Periodic air in brake line

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GRTfast
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Periodic air in brake line

Post by GRTfast » Tue Nov 07, 2017 9:12 am

Every 2-3 months, my brake pedal begins to feel a little soft. When I say a little soft, I mean it travels maybe a 1/2" further than normal, and is just spongy enough to be detectable. I will then go around the car and bleed each caliper with my vacuum bleeder (starting with back right, then back left, front right, then front left), there is always a little air bubble coming from the right front caliper. This bubble is maybe a half inch long in the rubber bleeder tube. The system is plumbed with Russell brake lines with -3 an connections. I'm using a single Wilwood master cylinder for the entire system. Everywhere there is a tee, it is an Earl's brass tee with female 3/16-24 inverted flair connections, that I have male/male adapters screwed into in order to mate up to my -an lines.

I replaced the front calipers and this had no effect. Also, there is never any fluid leaking from the system anywhere. I even put pressure on the pedal with a wooden dowel and left it overnight, and it held pressure with no leaks.

The time that it takes for the air bubble to show up in my vacuum bleeder tube suggests that the bubble is at the tee where the line for my right caliper connects. That tee has the incoming line from the left caliper tee, the line out line to the right caliper, and the brake light pressure switch.

question:

1. Is it possible for there to be a leak so small that it somehow lets air in, but doesn't let fluid out, even when the fluid is routinely under fairly high pressure?

I have attached a sketch of my system configuration
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Brake schematic.JPG

Jeff Lee
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Re: Periodic air in brake line

Post by Jeff Lee » Fri Nov 10, 2017 11:37 pm

Do your calipers have bleed screws at the top? Do you have a brake pressure stage gauge? I recently spent at least an hour bleeding my 4wdb’s (MW calipers with both top and bottom bleed screws). Using the top bleed screw, finally no air in the system. But still spongy brake. Then I had a “duh” moment and remembered to bleed the gauge; which is the highest point in my system. Made a huge difference. On a 1-10 scale, I’ll give it a 7 right now. Next I’m making sure the calipers are spaced as required from the mounting surface which has instructions on the MW site. I’m also replacing the o-rings as they are at least 10 years old and replacing all fluid. There are many good ideas here:

http://www.markwilliams.com/braketech.aspx

And I just read this a few posts down that may resolve your issues. See thread engagement:

viewtopic.php?f=11&t=51270
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GRTfast
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Re: Periodic air in brake line

Post by GRTfast » Sat Nov 11, 2017 5:58 pm

Thanks, that’s all good stuff. My issue is, I bleed it and get a rock solid pedal that lasts for a month or more. Ever so slowly it gets a little spongy. I bleed it and find air at the right front caliper.

All my bleed screws are on top of the calipers.

The part that is so weird to me is that I’ve checked every joint and there is absolutely no fluid leaking, yet I seem to leak a tiny bit of air into the system. I’ve tried new calipers and new fluid. Makes no difference. Prolly gonna start replacing lines next.

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Re: Periodic air in brake line

Post by amcenthusiast » Sat Nov 11, 2017 8:39 pm

Seems like a case for 'The Amazing Kreskin' without seeing the system firsthand?

Could it be heat related, where fluid in the line 'boils'?

Would LMA brake fluid help or conversion to silicone brake fluid do the trick? -more guesses

Hopefully this article on brake fluid is not too simple minded for your sophisticated brake system:

https://www.hemmings.com/blog/2013/12/0 ... -you-care/
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GRTfast
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Re: Periodic air in brake line

Post by GRTfast » Sat Nov 11, 2017 10:33 pm

amcenthusiast wrote:
Sat Nov 11, 2017 8:39 pm
Seems like a case for 'The Amazing Kreskin' without seeing the system firsthand?

Could it be heat related, where fluid in the line 'boils'?

Would LMA brake fluid help or conversion to silicone brake fluid do the trick? -more guesses

Hopefully this article on brake fluid is not too simple minded for your sophisticated brake system:

https://www.hemmings.com/blog/2013/12/0 ... -you-care/
More good stuff.

My brakes don’t get used very intensely. It’s a cruiser street rod. Nothing is dragging, I’ve already checked all the calipers for excessive heat. Boiling fluid is highly unlikely.

I’m convinced I have air leaking into the system somehow. I just have to figure out how/where.

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Re: Periodic air in brake line

Post by fdicrasto » Sat Nov 11, 2017 10:37 pm

Is the master cylinder located above the rest of the brake system as is the norm except for a lot of race cars apps. ?

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Re: Periodic air in brake line

Post by GRTfast » Sat Nov 11, 2017 11:10 pm

fdicrasto wrote:
Sat Nov 11, 2017 10:37 pm
Is the master cylinder located above the rest of the brake system as is the norm except for a lot of race cars apps. ?
It’s a little below them. I tried an anti-bleedback valve to see if the issue was the fluid gravity feeding back to the master and pulling the pads back, and it made no difference.

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Re: Periodic air in brake line

Post by Geoff2 » Sun Nov 12, 2017 4:09 am

Air in the right front caliper? Replace the seal &/or seal.

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Re: Periodic air in brake line

Post by GRTfast » Sun Nov 12, 2017 7:25 am

I did one better... I replaced the caliper. No change. I guess maybe i got two defective seals in a row, but that seems highly unlikely. I’m leaning towards a leak in one of the -an brake lines or fittings. It’s just weird to me that no fluid leaks out.

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Re: Periodic air in brake line

Post by geraldtson » Tue Nov 14, 2017 7:57 pm

Not sure if this will help but doesn't cost much you might try installing a 2 psi residual valve on front brake lines if your master cylinder is below calipers. Jegs has them for around 20.00 bucks each.If you try it order an extra one in case you pull any threads and check for any adapters you may need.

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Re: Periodic air in brake line

Post by GRTfast » Wed Nov 15, 2017 8:19 am

geraldtson wrote:
Tue Nov 14, 2017 7:57 pm
Not sure if this will help but doesn't cost much you might try installing a 2 psi residual valve on front brake lines if your master cylinder is below calipers. Jegs has them for around 20.00 bucks each.If you try it order an extra one in case you pull any threads and check for any adapters you may need.
I have one. I tried it because i thought I was getting fluid gravity feeding back to the master, causing the pads to pull away from the disks. Turns out that wasn’t the issue. Thanks for the suggestion.

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Re: Periodic air in brake line

Post by ijames » Wed Nov 15, 2017 10:37 am

The only unique thing I see about the right front is that that is where the brake light switch is located, and your "bubble flow timing test" indicates that that is where the bubble forms. So, that's where I'd go next. Maybe you are getting a bit of electrolysis between the switch body and your tee. Can you try a different brand of switch? Any difference in materials at that tee, compared to the other wheels?

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Re: Periodic air in brake line

Post by GRTfast » Wed Nov 15, 2017 5:00 pm

ijames wrote:
Wed Nov 15, 2017 10:37 am
The only unique thing I see about the right front is that that is where the brake light switch is located, and your "bubble flow timing test" indicates that that is where the bubble forms. So, that's where I'd go next. Maybe you are getting a bit of electrolysis between the switch body and your tee. Can you try a different brand of switch? Any difference in materials at that tee, compared to the other wheels?
That’s a great thought. I’ll look into it. All the tees are brass, and all my adapters, and the switch are steel, but not sure if they’re the same steel. Good thinking.

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