Rear brake proportional pressure valve - brake bleeding

Discussion in 'Gen 1 & 2 - Suspension, Brake Systems, & Body' started by klaytonz, May 21, 2020 at 3:01 PM.

  1. klaytonz

    klaytonz New Member

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    Hi all, looking for any information about the rear brake pressure valve. Currently I have very little brake fluid flow to the right rear brake and no flow to the left rear. The lines and all else seem to check ok. I now get to the pressure valve and have searched for days on how this is supposed to work. I literally found nothing showing this thing working or how it works and what is supposed to move other than acting on suspension height. From the way it looks I would think the two pins sticking out from the rubber grommets (circled in red below) move in and out as the suspension rises and lowers to change the brake fluid pressure. At least that is tho only way I can think it would work as there are no parts moving except for the arm connected to the spring. The two pins are solid and do not move. Is this the issue or am I guessing wrong? If they are locked and should move is this serviceable? I see the whole part is obsolete and costs it’s weight in gold currently.

    I did try to remove the attached brake lines but just could not get the leverage from the puny wrenches that can attach in that small space. Fun!

    Thanks for any advice!

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  2. luigisho

    luigisho SHO Member

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    What year is your car? You're observation of how it is supposed to work is correct. If it is not functioning at all then you will probably have to replace it with a used unit. I do not think there are any new units still available. Usually the most common issue is the rubber hose from the solid line to the brake caliper. They degrade inside and swell and do not allow fluid flow.
     
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  3. Irish Pride

    Irish Pride Irish Inside Staff Member Super Moderators

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    The rear of the car needs to be on the ground when bleeding the rear brakes. If you have the car jacked up and the wheels/arms hanging, that will cause bleeding issues. Lift up each side with the jack and bleed with them compressed. I usually just back my car up a set of ramps and then bleed them.

    The problem is going to likely be the rear brake hoses. I've never seen a bad bias block. Remove the hose from the caliper and see if you get any fluid from it. If not, replace the hose. They can look perfectly fine but be collapsed on the inside.
     
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  4. klaytonz

    klaytonz New Member

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    Thanks for the replies. I did get the brake line off of the bias block at the output end for the left rear, top right connection. It tested good as fluid was flowing through so if it is stuck at least it is open to an extent. Now off to find a good flare nut wrench, that rubber brake line is stubborn!
     
    Last edited: May 23, 2020 at 2:59 PM
  5. RonPorter

    RonPorter Old Dude

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    The other thing to do is what many of us did. Disconnect the lever on the bias valve, and ziptie it up to mimic a level car. It's as useless as a bellybutton anyway.
     
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  6. SHOZ123

    SHOZ123 SHO Member

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    And start the engine so you get some boost for when you bleed the rear the brakes.
     
  7. Tbird6

    Tbird6 New Member

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    I installed plugs inside the valve and permanently removed them from the system along with upgrading to SS brake lines on my old 1993 SHO.
    A world of difference in the brake pedal feel and in braking performance!
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  8. RonPorter

    RonPorter Old Dude

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    I think that SHO Source sells the plugs for the valve, which is really the best solution, short of going through all of the trouble to pull the valve and replumb all of the lines.

    And those plugs have never been cheap, as it's a very odd thread and size that is not commonly available.
     

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