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My brake line elbows are leaking on my Grove aluminum gear legs - Options?

So, to tap a NPT thread, would that require a particular tap or a standard one is good to go ??

A particular tap. NPT stands for National Pipe Tapered threads. The hole and threads are slightly conical to grab the fitting as it tightens. Standard taps are straight.
 
Success!

Research and consultation continued yesterday. After comparing different sealants I reached a similar conclusion to many here and ordered Loctite 547 pipe thread sealant for its superior pressure retention properties. I conferred with a local machinist at St. Pierre Inc. regarding modifying 1/8" NPT tap or using modified plugs as thread chasers. 1/8" NPT galvanized steel plugs were purchased. Checked NPT thread gauge: 27 tpi. Checked clearance in gear pocket: 1.5". Checked depth of tightened galvanized plug in existing tapped holes: 1/8". Checked max depth of tapped fitting hole: 1-5/16".
This morning I went over to St. Pierre Inc. machine shop, laid out photos of what I was working with and what I needed, and they modified my tap while I watched and took photos. They squared off the middle shank to fit a 5/16" open end wrench and cut off the excess so it would fit into my confined space. They only charged me $20 for the mod and said I could pay them when they finished some baggage door prop pins they're also making for me. I was thrilled!
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I lubricated the tap with cutting oil, inserted it into the right gear leg fitting hole and carefully began clearing and extending the threads. This is the first time I've cut or chased NPT threads and as I did so, I felt the tap bind up somewhat, then turn a little easier, then bind up a little more and get easier etc. It made me wonder if Grove's original tap didn't go into the drilled hole straight... maybe that was part of the problem. I was doing all this very carefully, backing off frequently to clear the tap, and was eventually satisfied with the increased depth I had achieved.
(The tap appears dark in this photo because it's in the shade of the ruler in relation to the flash angle)
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When I was done I cleaned out the entire gear leg brake fluid passage by gently blowing air into the bottom fitting (not through the caliper!) and having a vacuum nozzle at the top to catch debris. I followed that by thoroughly cleaning the new threads with a double-folded pipe cleaner bent to a right angle and wetted with isopropyl alcohol. The increased depth was checked with a plug and the threads cleaned once more before the gear pocket was covered to keep out any debris generated while I trimmed the pocket opening on the left side, deformed the inner floor skin and removed the left elbow fitting. I followed the same procedure on the left; cutting, cleaning and checking. After reviewing the Loctite 567 TDS I carefully applied it to each new fitting in turn; torqued and clocked; excess sealant wiped off. The detached brake line fittings were reconnected and all fittings torqued and sealed.
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So everything is back together and ready, but I will give the sealant 24+ hours cure time before refilling and testing. I'm feeling good about this; keep your fingers crossed.
(Dan Horton, I gotta ask... what do you think? Did I do ok here?)
 
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Marty - quick question, why is your brake line outside like that? Do you have a photo from a bit further back? That's different from mine which comes out of the gear leg and then goes up into the cockpit.

20050328221707113_4.jpg
 
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Some guys run the hard lines under the gear leg, then up the other side. I think that makes it a little easier to work with the hard lines.

Marty - quick question, why is your brake line outside like that? Do you have a photo from a bit further back? That's different from mine which comes out of the gear leg and then goes up into the cockpit.

20050328221707113_4.jpg
 

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Mo----maybe its the picture angle, but it appears to me that there is still alot of exposed thread on the NPT side, as compared to what I normally do. How tight is the fitting?
An can you post a pic of the rigid tube? Just curious.

Tom
 
Mo----maybe its the picture angle, but it appears to me that there is still alot of exposed thread on the NPT side, as compared to what I normally do. How tight is the fitting?
An can you post a pic of the rigid tube? Just curious.

Tom

It's tight enough to not leak, with PTFE, which is all you need. I'm not sure I understand this counting the threads thing.

Photo of the rigid line setup is in the post above. I used flexible braided stainless as shown in my photo a few posts up, as I'm not a fan of rigid lines anywhere where there's a lot of vibration and the stuff just isn't serviceable.

Not trying to get into a PP contest with anyone else here, but I've been installing and maintaining brake systems on race cars for about 10 years now, where a brake failure is akin to an engine failure in an aircraft. Never had a single problem... https://youtu.be/a_v8aZUsUv8?t=435
 
(Dan Horton, I gotta ask... what do you think? Did I do ok here?)

Martin, if it works, it's golden ;)

Serious answer? Shop 101...turning a tap with a wrench is always risky. Quick sketch below. Length L is the length of the tap protruding from the workpiece. Applying a force to the handle results in a tipping moment. The tap doesn't go straight into the hole, and the outermost threads tend to be sloppy.

That's why we use a T-handle. Equal force on two handles at the same time means no moment, just torque.

So, not a good practice, but if it works here, a win is a win!
.
 

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Martin, if it works, it's golden ;)

Serious answer? Shop 101...turning a tap with a wrench is always risky. Quick sketch below. Length L is the length of the tap protruding from the workpiece. Applying a force to the handle results in a tipping moment. The tap doesn't go straight into the hole, and the outermost threads tend to be sloppy.

