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Technical Brake Bleeding!?

Discussion in 'The Hokey Ass Message Board' started by jaw22w, Jan 2, 2022.

  1. It is odd for sure. Ground profile is related spring adjustment so you wouldn't think that angle would play into air movement with the fluid but it can and does at times. It's seems to be with a big Rubber Rake I find it showing up. Even with that 3" is about all the difference we are talking about. It seems hardly possible that little step could cause a problem, but it can. Odd as it is it don't cause an issue on all those jobs all the time. I have no idea what brings on these things. Probably why it is such a problem when it shows up. Really glad you got it sorted out, now you gotta retrain that right foot.
     
  2. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,464

    jaw22w
    Member
    from Indiana

    Yeah, last night I got curious about the heights of the various components in my brake system. I had never really paid any attention to it. So I had the car on the lift and took some measurements at ride height. The MC outlets are at 15" off the ground. The front caliper bleeders are at 14". The rear caliper bleeders are at 16". Just 1" above or below the MC to the calipers. Lines all run parallel to the frame. No humps or bumps. The only hump in the lines at all is over the center section of the rear end. I just couldn't imagine where air could be trapped. If I hadn't seen it I wouldn't have believed it. The air was trapped in the right front.
    Edit: I think every time I bleed brakes again on anything I am going to jack up the front and passenger sides, just as a matter of course!
     
    Last edited: Jan 13, 2022
  3. Most often Facts are stranger than Fiction. I'd like to know how fluid bypasses air in a 3/16 id line.
     
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  4. brigrat
    Joined: Nov 9, 2007
    Posts: 5,496

    brigrat
    Member
    from Wa.St.

    On some models the M/C was mounted in a drastic nose high position from the factory..............
     
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  5. gimpyshotrods
    Joined: May 20, 2009
    Posts: 19,919

    gimpyshotrods
    ALLIANCE MEMBER

    This is why I do the "bleed bottle on step ladder thing".

    Irrespective of how to the system is built, it creates a temporary highest point in the system.
     
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  6. gimpyshotrods
    Joined: May 20, 2009
    Posts: 19,919

    gimpyshotrods
    ALLIANCE MEMBER

    A bunch of GM stuff was like that, to kick the body of the master cylinder over other components. This was to minimize the area that the engine compartment occupied on the platform. Small car, big interior.
     
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  7. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,464

    jaw22w
    Member
    from Indiana

    That method is the one I was using. Caliper above the MC and bottle above that. It would not get the air out until I jacked up the front of the car.
     
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  8. gimpyshotrods
    Joined: May 20, 2009
    Posts: 19,919

    gimpyshotrods
    ALLIANCE MEMBER

    Whatever it takes! Just happy it is done!
     
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  9. Doublepumper
    Joined: Jun 26, 2016
    Posts: 1,141

    Doublepumper
    Member
    from WA-OR, USA

    Strange, some systems are just more difficult to bleed than others. Years ago I rebuilt the brake system on a '59 Chevy and couldn't get it completely bled. I struggled with that thing using everything at my disposal, including a vacuum pump. I ended up taking the car to a guy with a pressure bleeder setup and got it done, no problem Since then, I've always considered pressure bleeding to be the best method of positively removing all the trapped air.
    Curious to know if it would have worked here...might avoid having to jack up he car.
     
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  10. alchemy
    Joined: Sep 27, 2002
    Posts: 17,914

    alchemy
    Member

    Me too. How does a bubble in 3/16" line stay at the high point in that loop, but the fluid goes around it? I just can't see it happening. And tilting the car a few degrees was enough to magically fix it?
     
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  11. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,464

    jaw22w
    Member
    from Indiana

    I am certainly no engineer. and I can't tell you the science behind it, but I can tell you anecdotally, that it happened to me... TWICE!
     
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  12. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,464

    jaw22w
    Member
    from Indiana

    Thinking about this some more. Maybe the air is not in one big bubble blocking the line. I can see a small string of bubbles laying along the top of the line, not blocking the line, and fluid passing under the bubbles. I think this is a lot more likely than 1 big bubble. When I was bleeding, I did notice that I wasn't getting a lot of air all at once, but I was getting streams of small bubbles. Maybe that means something. Maybe not.
     
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  13. Happydaze
    Joined: Aug 21, 2009
    Posts: 1,279

    Happydaze
    ALLIANCE MEMBER

    Highly unlikely that this is the answer. Theoretically I reckon capillary action (attraction? Been a long time since school!) will keep the fluid across the diameter of the tube. From practical experience I've watched it in the clear bleeding tube (of approx 3/16 diameter, possibly greater) and that is just what the fluid does. And with the bleed tube blocked the air bubbles dont rise in the tube either. Clever stuff that brake fluid. Vickwithahemi has been strangely absent in this thread!

