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P-Valve or Perportioning vlave (sp/) **Ryan?**

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Burt4x4, Aug 17, 2004.

  1. Burt4x4

    Burt4x4 3/4 ton status

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    Ok so I have replaced my 72 brakes with 3/4ton stuff
    I bought the Booster and matching Master cyl.
    Now I was going to just use my P-valve BUTTTT the silly lines are reversed??
    I mean that the old master has the larger hole in front with the smaller hole in back? The New master has just the opposite. Now the wierd part is the P-vavle's inlets are big in front and small in back like the new master but the lines used have one end big and one end small /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif
    I'm confusing my self....Ok so maby if I just scrap the lines being used and make ones that will fit and all is good??
    So the back resavor on the master is for the rear brakes right? the front is for the front right?
    Man I think I had some crazy missmatch shiat on my rig????
     
  2. Burt4x4

    Burt4x4 3/4 ton status

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    I think I got that backwards
    Old Master = Smaller hole in front bigger hole in back
    New Master = Bigger hole in front smaller hole in back
    Old P-vavle = bigger hole w/3/16" line in front smaller hole w 1/4 line in back(thease lines are not normal, the one with the 3/16 line has a 7/16 head instead of a 3/8 head and the 1/4 line has a 3/8 head instead of a 7/16head??)
     
  3. BobK

    BobK 1/2 ton status

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    I believe the 3/4 + 1 ton stuff is reversed like that.At least that what it looks like in the manuals.
    Here's the 3/4+one ton stuff.
    [​IMG]

    and the 1/2 ton setup
    [​IMG]

    Either get the proper prebent lines or make you're own.
    I'd make my own.
     
  4. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    I donno.. my master cylinder doesn't look like either in those pics?
    [​IMG]
    Burt man, i dont know why you're having issues, my master cylinder and rod length were perfect and bolted up exactly the same to the 3/4 ton booster. It looks like i have a different master cylinder than you probably..
    When i replaced the MC years ago that was the correct style for my "1972 k5 blazer" ? /forums/images/graemlins/dunno.gif /forums/images/graemlins/screwy.gif
    *sending positive thoughts & good vibes*
    /forums/images/graemlins/rotfl.gif
     
  5. Burt4x4

    Burt4x4 3/4 ton status

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    hahah thanks for the vibrations my brotha.
    Your mast looks to have a smaller rear resavor? Mine are the same in size? My old one has a higher look to it like yours, the new one has a low profile look to it but the resavours are the same size??
     
  6. Burt4x4

    Burt4x4 3/4 ton status

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    Holy Moly!!! That is it!
    Damn! So I simply need to swip swap the lines front to back to make it look just like that pic!
    Thanks BobOOOO!!

    I have big book at home I can dust off and take a look see...

    Oh and as far as buying a new Pvalve looks like the dealer is the only one with one and they want 129 /forums/images/graemlins/yikes.gif /forums/images/graemlins/screwy.gif
     
  7. BobK

    BobK 1/2 ton status

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    Ya I ran into that when I did my rear disc swap.No one carried a factory replacement Prop. valve except the dealer.And they were priced like you mentioned.

    I'm not sure if the prop valve themselves were different between the 1/2 and 3/4,1 tonn stuff though.
     
  8. Muddytazz

    Muddytazz 1 ton status

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    I don't know if this helps at all or not, but on my 2nd gen burb, when I did my rear disk/axle swap, I left the stock 1/2ton prop valve in there and haven't had any issues. I did swap to a 3/4ton m/c and they are the same as the 1st gens, the fittings are reversed. From what I understand(have heard thru many a grapevines) is the reason that was done was because of the m/c piston bore/size. Now that story could be all wet behind the ears, but when I was thinking about it it sounded logical.
     
  9. Burt4x4

    Burt4x4 3/4 ton status

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    Thanks!
    Come to find out the inner most resavor is the 'primary' so having the front disks as primary kina makes sence. Olmost like the 1/2 ton did it wrong /forums/images/graemlins/dunno.gif
    pics
    [​IMG]
    see the bigger front onthe Pvalve
    [​IMG]
    see the smaller front on the old Master and how the old master is taller...
    [​IMG]
     
  10. stretch67

    stretch67 1/2 ton status

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    don't know if this will help burt? i used a 1974 3/4 ton prop valve and the front lines also. they bolted up fine i think the master cylinder booster i used was a 71 1/2ton 4x4 iirc the prop valve sits on front xmember under radiator.do you have a donor truck that you got the engine xmember out of? i also used the front swaybar xmember while i was making stuff fit i used the ORD swaybar disconnect, the handling was much improved good luck! lonnie /forums/images/graemlins/rotfl.gif
     

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