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Thread: Flexible brake line replacement? (spongy even after bleeding brakes)

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    Flexible brake line replacement? (spongy even after bleeding brakes)

    After switching to Cleveland wheels, we initially had great stopping power, but now, even after carefully bleeding the brakes, they are spongy. I do not see any leaks, so I think it might be the original flexible brake lines... flexing. I was looking at replacing the lines, but they seem pretty expensive through Univair. Is there another source or maybe is it something that one could make?

    Any suggestions would be appreciated. Thanks!

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    skywagon8a's Avatar
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    Quote Originally Posted by DanP View Post
    After switching to Cleveland wheels, we initially had great stopping power, but now, even after carefully bleeding the brakes, they are spongy. I do not see any leaks, so I think it might be the original flexible brake lines... flexing. I was looking at replacing the lines, but they seem pretty expensive through Univair. Is there another source or maybe is it something that one could make?

    Any suggestions would be appreciated. Thanks!
    This indicates something other than the flexible lines since it was initially good.

    IF you also changed your master cylinder to one of the high pressure types, you should also change the flexible lines to a high pressure type.

    Check to be certain the brake cylinder slides smoothly on it's pins in the adapter plate. The bushings must be parallel. They also must be clean of any rust. Take off the inboard brake puck to check that the pins move smoothly in their bushings. If it doesn't this could give you the spongy feel. Some anti seize on the pins helps.
    N1PA
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    Eddie Foy's Avatar
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    Make custom lines cheaply.
    https://www.pegasusautoracing.com/gr...oupID=PTFEHOSE

    Quote Originally Posted by DanP View Post
    After switching to Cleveland wheels, we initially had great stopping power, but now, even after carefully bleeding the brakes, they are spongy. I do not see any leaks, so I think it might be the original flexible brake lines... flexing. I was looking at replacing the lines, but they seem pretty expensive through Univair. Is there another source or maybe is it something that one could make?

    Any suggestions would be appreciated. Thanks!
    "Put out my hand and touched the face of God!"

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    n40ff's Avatar
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    Can the flex lines degrade internally and cause issues like with some auto brakes? That's what sometimes causes Chevy front brakes to become problematic, locking-up etc. They develope a "flaper" inside which only allows fluid to easily go one dirrection.

    I remember my PA22 project years ago needed brake lines and the sticker shock I got from Univair. I made my own. As I recall they were not "AN" but rather 1930 vintage automotive, or something? Been a long time?

    Jack
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    Flex doesn't matter. Bulge does. See if your mechanic has a -3 or -4 mandrel and you can make Stratoflex hoses yourself. Or if approved doesn't matter go to a hydraulics shop and tell them you need brake lines made for a tractor.

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    55-PA18A's Avatar
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    Are both sides equally spongy?
    If original Scott master cylinders, maybe the diaphragms need replacing.
    New O-rings in brake pucks?

    Jim
    Last edited by 55-PA18A; 10-20-2020 at 08:51 AM.
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    Did you bleed the brakes from the bottom up or top down?

    Flex lines technically have a life limit of 5 years so should probably replace them anyway. The mandrels are not that expencive and you can buy them individually. Stratoflex has an assembly guide published which provides information on how to.
    Last edited by Scott 2020; 10-20-2020 at 08:28 AM.

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    The brakes were bled from the bottom up a few weeks ago and the diaphragms were replaced this summer. Original master cylinders, not high pressure. It is more the right side than the left, though the left is not great. I don't know if this helps, but after carefully bleeding a few weeks ago, I initially had passable pressure, but then it went spongy again. I looked around for leaks and don't see anything.

    One thing: if I push my hand on the rear heel brake, I reach a point where there is resistance, but if I apply more pressure, the resistance disappears and I can push right to the stops as if something in the system is giving way. That is why I was thinking there might be a bulge somewhere in the line.

    To Stewart's points: I was thinking about going through the whole system and doing a clean up. I will watch for those points. Thank you!

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    Have you had big temp changes lately, a closed system like the stock cub setup will expand and contract with temp.

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    https://www.summitracing.com/parts/aer-fcc0420 and associated ends. Field-assemble with no special tools, look way better than stratoflex, and easier to route/work with. Original equipment for all Wipaire Amphib hydraulic lines.

  11. #11
    www.SkupTech.com mike mcs repair's Avatar
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    Like skywagon said. Itís probably your pins on calipers binding or bent.


