Bleeding brakes after Hydro conversion

D

deboeWE4

Member
Joined
Oct 27, 2011
In the process of doing the hydroboost conversion and I'm trying to bleed the rear brakes but the plunger on the proportioning valve won't budge.

I tried bleeding without the plunger pushed in and got no fluid at all. I've read a ton of posts about the bleeding procedure and a few mentioned that the plunger wouldn't move but I didn't see any solutions other than "you don't need to mess with that plunger." Obviously that's not the case for me. Any help would be greatly appreciated.



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I didn't do anything with the proportioning valve when I bled mine.
Did you bleed your master cylinder?
When you bled did you get anything(air) out or are you saying nothing comes out? What does the pedal do, hard , soft, no resistance?
Did you "burp" the power steering pump?
What master cylinder are you using?

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I'm using a Cardone reman master cylinder from a 81' Eldorado. I jacked the rear of the car to get the master level and bled until the bubbles stopped, then did 10 more brake pumps to be sure there was no more air trapped. The brake pedal isn't hard but there was resistance. I emptied out the power steering reservoir but did not "burp" the pump. Hadn't heard of that before, is that something I need to do?
 
I jacked up the front, topped off the power steering reservoir, and turned the wheel lock to lock several times to get the air out of the system.
Sounds like you got the master cylinder bled. I put a piece of 2x4 under the pedal to prevent my helper from bottoming it out.
I opened up both rear bleeders and had my helper pump the pedal several times to get the old fluid out. Then we bled until we got clean fluid. Be sure to keep topping the master as you bleed.


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its my understanding that the plunger being pushed in is what allows the rear brakes to operate, do you think if I open both rear bleeders and pump the brakes I'll get fluid? I'm probably going to GBody tomm to get a brass proportioning valve anyway so hopefully that will be an easy fix if nothing else works.

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How do the rear brakes work in regular operation? What pushes this plunger in when driving the car?
I guess I'm not understanding how it works.

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There has to be a certain amount of pressure in the line before it goes past the proportioning valve. Since you cant get any pressure in the line with air in it the valve has to be held open to bleed. It's a 2 man job unless you make a tool to hold the plunger in. It only moves about 1/16" as I recall. The valve should be brass. Buick had a recall on the steel ones over 20 years ago.
Ill find the tool I made and post a picture of it.
 
Here's a picture from the service manual and of the tool made from a piece of angle aluminum.View attachment 203855View attachment 203855
photo.JPG
 
I happened to have a bolt that was just the right length to keep the plunger in... wedged it between the plunger and the frame rail. IIRC, Cedar Crest speed labs has a nice Hydroboost install write up. Their instructions were spot on.

To prime:
  1. Fill the master cylinder to spec with new brake fluid.
  2. Fill the power steering reservoir with new power steering fluid.
  3. Crank the car for several seconds to fill and prime the hydroboost booster then check the power steering fluid level. Fill as needed.
  4. Reconnect the orange ECM wire and start the car.
  5. Flush air out of the system by turning the steering wheel from stop to stop twice.
  6. Shut off the car.
  7. Relieve system pressure by depressing the pedal five times.
  8. Check the power steering fluid level and fill as needed.
  9. Repeat steps 5-8 two times
 
I didn't run mine out. I just disconnected the old and installed the new and used new fluid to push old out. Makes sense why I didn't need to depress the prop valve.
Great tech on the tool to depress the valve and explaining what it does.
Get em working and you will know why people go to h boost.

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I'm trying to bleed without the plunger pressed in and I'm getting 95% air with a couple drips of fluid every now and then. Been at it for about 45 mins. Not sure if I'm accomplishing anything. I'm trying to post a pic of the proportioning valve so someone can confirm that the plunger is not in.

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Here's the plunger, it should be in further than this correct?

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If I was having the problem I think I would crack the feed line and try to get fluid out ahead of the valve. How did the fluid get out of the line above the valve?
If I didn't get fluid at that point maybe there is blockage above that. Some how fluid must move through the line or the brakes don't work, at least that's how I understand it.
Not sure on the prop valve. Does the plunger move at all? Maybe a clamp or something. C clamp?

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That's a really good idea to crack the feed line. The plunger doesn't move at all, even tried a C-clamp and got nothing. I'm getting a brass prop valve anyway since it should have been replaced 20+ years ago.

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Does the plunger pull out at all? Maybe it is already in all the way. Not sure. Though I would think with fluid above and how much psi brakes make something should happen.
Crazy how stuff seems to crop up when working on stuff.

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I can just barely pull it out about 1/16th of an inch but it pops back to where it is in the pic like its under tension from a spring. I just bought a brass valve and the plunger on it pushes in to the point it sits flush with the unit and mine definitely doesn't go in that far.

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Must be crudded up inside.
My next thought is that the mc is bad, but maybe the new prop valve will solve the problems.

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Welp... changed the prop valve and still nothing. Really hope its not a bad master :-/

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Did you press pedal with line off prop valve? Not sure you are getting fluid to the valve. Maybe blow through the line to make sure it is clear. Careful where you point it, that fluid removes paint.

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I'm gettin fluid through the lines all the way back to the rear wheels but not through the bleeders so I'm guessing the rear wheel cylinders are bad. I'm bleeding the front brakes now with no issues so I'm assuming the master cylinder is functioning properly. Unless anyone has any other thoughts I'll probably just get some new wheel cylinders and see if that works. I'm sure mine are 26 yrs old so replacing them isn't a bad idea anyway

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