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  #1  
Old 07-11-2019, 11:48 AM
eldudderino eldudderino is offline
230 Tornado
 
Join Date: Jun 18, 2018
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Brake Bleeding Help

Hi, I have been trying to bleed these brakes for a few weeks now. It is a 1984 jeep J20 and the back brake line blew. I have tried the pumping and holding method and a vacuum bleeder with no success. I believe the proportioning valve has something to do with it. It seems the pin pulls out not pushes in. I have tried both methods listed above while someone pulled the pin out with no success as well. Any advice? How do I know if the valve is bad??
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Old 07-11-2019, 01:01 PM
SJTD SJTD is offline
350 Buick
 
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Idunno off hand which way the pin goes when it detects a rear failure but it should be in the normal centered position to bleed.

There's a tool to hold it there. Even if you start with it in the correct position the act of bleeding can cause it to move. If you do it slowly the pin might stay in the normal position
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Old 07-11-2019, 02:36 PM
eldudderino eldudderino is offline
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Quote:
Originally Posted by SJTD
Idunno off hand which way the pin goes when it detects a rear failure but it should be in the normal centered position to bleed.

There's a tool to hold it there. Even if you start with it in the correct position the act of bleeding can cause it to move. If you do it slowly the pin might stay in the normal position
I have tried moving the pin and not moving it and it still does not do anything. The pedal doesnt go to the floor either when you open the bleeder.
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Old 07-11-2019, 02:56 PM
SJTD SJTD is offline
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Maybe you've done this but to be systematic, start at the master and loosen the rear line. Pedal drops and fluid comes out? Do the same at the P-valve. Then after the P-valve, at the flex above the axle, etc. Until you find where the flow stops.
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Old 07-11-2019, 03:25 PM
SJTD SJTD is offline
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My book says in the p-valve description that the tool is required to bleed the fronts. It doesn't say it's needed to bleed the rears.

In the bleeding instructions it says to install the tool but that procedure bleeds both the fronts and rears not just the rears so Idunno if you need it or not.
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  #6  
Old 07-11-2019, 05:18 PM
wiley-moeracing wiley-moeracing is offline
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Start by bleeding the master cylinder first to make sure you have all the air out of it( bench bleeding is the best way).
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Old 07-11-2019, 07:05 PM
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nograin nograin is offline
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Quote:
Originally Posted by wiley-moeracing
Start by bleeding the master cylinder first to make sure you have all the air out of it( bench bleeding is the best way).
I agree.
When it comes to bleeding the rest, I don't find it neccessary to open the meter valve. Nor does the shop manual say to. Its only when pressure bleeding that it helps.

'Metering valve' slighly delays initial pressure to the front brakes. After 30 psi or so it opens. But that was enough to stop a typical pressure bleeder. The proportioning valve reduces the pressure to the rear brakes relative to the front and only starts to function at relatively high pressure (like 300 or 500 psi).
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Old 07-11-2019, 11:18 PM
SJTD SJTD is offline
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Doesn't sound like the master needs bleeding since he says the pedal doesn't drop when he opens a bleeder.
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  #9  
Old 07-12-2019, 05:49 AM
eldudderino eldudderino is offline
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Quote:
Originally Posted by SJTD
Doesn't sound like the master needs bleeding since he says the pedal doesn't drop when he opens a bleeder.


Before I put the rear line on the valve it did not have fluid running out of it. The master cylinder was full though.
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  #10  
Old 07-12-2019, 07:47 AM
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babywag babywag is offline
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Being a rust belt vehicle I would examine the bleeders.
I have seen many that were rusted closed.
Have also seen wheel cylinders that were completely filled with rust/crud.

If it was me I'd remove both rear bleeders, remove master lid, top off master and see if it'll gravity bleed.
If no fluid after a while start working backwards.
As in remove hard line connections @ wheel cylinders, then rear brake hose, etc., until you see fluid.

In decades of working on vehicles I have never had to touch/screw around with a prop. valve pin when bleeding.
In some cases have found that hammering the brake pedal HARD 1 or 2 times frees up the prop. valve if its actually the issue.

What back line "blew"?
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  #11  
Old 07-12-2019, 09:07 AM
wiley-moeracing wiley-moeracing is offline
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Again start by bleeding the master cylinder first, he has pressure on one side of the cylinder because they are separate, the other side can be full but still have air trapped in it. Once you have the master cylinder bleed then proceed to the farthest wheel cylinder, and do not let it run dry! You may find the seal is bad in that part. if it feels and looks good, let it gravity bleed out( this will take awhile but do not let it run dry). If nothing, try and blow through the lines, may have a blockage.
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  #12  
Old 07-12-2019, 09:17 AM
eldudderino eldudderino is offline
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I think I got it boys! I cracked every line that goes to the back and they all had fluid. The one wheel cylinder that is the farthest away just would not bleed so I have to get another new one....only 6 bucks so hey whatever..the rest bled fine. It was just the one bad one that I was having trouble with and didnt think to check the rest.
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  #13  
Old 07-12-2019, 11:17 AM
wiley-moeracing wiley-moeracing is offline
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Yeah.
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