Brake questions

Discussion in 'The whoa and the sway.' started by JoeBlog, May 31, 2022.

  1. JoeBlog

    JoeBlog Platinum Level Contributor

    My 67 (drum/drum) lost fluid in the rear well of the master cylinder, and my vacuum booster is evidently where all the fluid went. I figure there’s pitting and/or corrosion in the cylinder that caused it, so I’m installing a new master and booster setup. My question involves the rebuild. I want to purge the entire system with denatured alcohol then blow everything out and let it all dry before filling the system with DOT-4 (synthetic) fluid. Of course, I’m gonna check all the hoses for collapse and wheel cylinders for any issues as well before I do all that. Does that sound appropriate? Am I missing something/doing something I shouldn’t? I’m sure this all happened because DOT-3 fluid collects moisture, and I want to rebuild things in a way that mitigates a recurrence later on.
  2. john.schaefer77

    john.schaefer77 Well-Known Member

    DOT 4 collects moisture same as DOT 3. Are you thinking of going DOT 5 (silicone)? Some folks refer to that as synthetic.
    If just going DOT 4 no need to flush system with alcohol. Checking out wheel cylinders and hoses is a good idea. They are all fairly easy to change and give you an excuse to check all the moving components.
    Max Damage and JoeBlog like this.
  3. CJay

    CJay Supercar owner Staff Member

    Dot 5 has its own set of pros and cons. My best advice is to keep the dot 3 or 4. Dot 4 just has a higher boiling point. Flush your brake fluid every 3 years and you'll never have a problem
  4. Redmanf1

    Redmanf1 Gold Level Contributor

    If you check some of the premium rebuilders will not warranty, there rebuild if used with Dot 5 fluid. Just something to think about...
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  5. Max Damage

    Max Damage I'm thinking about it!

    I would just flush it with the new fluid till it's all clean. That's what I have done repeatedly (different cars) and it's never been an issue. I wouldn't mess with the alcohol.
  6. Super Bald Menace

    Super Bald Menace Frame off oil changes

    I read somewhere that all brake fluid is synthetic and all but DOT 5 are hydroscopic (absorb water)
    JoeBlog and john.schaefer77 like this.
  7. Waterboy

    Waterboy Mullet Mafia since 6/20

    I buy Peak dot three synthetic brake fluid from Dollar General. It says synthetic on the label, unless they’re lying to me. I did what Max damage said, just keep adding fluid to it, until it all drains out nice and clear. My brakes work perfect on a 69, all drum Skylark.
    I got my brake booster from Summit. It comes with that nice gold looking plating, whatever they call it, and everything is working great!
    My master cylinder was leaking from the front brake section. Undoubtably going inside the brake booster. Got a new brake master cylinder under warranty.
  8. FLGS400

    FLGS400 Gold Level Contributor

    I debated on going to DOT 5 for a bit. Once I got into the disc brake conversion more, I decided to just stick with DOT 3, and it works great!

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