know of two ways. The first one did not work for me, but is much easier than the second.

Remove the electrical sensing unit and look down into it. You will see a brass shaft in an inner tunnel running horizontal. Try taking a dental tool, pin, or very small flat head screwdiver and slide the brass shaft toward the front, yielding an opening. Replace the sensor and give the bleed process another try.

The second way (which I had to use) is to remove the proportioning valve from the master cylinder. Using and air compressor blow air through all the different orifice, but especially the two front openinngs. My opened up this way and it works great as I type this.

Good Luck!