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Problem bleeding brakes...Proportionng valve question...

48K views 16 replies 10 participants last post by  JJLT1 
#1 ·
This is all on my 72 Elky...I replaced my master cylinder as I was having trouble with my brakes. I would have a very spongy pedal and it would keep reoccuring and the MC was original so I figured it was worth replacing anyways. Bench bled it before installing. Went to bleed the brakes, and the brakes won't bleed. Bought a vacuum bleeder kit and was pulling 25lbs of vacuum at the rear and still nothing.

Now here is my question. I took a look at the proportioning valve and noticed that the little plunger under the rubber boot is stuck in. I have no idea what this plunger does, if it is supposed to be like that (which I assume it should be up), and if it could be causing the problems bleeding the rear brakes. I thought about replacing it just because but another $70 for that part I figured I'd ask before wasting the time and $$$. The fronts do bleed, although not that well and should be stronger. Any ideas before I go spend $$$ and let the shop fix it? I really appreciate any help!
 
#4 ·
I just replaced the master cylinder on my 72. The GM factory service manual says ro open the valve on the proportiong vave using tool J-23709 when bleeding the brakes on cars having front wheel caliper brakes. Is ther another way to do this without that special tool and is it relly necessary since my pedal is hard.
 
#5 ·
I spent weeks trying to get my brakes working problerly again. The pedal was rock hard but it wouldn't stop worth a damn. New MC and booster (twice), and new calipers and hoses. Well, I finally broke down and decided to replace my original prop block and boy was I glad I did. The sucker was rusted up on the inside very badly. I tried to disassemble it, but only succeeded in getting the a few parts of it out. The main piston/plunger inside is stuck solid. The gunk that came out of it was nasty.

So... If you've already done the rest, I say replace the prop block.
 
#7 ·
Simple question. the 79-89 Repair manual says car may have proportioning valve located under the master cylinder. On my 79 there is nothing right under the cylinder but the two brake lines go downward towards the frame..Do I just follow the brake lines to see if there is a proportioming valve? Where is the valve usually located on a 79 if there is one?Car has front caliper brakes. I can pump fluid through the rear wheel bleed screws. Does this mean they are bled and I don't have to be concerned?
Padon the screw up on my previous post-I meant 79 not 72. I have one of each,They don't call me OLE george for nothing
 
#8 ·
Look down on the inside of the frame rail right about where the oil filter is on your block. It was a bit of a hassle to get mine out just because of clearance issues (hard to get a flare nut wrench onto the fittings in such tight quarters).
 
#10 ·
The old valve is "tripped" thinking the rear brakes had a failure, thus shutting off flow to them.
Now you have to trick it, with master full, and lid on, have someone loosen both front bleeders, and push the brake pedal as hard and quick as you can, I call it "2 foot'n it".
Don't let up until the helper tightens both bleeders, now pump it easy and slow, don't go all the way to the floor.
Now try to bleed the rear.:texas:
 
#11 ·
You actually need to push that pin IN, not pull it out. That pin is spring loaded from the inside, and it is tripp'd when it thinks there is a massive leak in the rear, so the pin pops out to stop the flow of brake fluid to the rear. Have someone push that pin IN using a pick or any small pointy implement, and hold it in while someone slowly presses the brake pedal. You may have to do it several times till the brakes are bled.
 
#15 ·
What is a "prop block"? I'm having brake problems as well. New booster, master cylinder, rear wheel cylinders, yet the car just doesn't stop worth a darn!


the proportioning valve/block is where you can adjust the bias front to rear with the fluid pressure...you will use trial and error to get the right pressure front to back, by adjusting it...driving it, braking hard...if the rear end locks up, adjust it untill the front end locks up before the rear brakes lock up (you really do NOT want the rear brakes to ever lock up, because thats when the rear end swings around like your bicycle did when you were a kid and locked the rear tire, and swung the rear around. Thats bad in a car
 
#14 ·
you might have air bubbles in your brake system. You'll need to bleed your brake system. Remember, fluid does NOT compress....air DOES. if you have air in your system, then you have no stopping power because it is compressing when you press the brakes and keeping your pedal pressure from pressurizing the fluid to the brake pads. Bleed it. Bleed it again. and Bleed it again till no air bubbles are present. Brake fluid is cheap. your front end is NOT.
 
#17 ·
welcome Joe

sometimes the brake hose will go bad, it will come apart on the inside and block the fluid flow..
it will make your brakes grab and jerk from side to side when you hit the pedal..
or
sometimes you can get a plug of rust that will stop flow on 1 side or the other..
that can happen in the combination valve on the front too..
or
sometimes just the bleeder screw will rust/plug up..


let us know a little more, maybe we can help more..

:texas:
 
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