When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
So my 77 was basically a barn find. Last tag was 98. The brakes were froze up. I replaced all calipers, master cylinder and small lines. I blew all the crap out of all lines. I have tried gravity, hand pump, shop vac, screaming and cussing . I got the front to act right but the back acts like the lines are plugged. So I blew them clear , twice. Both ways. Still no flow to the back. Side question, what are the two bleeder valves on the side of the master cylinder? Any ideas?
thanks
Did you bench bleed the MC before you installed it? If not, that may be your problem. I recently bled my brakes and used my Motive Power bleeder. Worked great.
Did you replace the proportioning valve? It's the rectangular "rod" with a bunch of brake line connections and one electrical connection below and behind the mastery cylinder? If it's frozen up I believe it can prevent fluid from flowing to the front or the rear.
I presume you bench bled the new master cylinder, correct? If not look up the procedure--it's not difficult--and be certain neither of the reservoirs ever goes empty.
The new master cylinder was just put in by the previous owner. He probably did not bleed it.
is there a way to bleed it in the car? My MC has two bleeder valves on the side. Are those for that? I can blow from MC to rack rear brake line but if that could still be it I’ll replace it tomorrow.
Did you try the two man pump bleed? At least to get started?
make sure brake light is out..if on splitter valve ve, distribution, proportion..... may be tripped..stab pedal to reset usually..
my rears were slow too..
Last edited by interpon; Feb 22, 2020 at 07:30 AM.
Either buy or make a pressure bleeder. I made one because I didn't want to wait for an order. Here we are 15 or so years later and it worked so well that I never bought one. Here are some ideas: https://www.corvetteforum.com/forums...y-version.html
Originally Posted by Texxracer
So my 77 was basically a barn find. Last tag was 98. The brakes were froze up. I replaced all calipers, master cylinder and small lines. I blew all the crap out of all lines. I have tried gravity, hand pump, shop vac, screaming and cussing . I got the front to act right but the back acts like the lines are plugged. So I blew them clear , twice. Both ways. Still no flow to the back. Side question, what are the two bleeder valves on the side of the master cylinder? Any ideas?
thanks
It is a proportioning valve or as some call it a combination valve the round cylinder part screwed into the back of the block is the proportioning part
As others have said, bench bleed the master cylinder. Your car does not have a proportioning valve. It has a distribution block. GM designed the bias in the system by having different size pistons in the front and back of the car. As such, no proportioning valve is needed. Sometimes the distribution block has to be reset. There is a tool that can do it and also method of doing it through the brake pedal. Jerry
I agree with the distribution valve being jacked......if your car does not gravity bleed....then something is wrong. You are trying to gravity bleed only one wheel at a time, right?
I only gravity bleed now....started doing it like 15 years ago....works everytime.....but no fluid means a restriction and if that is the case, even if you did get it bled, the brakes will not function properly.....
I will concede main part is a distribution block with switch. Proportion valve or nut as it is called in the manual is screwed in the back of the block going to rear brakes. That's why it is sometimes called a combination valve. It has 3 functions distribution,brake switch, and proportioning to rear brakes. Page 5-6 figure 8 in 1976 chevy service manual.
Bob
I will concede main part is a distribution block with switch. Proportion valve or nut as it is called in the manual is screwed in the back of the block going to rear brakes. That's why it is sometimes called a combination valve. It has 3 functions distribution,brake switch, and proportioning to rear brakes. Page 5-6 figure 8 in 1976 chevy service manual.
Bob
You would make a good politician. You tell people what everyone wants to hear.
YES. You can bleed it in the car. I really do recommend a pressure bleeder. I've used mine to help several of my friends who couldn't get their brakes bled for crap.
Originally Posted by Texxracer
The new master cylinder was just put in by the previous owner. He probably did not bleed it.
is there a way to bleed it in the car? My MC has two bleeder valves on the side. Are those for that? I can blow from MC to rack rear brake line but if that could still be it I’ll replace it tomorrow.
Last edited by carriljc; Feb 23, 2020 at 11:35 AM.
Here's the text from my 80 shop manual. At any rate, it sounds like the combination valve needs to be reset before you'll be able to bleed the rear brakes. It's a bit of a catch-22 if the valve has latched and you can't build pressure in the rears.
Not sure what you mean by that. All I was trying to do was tell people what valve was. If you read further posts I believe I am right
response to headsup in northern michigan where I happen to be from
Last edited by robertwg; Feb 23, 2020 at 08:57 PM.
Tex, I have a very similar issue. I replaced just about every part of the brake system on my 76 recently, and went to bleed the brakes with my Motive pressure bleeder from the master cyl side. I had bench bled my master (done this before on other cars) and could only get a trickle out of both of my rear calipers. Both fronts had brake fluid shooting out from the pressure, but I couldn't get the rears bled. Tried starting the car, letting it warm up so the vacuum would be nice and normal, and I had a spongy pedal.
From what i am reading my proportioning valve (or whatever you want to call it) has the internal valve towards the rear. When that valve goes to the rear it is similar to a hard brake situation, and the valve limits the flow to the rears as to not lock up the rear tires. I was not aware of the tool that keeps this from happening, but have since ordered one. If I can get my valve back centered I will use the tool and bleed them all around again. The vendor that sells the tool, POL, replied to my email and suggested this..... before doing anything turn the ignition on and put a test light on the switch on the proportioning valve. It should show 12 volts, or light up your test light, implying that the valve is towards the rear (or simply not centered). I have been working double shifts so I this is where I am at, and have not tested this yet. Anyway, if it shows lit up, then they say to crack both front calipers and stomp the brake pedal, which should center the valve, and the light should be off. If so, they told me to replace the sensor with the tool and pressure bleed the brakes. I hope this coming weekend to do just this procedure and get my car back on the road.
If anyone more knowledgeable about this whole system has any input or corrections, please do so - I am looking for anything that will help me also. Short of ordering another proportioning valve, I hope to center the new one on the car and be back in action this coming weekend!
Good information. At least I don’t feel stupid now. I can’t get to my car this weekend but I’m ordering a new p-valve anyway. I’ll post what finally works for me. Thanks to all for the input.
dave
Bleeding my brakes
