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Old 01-26-2021, 11:53 AM
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jcarne jcarne is offline
Join Date: Jul 2016
Location: Worland, Wyoming
Posts: 1,505
Default Weird brake leak, what would you do?

As you can see in the picture I attached I went out to the hangar a few weeks ago and notices a slight brake leak. There was a small amount of fluid on the ground and a hanging drop on the right caliper. I pushed on the pedals and there is still good pressure on both sides and the pressure did not cause any more drops of fluid.

The weird part is that the aircraft has not moved, has always been in a heated hangar at 42 degrees. To top it all off I haven't noticed any more drips in about the last two weeks. The brakes were also never actuated to cause this. Long story short I'm kind of puzzled. I would think if the there was a problem with the o-ring on the piston it wouldn't just stop like this. Thoughts?
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Old 01-26-2021, 12:05 PM
Kyle Boatright Kyle Boatright is offline
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,365

I had a situation like that several years ago. I assumed a seal got hot and leaked, then returned to shape when it cooled. Surprisingly, it never leaked again. Almost certainly a dumb move on my part not to pull the piston and replace the seal at that point, but I got away with it.

I have since replaced the o-rings with spiffy viton rings.
Kyle Boatright
Marietta, GA
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2019(?) RV-10
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Old 01-26-2021, 01:25 PM
74-07 74-07 is offline
Join Date: Dec 2016
Location: Greenville, SC
Posts: 543


I just had exactly the same on my left brake. Pulled wheel pant and the bleed screw AND the bottom caliper bolt have obviously been attracting dirt and were very slightly damp. Cleaned it all up, placed a paper towel underneath it and pumped like crazy and held pressure on it for what seemed to be an eternity. Nothing. I rebuilt both calipers and flushed the system about a year ago. I did use viton o rings. Guess I'm going to pull the left caliper and look at it real close and then rebuild it one more time.
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Old 01-26-2021, 01:30 PM
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jcarne jcarne is offline
Join Date: Jul 2016
Location: Worland, Wyoming
Posts: 1,505

Thanks for replies so far guys. I should also add that these brakes are brand spanking new and have never even been run before. They have however been holding fluid in them for more than 6 months before this happened. Therefore, I don't think heat has anything to do with it.

Unfortunately, I will be flying in some seriously cold weather so it sounds like the vitons may not be the best choice for me.
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Old 01-26-2021, 03:54 PM
Paul 5r4 Paul 5r4 is offline
Join Date: Oct 2006
Location: Foley, Al
Posts: 595

If they are new then perhaps a small amount of brake fluid got onto the caliper during assembly and eventually ran down to the point where enough collected and dripped a time or two. I would clean it up and put a paper towel down and keep watch. No more dripping, brake fluid level check and good pressure... I'd say you're good to go.

Edited: IFFFF there continues to be a small drip even only occasionally, I'd break it down and replace the o-ring in the caliper. I always did worry about landing and being heavy on the brakes and with a sudden gush, one goes out. The possibility of loss of control increases. It's actually part of my prelanding checklist. Brake check equal/normal feeling pressures.
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Last edited by Paul 5r4 : 01-26-2021 at 04:01 PM.
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Old 01-26-2021, 04:04 PM
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wcalvert wcalvert is offline
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Gear down, flaps full, hook down, harness locked, brakes checked, fuel...
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Old 01-26-2021, 04:51 PM
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Vlad Vlad is offline
Join Date: Oct 2008
Location: Utah
Posts: 8,275

Any chance a small amount sprayed/lost fluid during the bleed collected then dripped down? I also had a hairline circumference crack due to overflaring aluminum brake line above the caliper. Noticed a tiny almost dried out trace then investigated further.
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Old 01-26-2021, 10:25 PM
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bhester bhester is offline
Join Date: Jan 2005
Location: Hopkinsville, KY
Posts: 991
Exclamation Make sure it goes back in correctly

If you take the puck out to change to o-ring just make sure it goes back in correctly. It can be put in wrong and you’ll loose your brake when you least expect it. This is the correct way. If it is put back wrong the o-ring will be too close to the edge and will come out when you apply the brakes.

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Old 01-27-2021, 05:35 AM
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rzbill rzbill is offline
Join Date: Nov 2005
Location: Asheville, NC
Posts: 2,717

Actions regarding this leak depends on the owners tolerance for being stranded at an outlying airport or worse, stranded in a ditch.

I had a winter leak of left brake a couple of years ago. Fluid on the ramp when i walked up to the bird. Fortunately, I had a spare car there and I was able to drive home in 3 hrs which was a normal thing for crappy weather commutes. I had all the tools i needed in my emergency kit but no fluid to replenish. Fixed it on the ramp the following week.
Being further afield with no wheels would have been a pita.

So... o-rings are cheap so they are getting changed at annual now dispite it being a nasty job. It's better done at the cozy hangar at home airport.
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Old 01-27-2021, 08:34 AM
Feetwet Feetwet is offline
Join Date: Mar 2008
Location: Seattle/Tucson
Posts: 60
Default nicked the piston

I had a similar problem with a continuous seep from my left brake. I had previously replaced the piston O-ring. It was just a seep and would go for 2 or 3 flights before it appeared again. Checked the connections and the bleed screw, all fine. Eventually pulled the slave cylinder and pulled out the piston with O-ring. There was a very slight scoring in the slot that the O-ring fits into. Some hack mechanic (me) had used a small screwdriver to reach down the side of the slot to pry out the O-ring, and in the process must have slightly scored the groove - it was quite tiny. Ordered new piston (~$100), put in new Viton O-ring (make sure it is brown) and the seep went away. Do make sure the piston is installed in the correct direction, new pistons actually have printing that says "this side out".
I always have trouble getting that ring out of the groove. I have resolved in the future to use a fishhook to stab the O-ring in the middle and pull it out that way.
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