That's why we use a T-handle. Equal force on two handles at the same time means no moment, just torque.

So, not a good practice, but if it works here, a win is a win!
.

Concepts known and understood; risk taken with full awareness. Glad you expounded on it for the benefit of others. For me, removing the gear was a larger overall risk. Not sure whether I'll test it tomorrow or after I return from transition training with Bruce Bohannon next week. I'll keep all posted.
 
Marty - quick question, why is your brake line outside like that? Do you have a photo from a bit further back? That's different from mine which comes out of the gear leg and then goes up into the cockpit.

20050328221707113_4.jpg

It really isn't outside; it's routed around the gear bracket then into the gear tower. This was done a long time ago; I don't remember why I routed it this way. I'm thinking it had to do with obstacles in the tower or maybe that's where the factory provided the hole.
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It really isn't outside; it's routed around the gear bracket then into the gear tower. This was done a long time ago; I don't remember why I routed it this way. I'm thinking it had to do with obstacles in the tower or maybe that's where the factory provided the hole.
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I used a similar approach when I plumbed my legs 10 years or so ago and documented it here:

https://vansairforce.net/community/showpost.php?p=1117862&postcount=1

My reasoning was to be able to use the stock bulkhead fitting locations in the fuselage.

Skylor
 
Spring 2007, during fabrication.
 

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Aeroshell sealant compatibility chart

I received a response from Hiew Nguyen, Aeroshell Regional Technical Manager for North/South America. I will include the full correspondence including the chart he supplied. The disclaimer at the top of the chart was truncated but the most important sentence remains: these are only guidelines. I will also stress that Aeroshell does NOT recommend sealants; i.e. they do not wish to expose themselves to any liability for the information provided.

Hello, Martin – I received your inquiry below:

I'm using Aeroshell Fluid 31 in my aircraft brake system. This is the first time the aircraft brake system has been filled and I'm experiencing leaks at threaded plumbing joints (1/8" NPT aluminum AN fittings in aluminum gear legs) that were sealed using Permatex #2 non-hardening sealant on the threads as recommended by the manufacturer. It appears that the Fluid 31 may be breaking down the sealant. What pipe sealant would you recommend for this application?

We do not recommend sealants, but I can recommend a compatibility chart below. AeroShell Fluid 31 is a synthetic hydrocarbon oil approved to MIL-PRF-83282D, so it should have general compatibilities with the known elastomers/plastics in the chart below. As the aviation application would call for this spec in the hydraulic brake system, if I’m not mistaken, all other fluids approved to MIL-PRF-83282D are also synthetic hydrocarbon. They would all have similar response to the sealant. I would consult the airframe or brake OEM to determine a compatible sealant for the MIL spec hydraulic fluid, or a sealant manufacture can provide if they would be compatible with synthetic hydrocarbon fluid.
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Since Loctite is a methacrylate ester and its primary function is thread sealing, it appears to be a good choice for use with both mineral and synthetic hydrocarbon fluids produced by Aeroshell. The Permatex #2 TDS does not proclaim its chemical makeup, so no determination can be made on that basis. Somewhat of a flawed TDS, in my opinion. I find it interesting that according to Aeroshell TDS documents, Fluid 41 and 31 are compatible despite one being a mineral based (some charts say petroleum based) fluid and the other being synthetic hydrocarbon based fluid... not that I truly understand the difference. I'm way out of my depth here... but still wish to understand at least some of it. My motto below has never been more appropriate...
Your results may vary. Please don't blame me, Hieu, Aeroshell, Loctite or Permatex.
 
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Practically any common sealant, including Permatex #2, will be fine given good threads and enough thread engagement.

I've attached a scan from a classic reference, Machinery's Handbook. Take a look at the "Pitch of Thread" and "Handtight Engagement" figures for the 1/8 and 1/4 NPT threads found in most of our RV applications.

1/8 NPT: 0.1615"/0.03704" = 4.36 threads engaged
1/4 NPT: 0.2278"/0.05556" = 4.1 threads engaged

Note this engagement is hand tight, the point where the diameter of the male and female threads is essentially the same. It does not include subsequent tightening, when the threads are placed under load.
.
 

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Thanks Dan

Thanks Dan, I believe this explains it all.
I recently noticed a slight weeping from one lower Grove caliper fitting despite re-sealling with 567.
Not saying that the Grove machined NPT ports are systematically guilty but I will re-tap the culprit, and make sure proper thread engagement as per the above document.
And I'll also check the other (non-leaking for now) fittings for the same engagement.
I recall that only a few threads were engaged by hand before having to use a wrench. I suspect not deep enough taping from the start...
 
Obviously many installations don't have all the thread engagement described in the table, and yet they still seal up and give good service.

Opinion, no proof, but I suspect many hand cut female threads don't match the specified thread form near the top of the hole, making depth of engagement more important.
 
My turn

Looks like it's my turn now. I filled my brake system today and both sides are leaking from the fitting at the top of the grove gear.

I'm planning to remove the gear legs and run a tap in the threads. Fortunately, I installed the bolt head clips that allow the bolts to be installed with the nuts on the bottom so removing-replacing the legs shouldn’t be too difficult.
 

