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Leaking brake fitting

WingnutWick

Well Known Member
All, have a brake fitting that is leaking slowly but enough to put drips down overnight. I've tightened this as much as I dare, the only other option is to cut off the tip and re-do the flare (provided there is no other obvious cause causing a bad seal - like a piece of dirt etc). Is this correct thinking or should I try something else prior?

Thanks
 

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brake line fitting leak

Looks like leakage from the flared tubing to steel fitting interface.

You might already have a cracked flare or other damage to the aluminum tubing at this point. The "B" nuts on a 1/4" aluminum flared fitting like this one have a required torque range of 50-65 in-lbs (table 9-2 from AC43.13-1B). Higher torque is not better, it runs the risk of causing flare damage.

Open it up and check the flare to steel fitting interface for debris or damage. If nothing obvious is found (sometimes cracks are hard to find) you might just have to cut off the flare and re-do it.

Second thought: you can also try one of these - https://www.aircraftspruce.com/catalog/hapages/del37fittings.php?clickkey=2719162
I have no personal experience on how well they work....but might be worth a try. Although, even one of these might not seal a crack in the flare.
 
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leaking fittings

Look on ACS and look up Del-seals. Expensive fix, But, really cheap in the long run. They are an soft aluminum gasket sort of affair for flared connections. Some people use them on every fitting , Because they work so well.
They come in all the sizes you will need. Shipping is going to kill you, But that's life.
I've had leaks, used them and leak no more.
But if the line flare is cracked ain't nothing short of re-flare gonna fix it.
my three cents worth Art
 
Del seals are also made in copper, and seem to work better on steel AN fittings than the aluminum version.
 
Look on ACS and look up Del-seals. Expensive fix, But, really cheap in the long run. They are an soft aluminum gasket sort of affair for flared connections. Some people use them on every fitting , Because they work so well.
They come in all the sizes you will need. Shipping is going to kill you, But that's life.
I've had leaks, used them and leak no more.
But if the line flare is cracked ain't nothing short of re-flare gonna fix it.
my three cents worth Art

Unless you can confirm where it is leaking from, you could have a crack somewhere creating a compromised tube/flare. If that is the case, masking with a sealing device potentially sets you up for a more pronounced and unpleasant failure of the interface down the road. losing one brake on a strong X wind day is no fun with a castering nose wheel and down right scarry with a TD. A well formed flare should not leak and should not require any sealing devices or chemicals. Take the leak as a warning that something is not right and address it correctly.

I would cut the end off and re-flare it. I had one fail 5 hours into phase I. Just luck it was a calm day. Clearly something was compromised in the flare, but had no visual cues that it was bad prior to the failure.

Larry
 
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If you have fluid coming from the aft end of the nut, the sealing surface is compromised. Either a bad flare, cracked flare, or like the pic, a really damaged steel adapter fitting. YES, believe it or not, client called and said our hose was leaking. Naaa---take it apart and take a pic of the adapter==OOPS----. This was installed by an A&P.

So take things apart, and INSPECT them. Dont guess.

Tom
 

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This is a long shot, but check the flare angle is correct. Aviation and automotive use different angles. As others have said, ovrr-tightening is not the solution. Open it up and look. Yes, you’ll need to catch the fluid as it comes off or have a big mess.
 
Check B nut and sleeve

I would also check the B nut and sleeve, the gap between the B nut and sleeve looks too big for an aircraft standard part
 
The Del-seal thingys.
Used a couple as needed during the phase 1.
No problems after 500+ hours.
 
Del seals work well, but are not a substitute for good workmanship, or poor tools.
+1
The alternate methods suggested may be better but personally I would just fix it using standard methods. As suggested, it could be a crack or bad AN fitting or both. Or maybe someone flared using an automotive flare tool (wrong angle). Fix that and fly on.
 
Thanks for all the feedback folks. Looked at the flare and fitting and they look decent, though the flare has a slight imperfection in the edge which may be the cause. Tom - I still have some lines from you that I may give another shot at. If you remember - a couple years ago, I couldn't get them to not squeal. In hindsight, I am thinking that I had some air in there that may have been causing it.
 
Just out of curiosity...why do you have a steel AN fitting on there? The tube is aluminum, the brake housing is aluminum. Pretty sure an aluminum AN fitting is appropriate there...
 
Just out of curiosity...why do you have a steel AN fitting on there? The tube is aluminum, the brake housing is aluminum. Pretty sure an aluminum AN fitting is appropriate there...

Good question: not my plane and I don’t know the full history there.
Stupid question: Does it matter?
 
Good question: not my plane and I don’t know the full history there.
Stupid question: Does it matter?

For one thing, the torque values are vastly different for aluminum vs. steel fittings. And, although inconsequential for a single fitting or two, weight...if this was done all over a large airplane, I guess, it could add up. Finally, IMO, it's overkill...you use steel fittings where high heat could be a problem (FWF passthroughs, in case of fire; oil cooler fittings; etc.).

Putting a steel fitting into an aluminum boss might, I dunno, also be a problem when tightening it to the needed orientation. Others can weigh in here. I'm a systems engineer, not an ME :). We work to requirements, and anything more is unnecessary, more complicated, more expensive, heavier, etc. LOL!
 
For one thing, the torque values are vastly different for aluminum vs. steel fittings. And, although inconsequential for a single fitting or two, weight...if this was done all over a large airplane, I guess, it could add up. Finally, IMO, it's overkill...you use steel fittings where high heat could be a problem (FWF passthroughs, in case of fire; oil cooler fittings; etc.).

Putting a steel fitting into an aluminum boss might, I dunno, also be a problem when tightening it to the needed orientation. Others can weigh in here. I'm a systems engineer, not an ME :). We work to requirements, and anything more is unnecessary, more complicated, more expensive, heavier, etc. LOL!

If one component is aluminum, the aluminum torque spec should be used, I believe. No issue with a steel fitting installed with an aluminum tube and nut. Certainly not necessary here, but no issue in doing so. One key advantage is that steel NPT fittings installed into an aluminum FNPT have a much lower chance of galling the alum threads than using both aluminum FNPT & aluminum MNPT. This is the primary reason they are used on oil coolers. The cooler is aluminum, so no point in having a fitting that can stand more heat than the cooler or the hose can. (weakest link philosophy) Some also believe that the steel fitting can handle more stress from the hose constantly moving and therefore less chance of fitting failure in that application - fixed cooler with moving engine. I tend to use only steel fittings FWF for these reasons. In those cases the hose ends are typically aluminum. Steel can handle a LOT more fatigue cycling from vibration than aluminum can and it is usually the fitting that gets the stress as opposed to the hose end.
 
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