Bleed brakes on 94 Suburban

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  #1  
Old 07-07-05, 11:02 AM
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Bleed brakes on 94 Suburban

This car purchased two weeks ago. The brake fluid is dirty and I tried to bleed the brakes but the bleeder screws on the rear wheels snapped off so I replaced the wheel cylinders. Now when I try to bleed the brakes there does not seem to be any pressure in the lines to push the new brake fluid through.
The Surburban manuls I have mention a combination valve that must be held open. There is a little rubber capped knob on the combination valve but I don't have the tool mentioned in the book. Am I supposed to pull these knobs open and then stick something in betweed to keep the knobs open as I bleed the brakes?
TIA, Frank C.
 
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  #2  
Old 07-07-05, 11:19 AM
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If the prop. valve is the problem, you should be able to equalize it by applying the brakes with 1 front and 1 rear bleeder open.
 
  #3  
Old 07-07-05, 02:08 PM
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Bleed brakes on 94 Suburban

Let me explain myself better because I think there is an additional problem I thought I could overlook.
The brakes worked fine when I got the car. Then very shortly the brakes started to weaken with a spongy touch. The brake fluid was dirty so I started by trying to bleed the brakes. However the two back bleeding screws broke so I replaced the wheel cylinders. Then in bleeding the brakes I accidently let the front chamber of the master cylinder run down to the bottom.
Now I assume I have to bleed starting from the master cylinder. How do you bleed the master cylinder? Do I just take off each line at the cylinder while someone pushes in the brake pedal and then shut the connection when I get a good flow? I need step to step information for me to understand.
In bleeding the brakes, in general, a book indicates the combination valve has to be left open. I think the combination valve is farther to the left (drivers side) and downward from the master cylinder. This combination valve has a rubber cap on either end of it. Underneath these rubber caps, which cannot be pushed in to open the valve, is this where the combination valve has to be pushed in if I take the rubber caps off? Can these rubber caps be pried off? The book indicates an assistant can hold in the metering pin of the combination valve while the brakes are bled. So is there something the "assistant" can push in once these rubber caps are taken off?
TIA, Frank C.
 
  #4  
Old 07-07-05, 02:33 PM
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If all this started due to a spongy pedal, you may have a bad master anyway. Bleeding it on the truck can be done, as long as it sits level. Simply loosen the fittings (do not remove), have your assistant apply the pedal, tighten the fittings, release the pedal. Wait 10-15 seconds between each application. Do this until you get no more air. As far as centering the valve goes, the method I described should work. Once you get the master bled, do as I described. Once or twice should center the valve. Once that is accomplished, I would gravity bleed it from there.
 
  #5  
Old 07-07-05, 03:18 PM
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Bleed brakes on 94 Suburban

Do you mean open one bleed valve on the front disk brake calipers and another bleed valve on the back of the rear brake shoes?
The master cylinder's two lines go to the top of the so called combination valve. The two bottom lines out of the combination valve go to the rear and front inlet fittings on the Brake Pressure Modulator Valve (BPMV). Are these fittings what you are referring to?
Then there's a right and left bleed valve below the rear and front inlet fittings-did you mean open these up?
Once we get to where I open up the fittings isn't it going to be a bit tricky opening up two valves at once? So would I need two wrenches and a helper on the second wrench? ?
TIA, Frank C.
 
  #6  
Old 07-07-05, 03:31 PM
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To bleed the master - the 2 fittings at the master. Loosen the fittings 1-2 turns, have assistant depress the pedal, tighten the fittings back up while pedal is still depressed. Release the pedal after fittings are tight. Repeat these steps, with 10-15 seconds between cycles, as many times as necessary to get clean fluid with no air. Don't concern yourself with the BPMV or the prop. valve, neither should require bleeding. After you have the master bled, open 1 front and 1 rear bleeder (caliper, wheel cyl.) and depress the pedal. That should center the prop. valve. If necessary, repeat that step until the valve does center. From there, gravity bleeding the wheels should be possible.
 
  #7  
Old 07-08-05, 09:09 PM
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Bleed brakes on 94 Suburban

Had difficulty finding someone at home to assist when I had a chance to bleed the master cylinder. After I bleed one front and one rear wheel how do I tell the prop. valve has centered?
 
  #8  
Old 07-08-05, 09:11 PM
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You'll have fluid flow at the rear wheels.
 
  #9  
Old 07-09-05, 06:54 PM
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Bleed brakes on 94 Suburban

It worked like you said.
Prior to this car I had an 86 Suburban. I was unfamiliar with opening up two bleed screws at the same time.
I had my daughter at the brake pedal and another person at the front wheel to bleed that brake so I would not have to get up and go to one of the rear wheels and get back down to open and tighten the second bleeder valve.
I loosened up the two bleeder screws at the master cylinder about 10 times-I just was not sure I was getting a clean flow, besides I wanted to get clean fluid in the whole master cylinder.
Centering the prop. valve went smoothly as did the regular bleeding of the brakes.
The pedal is still low but the rotors and the drums are both ready to be discarded. If I had enough experience to think ahead I would have bought the rotors and new drums ahead of time and have the job done by now. The shoes and pads are borderline so I will buy new sets and do everything tomorrow.
Thanks for the help.
Frank C.
 
  #10  
Old 07-09-05, 07:25 PM
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Glad to hear it worked out for you. That method for centering the valve will work on anything with an external prop. valve (at least it's never failed me).
 
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