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!

The little pin on the prop valve needs to be pressed in while bleeding the rears. I'm not exactly sure of the proceedure, but its in the 72 service manual and I believe in the Haynes Manual also. How far "in" is the pin? I'm sure that it can cause problems. FYI - the replacement valves look nothing like the original but do work well.

Thanks for the reply. The pin is ALL the way in. It is flush with the base. I've tried a magnet, prying, vacuum. Anything to get it to pop up and it won't.

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.

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.

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.

I didn't need to bother. I used my pressure bleeder. It doesn't create enough back pressure to close the valve.

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

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


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).