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Thread: Box master cylinder: super stupid question

  1. #1
    Member a_d_a_m's Avatar
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    Default Box master cylinder: super stupid question

    I am POSITIVE that this is a dumb question and I apologize, but I am vexed.

    A fitting on the Squire's MC is leaking. Of course, I didn't take a picture of it before wrapping it up for its winter slumber. So I'll just have to describe it as best as possible.

    It's the fitting that goes into the port in the middle of the passenger side of the unit, shown here.




    The leaky fitting LOOKS like what is in the Allstar box, shown here.





    My buddy thinks there is some sort of check valve or prop valve in there. I don't know that I believe it.

    Someone able to point me toward what I'm looking for at the parts store, or provide any additional wisdom?
    '91 LTD Country Squire LX | '04 CVLX ($200 winter beater) | '03 SAP P71 | '03 Marauder

    formerly: '02 MGM, '04 MGM, '04 MGM v2.0, '04 MM, '07 P71 w/5-speed

  2. #2
    I post a lot...
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    likely it is the combination valve for the rear drum brakes. It is a proportioning valve to balance front disks to whatever size drums were on the car. It is also a residual pressure valve which keeps a few lbs. of pressure on the rear system so the drums apply in synch with the front disks.

    Is the rear converted to disk? If you don't have drums any more you don't need/want the pressure component at all. As far as proportioning I added an adjustable proportioning valve. Also gutted the component you mentioned and drilled out a slightly larger hole in it.

    This pertains to an 89. A 91 may be different but still had drums so basic functions should be the same.
    "X" car 89 Colony Park LS Mods>Engine delete, SS duals magnaflow hflow cats, 2010 Must GT mufflers, auto air shocks, Posi, Tran cooler, big front brakes, 03+ rear disks, Large 3g alt, Tripminder, GS grill, 86 seats, 16" HPP wheels, winter boots=96 Cartier wheels, 215-65/16 Goodyear ULTRA GW3 snows, pi rear sway, alum driveshaft.
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    Member WagonMan's Avatar
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    You are correct, that is a proportioning valve. If you can't find a new one, I have some used ones. WagonMan
    Attached Thumbnails Attached Thumbnails Snapshot_20191128.JPG  
    1990 Colony Park
    1970 HEMI Superbird

  4. #4
    Member a_d_a_m's Avatar
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    Quote Originally Posted by jaywish View Post
    Is the rear converted to disk? If you don't have drums any more you don't need/want the pressure component at all.
    I still have drums out back.

    Quote Originally Posted by WagonMan View Post
    You are correct, that is a proportioning valve. If you can't find a new one, I have some used ones. WagonMan
    Appreciate the info and offer.
    This seems like something that should be available on the aftermarket and a parts store should be able to source. If not, I will be in touch to buy one off of you.
    '91 LTD Country Squire LX | '04 CVLX ($200 winter beater) | '03 SAP P71 | '03 Marauder

    formerly: '02 MGM, '04 MGM, '04 MGM v2.0, '04 MM, '07 P71 w/5-speed

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    Member a_d_a_m's Avatar
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    So far, all I'm seeing online is valves for the E/F series vans and trucks.
    '91 LTD Country Squire LX | '04 CVLX ($200 winter beater) | '03 SAP P71 | '03 Marauder

    formerly: '02 MGM, '04 MGM, '04 MGM v2.0, '04 MM, '07 P71 w/5-speed

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    Member WagonMan's Avatar
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    I unscrewed the one I took the picture of, It has an O-ring where it meets the master. Check that first. WagonMan
    1990 Colony Park
    1970 HEMI Superbird

  7. #7
    Member a_d_a_m's Avatar
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    10-4
    Really appreciate the information.
    The car is wrapped up for the time being, but I will open it up come springtime and check it.

    Thanks.
    '91 LTD Country Squire LX | '04 CVLX ($200 winter beater) | '03 SAP P71 | '03 Marauder

    formerly: '02 MGM, '04 MGM, '04 MGM v2.0, '04 MM, '07 P71 w/5-speed

  8. #8

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    Quote Originally Posted by WagonMan View Post
    You are correct, that is a proportioning valve. If you can't find a new one, I have some used ones. WagonMan
    Hi, I just saw this post. I would like to have one of those valves also, just in case (as a spare). How much for it? Would you ship to 33126 (Miami, FL). PM if you are interested in sell one. Thanks!

  9. #9
    Domestic Tourist Lincolnmania's Avatar
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    sometimes new master cylinders come with them.

    1986 lincoln towncar signature series. 5.0 HO with thumper performance ported e7 heads, 1.7 roller rockers, warm air intake, 65mm throttle body, 1/2" intake spacer, ported intakes, 3.73 rear with trac lock, 98-02 front brake conversion, 92-97 rear disc conversion, 1" rear swaybar, 1 3/16" front swaybar, 16" wheels and tires, loud ass stereo system, badass cb, best time to date 15.94 at 87 mph. lots of mods in the works 221.8 rwhp 278 rwt
    2006 Lincoln Town Car Signature. Stock for now
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    1986 Toyota pickup with LSC wheels and 225/60/16 tires.
    2008 Hyundai Elantra future Revcon toad
    1987 TriBurner and 1986 Alaska stokers keeping me warm. (and some pesky oil heat)

    please be patient, rebuilding an empire!


  10. #10

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    May be. But I have installed 2 MC (the first one was a Wagner, back in 2005 or 2006) and some months ago I replaced that one with a Bendix unit. None of them came with that valve. That's why I would like to have a spare.

  11. #11
    Member a_d_a_m's Avatar
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    I have not seen any in the parts stores nor online that came with them. Not saying they don't exist, just that they're rare.
    '91 LTD Country Squire LX | '04 CVLX ($200 winter beater) | '03 SAP P71 | '03 Marauder

    formerly: '02 MGM, '04 MGM, '04 MGM v2.0, '04 MM, '07 P71 w/5-speed

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    Member WagonMan's Avatar
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    1990CROWNVIC, I sent you a PM, WagonMan
    1990 Colony Park
    1970 HEMI Superbird

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