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Technical Brake System Issues.

Discussion in 'The Hokey Ass Message Board' started by 34Joe, Oct 21, 2021.

  1. So it's not a situation where the master cylinder isn't getting full stroke then? 20211103_202315.jpg
     
  2. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    I am using Valvoline Synthetic Dot 3 & 4 brake fluid. This is the same type I have always used.
     
  3. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    It appears to be getting a full stroke which I confirmed when I pedal bled the system originally .The system has never bled well using the brake pedal. It likes to be power bled , probably because of the booster.
     
  4. gimpyshotrods
    Joined: May 20, 2009
    Posts: 19,919

    gimpyshotrods
    ALLIANCE MEMBER

    Not mixed, I hope.
     
  5. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    Not mixed, I am just reading what it says on the container.
     
  6. gene-koning
    Joined: Oct 28, 2016
    Posts: 2,831

    gene-koning
    Member

    I want to be sure that I understand the issue you have when the brakes are applied is with the brake pedal in relation to the floor and has nothing to do with how the brakes function, correct?
     
  7. Wanderlust
    Joined: Oct 27, 2019
    Posts: 470

    Wanderlust

    Personally I would not be 100% positive about a “new” part working correctly, lately. I’ve had better luck with parts that were cleaned up and reused or repaired
     
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  8. primed34
    Joined: Feb 3, 2007
    Posts: 1,240

    primed34
    Member

    Amen to that.
     
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  9. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    The brake pedal at rest is 7 inches off the floor. When the brakes are applied the pedal stops at approximately 2 and a half inches off the floor. The brakes do not lock up, no matter how much pressure is applied.
     
  10. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    I agree, as this is the second booster and master cylinder that I have installed, each time having to have the system power bled ,costly, and ending up with the same results.
     
  11. WZ JUNK
    Joined: Apr 20, 2001
    Posts: 1,766

    WZ JUNK
    Member
    from Neosho, MO

    Two simple test I use when I test the booster and master cylinder. This may be old news, but I am old, so I can repeat myself without feeling bad.

    Pump the pedal a couple of times and hold pressure on the pedal while starting the engine. The pedal should drop a small amount and you should clearly feel it drop. If it does drop, then the booster is working.

    To test the master cylinder, I pump it several times, then hold a lot of pressure on the pedal. If the pedal slowly moves down over a minuet or so, and you have no external fluid leaks in the system, it is a good indication your fluid is bypassing the internal seals in the master cylinder and the master cylinder is bad.

    One of the problems with diagnosing the brake system is that a very small amount of fluid moves in the system when it operates. Even a very small amount of air or a small leak can cause big problems. I have found that most fittings made today, such as line size adapters or pipe to double flare adapters are a one time use fitting. The metal is so soft that the seating area is deformed the first time it is used. I bought special conical seals to use in these fittings. These seals are available on Amazon but none of my local parts sources sell them.
     
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  12. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    Good info is good info. Checked everything underneath again today, nothing unusual. Took it out for a test ride, no difference. The brake pedal is solid, but low and the brakes still will not lock up.
     
  13. Mimilan
    Joined: Jun 13, 2019
    Posts: 1,100

    Mimilan
    Member

    Have you checked the line pressures all round? [at the bleed screws]
    And are you running a proportioning valve?
     
  14. Hyvolt
    Joined: Jun 12, 2016
    Posts: 279

    Hyvolt
    Member

    As stated above, I had the same issues with a project in the past. I bought an inverted flare plug and works from the Mc to the wheels, insuring a hard pedal at step. It eventually boiled down to the fact the the Mc was below the floor, and almost even with the calipers. It was just air.
     
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  15. gimpyshotrods
    Joined: May 20, 2009
    Posts: 19,919

    gimpyshotrods
    ALLIANCE MEMBER

    Have you put a fresh master cylinder in yet?
     
  16. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    Line pressure is good at the bleeders. I do not run a proportioning valve .
     
  17. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    My Mc is below the floor also. The system has been pedal bled several times and has been power bled at least three times .The outcome is always the same, low brake pedal, and unable to lock up the brakes.
     
  18. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    I have put two new master cylinders in , purchased from two different places, and two power boosters, and the outcome is always the same.
     
  19. brigrat
    Joined: Nov 9, 2007
    Posts: 5,496

    brigrat
    Member
    from Wa.St.

    "Line pressure is good at the bleeders. I do not run a proportioning valve.
    What is "good line" pressure to you, what pound number in each corner?
     
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  20. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    Moot point now as I removed the master cylinder and power booster. They are already on their way back to the company for a refund.
     
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  21. HotRod33
    Joined: Oct 5, 2008
    Posts: 2,532

    HotRod33
    Member

    So have you been able to fix the problem
     
  22. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    No, just returning the items that were the possible problem. This is the second time I am sending back the booster and master cylinder. This problem started only after I replaced the original booster and master cylinder which was leaking. Now I have to get booster and master cylinder #3 and hope it does not lead to the same outcome.
     
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  23. David Gersic
    Joined: Feb 15, 2015
    Posts: 2,499

    David Gersic
    Member
    from DeKalb, IL

    Do you still have the original old parts?
     
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  24. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    Wish I did. This has been going on since late June. Once the first new booster and master cylinder were installed I discarded the original parts. The booster looked identical but the original master cylinder looked like a GM unit but the brake line outlets were on the other side of normal tword the frame rail, as the brake system is under the floor. Was not able to trace it down, but it was a 1 inch bore unit.
     
  25. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 2,598

    Elcohaulic

    You've learned the hard way, like most of us. Never throw old parts away. Drain and cover them up. Mark the box, year, engine and model...

    The single master cyl. can work, you need to have a good working emergency brake..
     
  26. bschwoeble
    Joined: Oct 20, 2008
    Posts: 775

    bschwoeble
    Member

    Conical seals. Can you explain or post picture?
     
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  27. David Gersic
    Joined: Feb 15, 2015
    Posts: 2,499

    David Gersic
    Member
    from DeKalb, IL

    Thats too bad. It might have been helpful to compare the details. Or possibly to just repair the m/c that was working for you.

    When the new ones show up, try breaking this system down and posting some pictures and measurements. Assuming you already bench bled the m/c and got the pedal, booster, and m/c installed…

    With just the m/c, plug both outlet ports. You should have essentially no pedal travel. There will be a little bit, as the slack in the linkages and pushrods is taken up. How much pedal movement do you get?

    I think you said you have pressure gauges. Put them on the m/c outlet ports. What are you reading there? Clearance may be tricky here.

    Plug the rear port, connect only the fronts. What’s the line pressure at the fronts? Solid pedal or not? How much pedal travel?

    If the fronts seem ok, now connect the rears. What’s the line pressure at the rears?

    Everyone has their own preference for bleeding brakes. I like the one-man check valve bleeders, augmented by sticking my phone in the wheel well and using its camera to view the fluid coming out until I’m good and sure that there are no more bubbles.
     
  28. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    From here on out nothing gets thrown away ,until the job is proven done.
     
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  29. 34Joe
    Joined: Nov 27, 2010
    Posts: 191

    34Joe
    Member

    Appreciate the info. I do not have any pressure gauges.
     
  30. Summit racing sells the brake pressure gauge sets (about $60.00). This may help quantify your troubleshooting efforts and explain the inability to lock up tires.
     
    Last edited: Nov 6, 2021
    bchctybob and brigrat like this.

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