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Gun drilled gear - leaking brake fitting

fr0gpil0t

Well Known Member
The new gun drilled gear are great but I'm really struggling to get the one AN fitting to seal. A right angle elbow AN fitting screws into the base of the gear leg. It turns about 4 and a bit turns before bottoming out. I have to back the "bit of a turn" off so it is clocked correctly.

I've tried Permatex thread sealant, Permatex #2 and Loctite 567 and a new fitting but it always leaks ;-( No problems on the other leg.

I'm using a std 6in wrench to tighten the AN fitting - I could use something with more leverage but I really don't want to shear the AN fitting off.

I understand the principal of an NPT thread but wondering how I solve this issue. Tap out the thread a little so I can get the AN fitting to go in further ? Use a steel AN fitting - as the gear leg is steel.

Help please

Robert
 

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Earll’s plumbing

Check out Earl’s plumbing part number 923104erl or 923016erl. They are expensive but have a swivel on the pipe thread. Might work.
 
I would consider Teflon tape on stubborn leaky fittings. If you can, perhaps run a pipe tap deeper so you don’t have to back off the fitting to clock it.
 
Fitting

One possible cause of the problem is that once there has been hydraulic fluid on the fitting it is difficult to get a good seal without a through cleaning. Drain all the fluid and clean the gear. Aluminum fittings are generally not recommended on aluminum gear. A steel fitting would be better.
My standard sealant is titeseal. If you store titeseal in high temperatures it must be stirred to remix the components. A thin bladed screwdriver works well for this.
I see nothing wrong with four turns of engagement on the fitting. You may need to try several different fittings to find one that will "clock" properly while avoiding under or over torqueing.
 
I had troublesome leaks on my master cylinders that needed clocked, after some research on sealants: I cleaned the fittings/threads with acetone, sprayed the fitting threads with loctite primer N-7649 primer, then used loctite 567. I let the sealant dry for 24 hours then replaced the brake fluid. The waiting period was really what I changed from my previous efforts. Seemed to work for me. I did learn in the process that there are other loctite primers (e.g.7471) for colder temperatures.
 
Also, when you tighten the sealant progressively migrates in the threads. When you back off a bit then it isn't sealed.
Any of the approved sealants are fine, but getting it very clean first is smart advice. As is the advice to let it sit a day or so before pressurizing.
You say it bottoms out... how tight is it when you get to the correct clocked position without going past that?
 
Also, when you tighten the sealant progressively migrates in the threads. When you back off a bit then it isn't sealed.
Any of the approved sealants are fine, but getting it very clean first is smart advice. As is the advice to let it sit a day or so before pressurizing.
You say it bottoms out... how tight is it when you get to the correct clocked position without going past that?

Thanks this is good advice. It goes in about 3 and 1/3 turns using a std wrench for the last turn. Then I back it out about 1/3 of a turn which as you say will create a problem with the sealant.

I understand NPT fitting are tapered and by design get tighter. I think my concern is if I use something with more leverage it could go one of two ways. I could get that extra 2/3 turns to clock it correctly or the fitting could shear off ;-(. Is there a torque setting for these fittings I couldn't find anything.

Yes I cleaned this really carefully to remove all traces of the old sealant and left it 5 days before adding the brake fluid.

Robert
 
Someone may correct me but it is to hand tight plus 1.5-2 turns. All of mine are pretty tight with short wrenches.
 
For those that might be thinking of use a live swivel like the Earls 922104ERL,
understand that the ONLY sealing between the stem of the 90* body and the swivel NPT is an O'Ring. The NPT section is secured by a lock wire, so it will rotate. Great for orienting to a desired clocking. BUT, as the body moves, and it will with pressure cycles, and hose movement, the o'ring will eventually wear, and and the sealing capability will be reduced. Fluid compatibility is also to be considered.
This type of fitting is widely used in industrial applications, because its easy to use, but they eventually start to leak under no, or low pressures, They will seal under higher pressures because of the movement of the fitting. Not a good thing especially in brakes where everytime the pressure is decreased, you allow some amount of air to enter the system. Get enough and you have a spongy pedal, or worse.

PERSONALLY, I do NOT recommend use a NPT Swivel on any experimental aviation application. My 2 cents worth.

Tom
 
Thanks Tom I appreciate your understanding and perspective on this swivel fitting. I had not heard of such a fitting and was interested until more information was received.
 
I wanted to follow up and thank you everyone for their help - so far I think I have been successful.

Cleaned the fitting and gear leg careful, applied loctite 567 and put the fitting in hand tight. Then using a crowsfoot wrench and a medium length handle, tuned it smoothly just under 1.5 turns to the exact position, careful not to back off the fitting. Left the fitting 48 hours+ before adding brake fluid.

I think the difference between previous attempts was going a little tighter and not backing off the fitting to clock it. No leaks so far.

Robert
 
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