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    Do you pics of the brakes and lines? Are your bleeders pointing up or down? Any high spots in the lines?
    DENNY

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    Bleed them again.
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    To Denny's question, I haven't taken any picks yet of the lines. There is a slight low spot where the flexible hose goes into the belly of the fuselage. I bled them until fluid came out the top.

    The bleeders point down to the ground. I have a brake bleeder tool that I used.

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    Quote Originally Posted by jrb View Post
    Bleed them again.
    I was just going to say the same thing. Been there, done that a few times. Recently!

    What brake bleeder tool? I have an ATS pressure tank but with a properly set up brake system it's hard to beat a trigger pump oil can and a rubber hose for pushing fluid from the bottom. I need to invest in a vacuum bleeder. That looks like the way to go but I've never used one.
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    I also have the ATS pressure tank. Seems to work well for getting fluid in the lines. I've just got to figure out what else is going on, since it seems like the fluid is right to the top.

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    Bleeding brake lines has never been one and done for me. Bleed them. Hold pressure on brake. Bleed them. May have to do it again the next day. I donít have any special gizmo. Just add from the bottom. If I only had to bleed them 2 or 3 times that would be a win. Of course you could have other issues. But I always like to start with the simple low tech solution first. Bleed, bleed, bleed. Especially if you arenít finding leaks. Itís messy.
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    Gordon Misch's Avatar
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    With the Scott masters cylinders it can help to pump fluid from the wheel with the master ports closed, to take up any flex set into the masters' diaphragms. in other words, to pre-pressurize the system. Not so much as to interfere with wheel rotation though.
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    Gordon, I have not tried that. In terms of procedure, do you bleed them with the port open, and then pump in extra with the port closed?

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    skywagon8a's Avatar
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    DanP,
    Does the brake line enter the wheel cylinder at the top or bottom?
    Do you have parking brake valves?

    It might help if you drained and blew out the lines. Then start from scratch. Though in a Cub it should be a straight up hill run with no air traps.

    Use an oil pump can connected to the bleeder valve at the wheel with flexible (clear) tubing.
    Remove the filler cap on the master cylinder. Place rags around the master cylinder.
    Pump the oil can with someone watching the open master cylinder, until clear hydraulic fluid flows out of the filler hole. Alternatively, make an adapter connected to a clear hose to a tin can or jar. Pump til bubbles gone.

    Replace filler cap and close bleeder valve. How good are the brakes? Hard but low? Apply brake, set parking brake valve on, remove filler cap to top off master cylinder. Replace cap, release parking brake. How is it now? It should be better. Repeat as needed but don't over do it as you could lock the brakes.
    N1PA
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    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by skywagon8a View Post
    DanP,
    It might help if you drained and blew out the lines. Then start from scratch. Though in a Cub it should be a straight up hill run with no air traps.
    yes, this is a key step!

    If you ever observe the bubbles in a clear level/downhill(up?) tube, they will just nudge each other around and not get moved out of the system....

    this is about the only way i will mess with them if there's an issue... just start over with no bubbles....

  22. #22
    skywagon8a's Avatar
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    A bubble or a group of bubbles are able to let the hydraulic fluid bypass them with out moving. Sort of like foam forming in an eddy of a stream, swirling around while the water moves downstream. The surface tension of the bubble holds the bubble in place. Blow it out completely and there will be no bubbles.
    N1PA
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    PerryB's Avatar
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    Quote Originally Posted by Gordon Misch View Post
    With the Scott masters cylinders it can help to pump fluid from the wheel with the master ports closed, to take up any flex set into the masters' diaphragms. in other words, to pre-pressurize the system. Not so much as to interfere with wheel rotation though.
    Yes. Assuming air in the system is not the issue, precharging the system through the bleeder ports gives you a MUCH better pedal with the original masters.
    After Monday and Tuesday, even the calendar says WTF !

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    Flexible brake line replacement? (spongy even after bleeding brakes)

    I had a similar problem with my brakes after a new install. I removed the calipers and made sure the pucks were bottomed out. Pressed all the way in, then reinstalled and bled them again. Air can get trapped in the calipers even if you fill from the bottom, and it doesnít take much. That solved the problem for me.


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    Last edited by boarfish; 10-21-2020 at 01:26 AM. Reason: Used we on word.
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