I have been struggling through a problem with my brake pedal going to the floor on my '70 wagon, (power disc/drum). Master cylinder is good, and has been bench bled. The front brake lines have been replaced and the system has been bled. I can't find any visible leaks.

When bleeding the rear brakes, only a small squirt of fluid comes out when my son presses the pedal down. Also, when I pulled one of the drums, I noticed that the brake shoes are not even moving when the pedal is pressed.

Could my proportioning or metering valve be failing to send enough pressure to the rear? Any suggestions on what you think my problem is and how to fix it? Thanks in advance, Steve

That's the exact problem i have! I haven't figured it out yet though! Good Luck!

SS, I am having the same problem with my 70 Malibu. I just installed a brand new Hydroboost system and ran into trouble trying to bleed the brakes. I bench bled the M/C and it is fine. Got no fluid from the either rear brakes but the fronts are fine. I called the guy from Hydroboost and he suggested the combination valve has tripped so that no fluid is going to the rear. He gave me a couple of suggestions to open it up. But they didn't work. Here is what he told me to try - 1) Pump up the brake pedal a few times and then hold it to the floor. While the pedal is on the floor, have a helper crack open the left front bleeder screw. The system should detect a drop in pressure and the allow the comb valve to open to compensate. 2) Remove the brake fluid line from the m/c front reservoir and install a plug in it. Pump up the brake pedal and you should then hear the comb valve click open allowing fluid to go to the rear. Neither of these worked for me so I pulled the comb. valve and sprayed it real good with BrakeKlean. I then ran some compressed air through the input ports and felt that air was coming out the output ports. I plan to re-install the comb. valve, in a day or two, see if if things are better.

SS Wagon ,did you find the problem ? You may try gravity bleeding the rears to get the fluid flowing back their, keep us posted.

The metering valve isn't the problem...it's operates in the front system only.

On my '69 I had a bunch of trouble trying to bleed my rear brakes after installing my Hydroboost, too. But the Hydroboost wasn't the problem. I tried replacing the M/C, but that didn't do any good. I was looking at replacing the distribution block, too, but decided that wasn't the problem since the "BRAKE" idiot light wasn't constantly lit--it was only lighting when trying to bleed. So I decided the line going to the rear must be clogged. And damned if that wasn't it. I cut the rear flex hose in half and found it plugged solid. I ended up replacing that rear flex hose and the entire long line from the distribution block back to the flex, both rear axle lines, and the rear brake cylinders. After that, brake fluid just gushed out of those bleeders.

There was 35 years worth of brake crud in the rear brake system and I wouldn't be suprised if you've got the same problem.

I could never get good pedal following my restoration rebuild. I had to MityVac the fluid to the rear to get a good bleed. I started with all new parts and a completely dry system though. I also used silicone fluid which is a little harder to bleed (it's slightly thicker).

I'd agree that your lines may be clogged. A weak rubber hydraulic hose can do the same thing, it expands instead of passing the hydraulic pressure to the wheel cylinders/calipers.

OK, great suggestions guys!! I replaced the rear wheel cylinders this weekend thinking that if they were frozen the rear shoes would not move. Still no movement of the shoes. I will move to the rear brake lines next. Thanks again for the input.

disconnect the hard line from the flex hose at the rear end, press pedal and if fluid comes out, problem is rear lines and hose. no fluid, disconnect at proportioning valve and try again, no fluid, check valve. This way you can isolate problem area and fix. Also, whenever I replace a wheel cylinder or caliper, I fill it with fluid on the bench, then install, that way there is less to have to fill from the master to get a good bleed.

As Rich stated even with a new system and lines he had problems getting fluid to flow to the rears, Try gravity bleeding the rears see if you can get some volume of fluid flowing from those bleeders, I just went though this with my 68 after a mc replacement, also you may try adjusting the rear shoes very tight to limit travel of the wheel cylinders, just remember to back them off when system is bled. If all else fails try pressure bleeding them, do a search on "brake bleeding" someone made a unit out of a garden spayer for about 20 bucks, Keep us posted