67 GS drum brake question

Discussion in 'The whoa and the sway.' started by Gary Bohannon, Jul 16, 2022.

  1. Gary Bohannon

    Gary Bohannon Well-Known Member

    A friend put dot 3 in my master cylinder to bleed the brakes while I was gone. I use dot 5, so I flushed it out and chased it with denatured alcohol as described on a Corvette site. Then I learned I may have damaged the seals'
    I'm replacing all the cylinders. Blowing out the lines and putting new Dot 5 in.
    What about the residual valve?
    Is there any rubber in it?
    Where do you get a new one for all drum brakes?
    It's confusing on the web. No proportioning valve, right?
     
    Last edited: Jul 16, 2022
  2. Max Damage

    Max Damage I'm thinking about it!

    I think if these cars had "residual valves" from the factory they are built into the masters Cylinder?

    I can't think of there being any discrete (separate) valves for this in a drum brake car?

    Are you replacing the master also?
     
  3. Gary Bohannon

    Gary Bohannon Well-Known Member

    Yes, a master and all 4 wheel cylinders.
    I have new braided lines and eliminated the rubber there.
    I'm hoping there is nothing to be damaged if my car only used a residual valve or a distribution block. I just don't know what is inside them.
     
  4. Gary Bohannon

    Gary Bohannon Well-Known Member

    Will a master cylinder for disk brakes (with bleeders) work on my drum brake system?
    It has equal fluid pots and lid domes.
     
  5. Redmanf1

    Redmanf1 Gold Level Contributor

    Check the bore size of the two master's.
     
  6. wkillgs

    wkillgs Gold Level Contributor

    Gary, if you have a '67 chassis manual, there is a great description and some cutaway pics.
    There is a 'check valve' in the master cylinder on drum applications. It's purpose is to maintain 8-16# of pressure in the lines and wheel cylinders in static conditions..... this keeps pressure on the wheel cylinder seals to keep out air and prevent fluid loss (I just learned this!). I don't think there is rubber in the check valve. You may be able to remove it/them to inspect it. It's not used on disc brake circuits.
    The distribution block only has the piston for the brake warning switch. If there is a pressure loss in the front or rear, the piston moves and sets the dash warning light. I doubt there is any rubber in it.
     
    john.schaefer77 likes this.
  7. Gary Bohannon

    Gary Bohannon Well-Known Member

    Thankyou very much.
    Very helpful info.
     
  8. lemmy-67

    lemmy-67 Platinum Level Contributor

    DOT 5 with front drums? Seems like overkill. I converted to front disc, and get good pedal with DOT 3.
     

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