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Thread: Proportioning Valve Removal

  1. #1
    Some Boost
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    Proportioning Valve Removal

    Okay, I hate to be stumped by this. Everything is going well on my brake rebuild, I've rebuilt the master cylinder (glad I kept the aluminum one), and replace the calipers with all steel piston versions.

    I have the kit to do the proportion valve rebuild, and I even have all of the lines removed from the proportion valve. But I cannot find a bolt or anything holding it on.

    What am I missing, how do I remove the brass block from the frame?

  2. #2
    Some Boost
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    Found, two bolts right on the other side of the strut tower. I blame only myself.

  3. #3
    Red Captain MikeFleming's Avatar
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    OK, you found it. If you hadn't found it yet, I would tell you it's held on by double-sided sticky tape. Just for fun.

    There are two studs on the backside of the PV body that you access on the wheel well side.
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  4. #4
    Some Boost
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    If you had said double sided tape, you would have a good chance of being right still from the things I've seen from the previous owner . That said, I'm the one with two 40 amp relays tucked loosely behind the battery to convert the inverted "off when on, and on when off" LA3 fan signal to a direct current.

    I've driven this car for probably 3 - 5 weeks total in the 8 years I've owned it, with the brakes being the last critical thing to solve (if A/C in the AZ summer isn't critical).

  5. #5
    Red Captain MikeFleming's Avatar
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    Yep. And we're just about to enter another non-cold season. Time to get out those short-sleeve shirts again.
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  6. #6
    Some Boost
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    Okay, most of the way in the rebuild. Not for anything is that inner stem coming out (the one without the spring).

    It turns, and I've even taken a screw driver and just kept turning it hoping to get it to loosen up.

    I've soaked it in B-12, goo-gone, alcohol, penetrating fluid and ammonia. I've injected all of them into the brake fluid switch hole to try to get the internal components as well.

    I've put a lot of force on it to where my small pliers are chewing up the end.

    I'm about to put it in the oven and try to find out what temperature the o-rings melt at. Perhaps brazing something at the end and using a slide hammer....

    Any advice?

  7. #7
    Red Captain MikeFleming's Avatar
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    That "piston" thjngie is aluminum, iirc, as is the PV body (the body is anodized, I sis==uspect the piston is also). So brazing will be difficult.

    Might try a couple days soaking in r=fresh brake fluid to see if that'll loosen it up. After soaking, gently tap it inwards to see if it wil lmove at all. Then slowly apply hydraulic pressure on the front port with the fail switch port and any other outlets plugged to see if it can be gently persuaded to come out.

    Be VERY careful about scratching the bore in the housing (probably too late though). Those bodys are NLA.
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  8. #8
    Some Boost
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    So I turned my attention to the other side, the one that came out easily, to see if it could give clues as to why the piston is seized.

    And ... after cleaning it with ammonia and a nylon wire brush it is clearly not just dirty but cankered across the bottom.

    I might try to have it sleeved, but looking at whatever corroded the bottom, I don't think the other side is salvageable anymore.
    pv_svo_bad-zoom.jpg
    Attached Images Attached Images

  9. #9
    Some Boost
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    I have two possible replacements sourced, but lets talk about the possibility of doing a PV delete...

    From what I can tell, Maximum Motorsports sells a PV delete kit for 87-93 that is just a set of two adapters from the master cylinder lines to the brake lines.

    But like all pre-87 cars, the SVO has separate lines for the front brakes meaning it has three brake line fittings instead of just two.

    Some old posts on old forums suggest some have found a combination of a hydraulic T junction plus a fitting adapter can work for pre-87's. Some also simply gut the PV.

    Then they use something like the Wilwood PV, installed on the passenger side where the rear brake line junction is. Seems very popular and reliable, but Wilwood doesn't suggest using it for the Highway.

    On one hand, seeing how fouled this PV wound up, I have diminishing faith that if I bought a used one that it would be serviceable. Add to that, I've found a few other posts where people struggled with getting that stem out of their PV as well, so this problem is not unique to my car.

    On the other hand, a cobbled set of adapters and a PV that is reluctantly recommended doesn't inspire much faith either.

    If it makes anyone feel better, the 85 S12 that is my daughter's project has a short in the temperature sensor line that seems to be thwarting the ECU from sending a fuel injector signal. So it isn't like there are greener pastures anywhere close by.

    Does anyone happen to know the fitting sizes on the PV that I would need to replicate with adapters?

    What is the common wisdom on the overall daily drivability of an aftermarket adjustable PV?

    Thanks

  10. #10
    Red Captain MikeFleming's Avatar
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    THat corrosion probably happened from 20-year old brake fluid with 20%+ moisture content. Brake fluid is a maintenance issue.

    I would go with the Wilwood Manual PV or similar. Find or build an adapter that connects the front brake part of the MC to both front caliper hard lines and connects the rear MC line to the rear line. That then goes across the firewall pinch weld area to the newly mounted PV.

    Then spend a little bit of time tuning the rear PV setting.
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  11. #11
    Some Boost
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    I'm guessing that these parts would work to connect the lines if I delete the old PV ...

    Dorman: 785-434D x 2, 785-436D, 785-310

    That is assuming the brake lines are 3/16" (with 3/8-24 thread inverted flare fittings) while the lines from the Master Cylinder are 1/4" (or at least have the 7/16-24 thread fittings in common with 1/4" line).

  12. #12
    Some Boost
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    Here are the parts mentioned above, assembled together.

    pv_delete.jpg

    1) I chose the 3/16" as the base with 1/4" adapters where needed. It may have been more efficient to choose a coupler and T junction for 1/4" line fittings (7/16-24 threads) and simply use adapters at the bottom to reduce to 3/16" line fittings. It would have used one less fitting.
    2) As it is, I could have re-used the coupler from the rear brake line (3/16" line fittings) at the passenger pinch weld too, since I'm replacing it with a Wilwood PV.
    3) I also suppose I could have used a T junction instead of a coupler, and integrated the brake switch.

    I think it was $52 altogether including shipping from RockAuto for the brass and the Wilwood store on Amazon direct for the PV.

  13. #13
    Some Boost
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    All installed now, I am contemplating if I need to build a bracket to hold the Ww PV. Seems plenty sturdy just supported by the steel brake lines.

    Some thread I read, and barely remember, calculated that the front calipers have about twice the volume as the rear, and the proportion between them was close to 70/30. I am not sure the PV progression is linear, or if that calculation is really a good basis for tuning.

    I noticed it is about 10 threads from fully closed to fully open on the PV valve, so I put it at three full turns away from fully closed (about 100psi). Sure enough the front brakes lock up before the rear (I tested on pavement and dirt).

    I might try backing it out more, but for now while not optimal it seems in the safe zone.

    I woke up feeling much like Inigo Montoya when he finally fulfilled his life's mission of revenge. Now that I've finally driven the SVO again, and it is no longer a derelict sitting behind the fence on the side of the house, what do I do now?

  14. #14
    Red Captain MikeFleming's Avatar
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    The PV works on pressure, not volume. THe MC makes the volume while the PV limits the flow qnty to limit / manage pressure.

    When at teh Bondurant School, we would set the rear PV valve to 90% front for the first day, then slowly bring it up to 70, then 50% as students learned proper braking control entering corners. The more lively the rear, the more attention s required. As you noted more front is safer.

    [quote] ... what do I do now? p/quote]

    Paint. That'll keep you busy for a while.
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