    Chris
     
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  14. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,464

    jaw22w
    Member
    from Indiana

    Hell, I'm just taking wild assed guesses here. All I know is I drove that car with 2 pump brakes almost 7 years and 25000 miles after bleeding it nose down every time. A lot of times. Then when I bled it nose up, all of a sudden, I have 1 pump brakes.
    Obviously, there is an explanation. I just don't know what it is, but I've got good brakes now.
     
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  15. Boneyard51
    Joined: Dec 10, 2017
    Posts: 5,573

    Boneyard51
    Member

    Actually that is quite accurate! Back many posts back, I mentioned how air bubbles can “ shoot” through a brake system if it has air and pressure. It’s been too many moons for me to even remember where I saw it , now. But I do remember seeing minute air bubbles in the top of the brake lines , not huge ones, shooting through the clear brake lines on that mock up brake system. Don’t remember much other about that class, but the little bubbles shooting through the system, were imbedded in my mind!
    That is why I never “ build a pedal” bleeding brakes. Just a push of the brake pedal with the valve open.





    Bones
     
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  16. Budget36
    Joined: Nov 29, 2014
    Posts: 8,412

    Budget36
    ALLIANCE MEMBER

    Good deal!

    Is the MC down in front with your rake?
     
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  17. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,464

    jaw22w
    Member
    from Indiana

    That's what I see in my mind.
     
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  18. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,464

    jaw22w
    Member
    from Indiana

    At ride height the MC is 0.00 degrees level, and the frame is 2.50 degrees down in front on my digital angle cube.
     
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  19. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,464

    jaw22w
    Member
    from Indiana

    Too bad we can't see inside those lines. We need SUPERMAN!
    Or maybe Dale Earnhardt. They said he could see the air!
     
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  20. indyjps
    Joined: Feb 21, 2007
    Posts: 4,839

    indyjps
    Member

    Happy you found it.

    I'll share some OT if it helps, brake related and may apply. Swapped to stainless brake lines on daily driver 06 silverad0. Lot of concern on making sure the abs valve was fully fed with fluid as the system was filled. Gravity fed overnight to the abs valve, old master cylinder cap and hung the tank from the hood latch. Then switched to pressure bleed with same master cylinder cap and a small pressure garden sprayer. While the pressure was on, crawled around under the truck tapped on all the lines to a corner. Cracked the bleeder. Went around the truck twice. May have been overkill. But those valves are expensive and difficult to swap.
    I've also started doing a final brake bleed
    with the engine running to ensure any power brake, abs, or controls are running. This solved a soft pedal on one of my wife's drivers years ago, and I've kept doing it.
    I never force caliper pistons back under pressure when changing brakes, crack the bleeder when compressing the piston.
     
  21. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,996

    jimmy six
    ALLIANCE MEMBER

    I have always pushed back the piston when replacing front pads as the second step in a front pad replacement. The first step is to take off the MC lid to make sure additional fluid has not been added. If it’s full I suck some out and use a flat screw drive to press back the piston with the old pad. I don’t know if that meets your definition of under pressure or not.
     
  22. indyjps
    Joined: Feb 21, 2007
    Posts: 4,839

    indyjps
    Member

    Older stuff - It's only a few minutes difference to crack the bleeder and back off the piston, I do it on old stuff to flush fresh fluid thru the caliper at brake pad change anyway. I doubt the fluid in the caliper exchanges readily with any new fluid in the reservoir, the fluid that hangs in the caliper sees all the heat cycles. I see a benefit to flush it.
    Late model stuff, I don't want to take a chance of damaging abs related BS.

    Just sharing info and perspective. Not trying to convince anyone to do it the way I do.
     
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  23. garyf
    Joined: Aug 11, 2006
    Posts: 249

    garyf
    Member

    I agree with your way. Forcing the nasty brake fluid from the brake calipers back into an ABS system can be very expensive.
     
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  24. You have to bleed them off the car with the hoses still attached and the rotor and caliper down flat on the ground, and bleed all the bleed valves.
     
  25. OK. I had that same 2-pump problem with my Willys for years. I bled, and bled, and bled, no change. My system is really a cludged up mess with '68 manual GTX master cylinder, '70s Ford Torino front disk brakes and '56 Olds/Buick finned drum rear brakes. Add to that a vintage '50s GM Bendix remote vacuum booster.

    I finally got desperate and ignored the usual recommendation to adjust the master cylinder push rod to allow the piston to totally relax. I turned the pushrod in to preload the piston and VOILA, I got rock solid brakes. Try turning your push rod in and preloading your master cylinder. Worst that can happen is you lock up your brakes and you won't go anywhere until you back it off.
     
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