1969 Mach 1 Brakes

I have a 1969 Mach 1 with a rear brake problem.  I have to stand on the brake pedal to make the rear wheels stop.  With the car jacked up and in gear at an idle I have to stand on the brake pedal to make the wheels stop.  Here's what I have done.  I figured the porportioning valve was the problem.  So I took the valve off and sure enought it was frozen up.  I obtained new seals and rebuilt it.  I centered the piston before putting it back on the car.  While I was at it I replaced the old power booster and master cylinder.  I also replaced the rear wheel cylinders, brake shoes, spring kit and drums.  I have front wheel disc on the front that appear to work normal.  I also ran new fluid thru the rear brake lines to make sure it was clean and flowing properly.  I bled the brakes with a vacum bleeder.  I still have to stand on the brake pedal, this is not good.

Anyone have any suggestions?
Mike  

Sounds like a prop val malfunction. Stock proportioning valves are tricky to rebuild so I've read, people getting differing results. If your into show car, concourse find a new or professionally rebuilt one. If you just want it fixed, replace the p val with an adjustable one from Summit. I can't stress enough how good it feels to adjust a balance into your car's front and rear braking. Finding the sweet spot where neither end is locking up, but if they did, 4 tires would be. Adjustability is great.  

how is the pedal...

how is the rear brake adjustment..     i double check with a screw driver through the adjustment hole.. by pushing the star adjuster forward then rearward...   NOT TURNING IT...   if you get more than a 1/8" .. you brakes are out of adjustment..

when you bleed the brakes with a vacuum bleeder.. it doe not recenter the valve properly..



you are going to have to pump bleed the brakes ...

i tend to loosen a bleeder screw... slightly... then.. with the engine off.. with my hand.. tap the brake pedal fast..  just enough to pump some fluid through..   but not enough to pull air back...  it's a skill...  just enough..


is there any chance that the rear brake hose is clogged.. or restricted...    or the brake lines have been smashed by a jack or jack stand..   or they are filled with corrosion..

i also want to make sure that you installed a short shoe and a long shoe on each side.. the short shoe toward the front of the car..    long shoe toward the rear...


i also agree on installing adjustable prop valves to fine tune the brakes if you have changed things..

ford actually changed rear wheel cylinder diameters to adjust brake bias..  

The brake adjustment is ok, and I checked the rear lines before putting the wheel cylinders on by hooking up the vacume bleeder to the line and the fluid flowed good.  So I think the lines are not smashed or blocked.  The shoes are put on correctly.  I really want to keep the original porportioning valve to the keep the car original.  I have two valves one on the car and one in a box.  If when I rebuilt the one on the car and did it correctly (there is not much to this valve)  it may not be in the correct position.  I put it in the center position so the brake lite was off.  The first time I put it on the car, the piston was off center and the brake lite was on, so I opened it up and pushed the valve to the center. I've followed the bleeding sequence that is suppose to center this valve correctly.  I don't know if I'm doing something wrong or what.  The problem with working with this valve is each time the master cylinder has to come off the car to get to the valve and I drip fluid on the paint.  Then I hook it all up again, bleeding ect and when it still dosen't work its frustrating.

I will get the old lady out in the garage today to rebleed the lines again by hand and see what happens.  But I still think its that porp valve.  The last resort will be an aftermarket valve.