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Do we have Residual Valves? Where are they?

Discussion in 'The Garage' started by divorced, Dec 9, 2005.

  1. divorced

    divorced 3/4 ton status

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  2. K5er4Life

    K5er4Life 1/2 ton status

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    I dont think so, I only say that because when I did my rear discs I did alot of searching to see what kind of results people where getting in regards to how the brakes were reacting. And I seen alot of proportioning valve changes/mods, master cylinder upgrades...etc. And I have never heard anyone talking about a residual valve that came on our trucks. Maybe in the later years but defnitely not my 87 blazer or 86 crew cab have one.If you want to buy one tsm has them. Just scroll down to the residual valves on the page.
    http://tsmmfg.com/Brake_Accessories_others.htm#RESIDUAL%20VALVES
     
  3. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    There are two different uses for residual valves. The 10 lb valve is used to hold a residual pressure to the drum brakes to give a higher firmer pedal. The 2 lb valve is used in the disc when the master cylinder is lower than the calipers to prevent back siphoning of the fluid from the master.
    Out trucks never came with residual valves.
     
  4. sled_dog

    sled_dog 1 ton status

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    umm thanks for quoting the first thing you found on Google?

    Are we really certain our trucks never came with Residual valves? I've never gotten a conclusive answer.

    Residual valves are onl used with discs when the master cylinder is mounted lower then the calipers(thus the back siphoning mentioned).
     
  5. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    You like that! Amazing, that google thing.

    I took a scan of the 73-78 and 79-84 GM parts books, no residual valve is listed. For C,K,P,G vehicles. Mabey on '85 and up, but I highly doubt it. I scoured groups 4 & 5. Nothing. THere was a factory D-Shaft parking brake offered on P-Chassis though, a mini drum setup up. Sweet! Learn something new every day!
     
  6. sled_dog

    sled_dog 1 ton status

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    good to have a reference based answer to this question
     
  7. sweetk30

    sweetk30 professional hooker Premium Member

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    used to prevent back feed of fluid when master is lower than calipers/wheel cylders.
     
  8. ntsqd

    ntsqd 1/2 ton status

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    But did you disect a brake master cylinder?

    Usually the OE's put the Residual Pressure Valves (RPV) in the master cylinder. They're in behind the seat for the brake tube in each outlet port. The way to remove that seat is to run a tap, usually a 6-32 works well, into the hole in the center of the tube seat. It will eventually bind against the RPV bits and if you keep going it will extract the seat. Sometimes you have to go to a long screw the get the seats out. Once the seat is out the RPV bits will fall out of the m/c. If you've done a carefull removal job you can then put the seat back in w/o the RPV bits in place.
     
  9. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    I did. They had every part broken out in the master group. Nothing resembling a residual valve.
     
  10. ntsqd

    ntsqd 1/2 ton status

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    Interesting.
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    Not meaning to start something, I just searched and searched, I believe this was covered before, but I can't find it.

    I'm almost certain my service manual (no access to that for awhile!) shows that at least a couple of the multiple master cylinders listed for the trucks have a valve that is pressed into the seat where the brake lines seat.

    Take it with a grain of salt, like I said, I don't have my references to double check, and it's been a long time.
     
  12. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    I didn't check the service manual. I'll check that when I get home. I was looking at the parts books. I could have missed it. Alot of thier names don't make a heck of a lot of sense. I was looking for 'valve', 'residual', 'pressure', or any name I didn't know what it was in the master parts section. Didnt' see anything. But I've been accused of being a bad looker before.
     

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