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Another Fail, with Video

After giving the refit a 12 day cure time, I refilled my brake system and checked again. The left side is solid. The right side is worse than I thought.
See Video:
https://youtu.be/_vTm7Bqe2Jo
Pretty disgusted. Don't really want to hear any more opinions at the moment, but I am sharing this before going back to work the problem.
:mad:
 
After giving the refit a 12 day cure time, I refilled my brake system and checked again. The left side is solid. The right side is worse than I thought.
See Video:
https://youtu.be/_vTm7Bqe2Jo
Pretty disgusted. Don't really want to hear any more opinions at the moment, but I am sharing this before going back to work the problem.
:mad:

Did you run a tap into the hole for a turn or so to dress the threads? Which sealant did you use?
 
This BETTER have fixed it!

After retreating to my home to compose the video and lick my wounds, I returned to the hangar with a vengeance. With the system already drained I detached the tubing from the upper and lower fittings and removed the offending right side elbow fitting. Evidence showed about four full threads of engagement after my last attempt.
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The gear leg fluid line was cleared with compressed air. The threaded hole was retapped about 2 more turns; the tap removed and the hole thoroughly cleaned numerous times with alcohol and compressed air, clearing it from the bottom up so any chaff would blow out the freshly rethreaded end. This process was repeated until I was satisfied that the threads were clean, healthy and deep; verified with inspection.
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The elbow fitting was thoroughly cleaned and recoated with Loctite 567 thread sealant, making absolutely sure that the sealant coated the threads completely. The elbow was carefully reinserted into the threads and tightened... and I mean TIGHTENED. I was just barely able to clock it to the correct position. The area was cleaned and the tube nut reattached. The engagement is significantly improved - from four threads to eight threads.
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The bottom flared fitting was reattached and both flared fittings were torqued and sealed. I will allow the assembly to cure for at least 24 hours; probably about 36 hours. Only then will another test be performed and captured with video. Based on the amount of care (and force) applied to this last repair, I anticipate success. Let me rephrase that: if the right fitting still leaks after this reassembly, I will lose all hope for this gear leg in its current state and it will have to come off. Please hope along with me that I won't have to face that. I've had enough setbacks on this project, thank you.
 
Hey Martin---this WAS a true AN822-4D correct----and not (what I call ) an imposter fitting? Even though NPT threads are supposed to be standardized all over the world, we have seen minor variances in non-AN versions.
Just asking.

Tom
 
Tom just beat me to it...
What if the fitting is defective???

I doubt that's the issue. I used two new (matching) fittings on the second try and they're the right spec. They're used in multiple locations and the upper gear leg fittings are the only locations that have had a problem. Tom, I'm hoping that minor variations are not the issue based on the purchase source. In every way I'm able to determine they are the correct and identical fittings.
 
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Couple of questions:

Goatflieg, what was the outcome? Success?

And would Loc-tite 243 be satisfactory as a sealant?

Or Permatex 57535?

I am about to seal the fittings for the sky designs version of the gear legs.
 
Once my A&P recommended or approved thread tape on brake lines. I objected but he said there is no fluid movement in our brake systems so is ok. He was very experienced and right - at least as far as I can judge.
 
Success at last?

My new gallon of Aeroshell Fluid 31 arrived today; drained old/flushed fluid into storage and refilled pressure pot with new fluid. Refilled and bled brake system; no spills, no leaks. I let it sit for awhile and for a moment I actually didn't want to test it because another leak would have really hurt... but I got back on the horse and checked both pedals: seems ok. Checked underneath: still no leaks; fittings and legs dry. Checked cockpit lines: tiny bubbles in each line. Bled both sides again and checked: solid pedals; no leaks; no bubbles, no fresh drips on the ground anywhere. I dare not convince myself that it's fixed until I check again tomorrow, but for now it's looking pretty good.
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Couple of questions:

Goatflieg, what was the outcome? Success?

And would Loc-tite 243 be satisfactory as a sealant?

Or Permatex 57535?

I am about to seal the fittings for the sky designs version of the gear legs.

I may have success; we'll see tomorrow. (see earlier post)
As near as I can figure (and I'm NOT a chemist), according to the Loctite 243 TDS, it is a dimethacrylate ester primarily designed as a threadlocker. Although the TDS does mention applying it as a sealer, it provides no specifications for pressure retention. If a dimethyacrylate is the the same as a methacrylate, then according to the Aeroshell chart it will withstand exposure to mineral oil-based and synthetic hydrocarbon-based hydraulic fluids. If they are not the same, well... I've no idea. Haven't checked on the Permatex.
 
Looks like I can report success too. Yesterday I removed the gear legs from the fuselage, removed the fittings and ran a tap down the holes cutting another couple of threads deeper. I replaced the fittings using Loctite 567 and had about two threads showing above the hole.

I reinstalled the legs and let the sealant cure for 24 hours. Today I refilled the fluid and tested the brakes. The pedals are firm and so far, no leaks.

I'm so glad I installed the bolt clips on the outboard bolts when I originally installed the landing gear. They make removing the legs an easy one person job. I had them off and back on in a few hours.
 

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