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How tight for 90 degree brake cylinder elbows?

cnpeters

Well Known Member
For AN822-3D 90 degree alum. elbows that attach to my brake pedal cylinders (Bonaco brake lines attach on the nipple ends), how tight have folks tightened these as they rotate them in? Just put fuel lube/EZ turn and tighten 'til fairly tight, or do folks torque these?
Thanks
 
Run it in by hand, then on the next turn with a wrench, set it at the direction that you want. It is small........ use a small wrench.
 
I had a problem with both my lower left master cylinder fittings leaking. It seams that the tap used by Matco left some scoring across the threads. One of them I had to crank in pretty hard and used fuel lube. The other I gave up on and sent back and received a credit from Vans. Do a search there has been discussions here recently.
 
After getting a pipe thread hand tight, you will have at least one full turn available for "setting" the direction you want.
 
I'm not a pipe fitter but I have done extensive pipe design as well as being a mechanic for 25 years. From this I have had NO good experience with pipe threads. I can not remember an OEM application that used pipe threads on brake components, they leak! The auto manufacturers have been eliminating pipe threads from every component and replacing with gasketed or o-ringed seals. It surprised me that aircraft use pipe threads on brake components.

I have found that installing pipe thread elbows is a bad idea. It is best to install straight male connectors and put the elbow on the hose. If space does not allow than you will have to use the elbow. You will very likely find that where the elbow seals and where it needs to point are never the same. Do not back off a pipe thread fitting to position as it will leak. Over tightening can split the housing. Be very very careful using sealants with brake fittings for fluid compatibility, I would recommend dry fitting I would not recommend using Teflon tape on brake fittings as little pieces of tape can easily get into the system. I would look for components that do not use pipe threads especially on brakes. Pipe threads do not do well in vibrating conditions, they loosen and leak!

I have only found two types of pipe threads; Those that ARE leaking and those that are ABOUT to leak. If any of the components are stainless steel they will always leak.

Sorry for the rant but NPT threads are not suitable in my opinion for anything other than your water taps at home.

Bob Parry
 
Everyone's experiences are different, but I have been an auto mechanic for almost 50 years and an aircraft mechanic for 35 years and have never had a problem with pipe threads in any application. I do use a sealer, Permatex Form-A-Gasket.
 
Everyone's experiences are different, but I have been an auto mechanic for almost 50 years and an aircraft mechanic for 35 years and have never had a problem with pipe threads in any application. I do use a sealer, Permatex Form-A-Gasket.

I use HARVEY'S TFE PASTE with teflon. I think that it acts more like a lubricant for the threads so they will seat better.

Inspect the threads on both parts. If they are not GOOD, then it will leak no matter what you put on the threads.
 
What else have people had success with? My elbows are still leaking. I have them plenty tight and used fuel lube. On the plus side, I'm getting really good at bleeding brakes.

-Rob
 
Fuel Lube, and tighten them like tapping threads.

I use fuel lube and have no leaks. Unless they match up perfectly in orientation the first time you tighten them, which is rare, you will need to "work" them into position. This is done by backing them off a quarter turn, then tighten, then back off, then tighten, just like when using a tap for threading. You may need to remove them and clean the threads, then try again. Once you get it into position do not back it off or it may leak.

You may find a fitting that will not allow you to get it into position. Try another fitting. They are not all machined alike.
 
Thanks, Jon... what you described is exactly what I did. When I did it originally, one leaked, so I tightened it pressed on the pedals a bunch, with no problems. After I did the first engine start last weekend, though, I noticed a couple drops on the floor from both sides, so I was probably pushing harder.

I'll take them out and clean the threads, but will be looking to use something more "robust" on the threads this time.

-Rob
 
Make sure it is that side of the fitting...

Thanks, Jon... what you described is exactly what I did. When I did it originally, one leaked, so I tightened it pressed on the pedals a bunch, with no problems. After I did the first engine start last weekend, though, I noticed a couple drops on the floor from both sides, so I was probably pushing harder.

I'll take them out and clean the threads, but will be looking to use something more "robust" on the threads this time.

-Rob

I had the same thing and thought it was the pipe thread but it actually was the tubing/b-nut fitting. It is very hard to tell where the leak comes from as the fluid can run down and pool around the pipe thread making it look like it is the culprit.
Also, the master cylinders can leak a touch from the seal when you first start messing with them. I had a small leak on one cylinder but after a few pumps it cleared itself up.
 
In the same boat

Like the OP, I used EX-turn. The left master cylinder leaks at the fitting. I have not installed the forward baggage floor and have great access, and I can see the fluid coming out around the fitting, so I know this is where it is coming from. I drained the brakes and tried permatex with the same problem. After doing a few searches here, it seems Loctite 567 or Bakerseal are the preferred sealants, but it also seems that several folks have had success with EZ-Turn. I'm going to give it one more shot and it if it isn't working then, I'm going to swap the MC out and see if that does it.

By the way, I went ahead and swapped sealant on all NPT fitting on the MC. This is still the only one leaking.

Also like you, I have also gotten quite good at filling the brake lines.....
 
Teflon tape isnt a good choice, for all the above reasons. BUT, NPT sealer with teflon ( the paste) works well. When you are doing your mock up assembly, mark the cylinders where your AN822-4D's should point (sharpie). Seal the fitting, ans after hand snug, you should be able to get them to tighten up and index to the mark. Be careful on aluminum to aluminum, and really cranking on them---yep you CAN break a fitting, or strip the cylinder.

Ive been using this teflon paste for years in alot higher pressure applications than RV brake systems with no issues. Its all in the preparation.
Tom
 
pipe threads

This seems to be a never ending subject, I have been working around aircraft for 40 years and have always used fuel lube on pipe threads. This was from instruction by my first boss who was an experienced and military trained AME, A&P. I learned years ago that you do not put aluminum pipe fittings together dry unless you want to order new fittings. I feel that most times pipe fittings leak they are not installed tight/deep enough. I also think that pipe fittings seal because of their design, taper, and not because they have a compound of some sort applied. The reason for applying fuel lube, EZ seal or whatever you choose is to lubricate the thread and allow it to go together further and tighten/seal deeper into the taper.
 
Leak fixed

My hangar neighbor (Zenith builder - DAR inspection this week!) had some Bakerseal that he used on his plane. He got it from Aircraft Spruce and is enough to last several lifetimes. It looks very similar to the paste compound you can get in the plumbing section at any hardware store, but says specifically that it is made for use with hydraulic fluid (and many other things.)

I took the leaking fitting out and cleaned it very well with a brush and some solvent. I also cleaned the female thread in the same manner until they were shiny. I then applied a liberal amount of the paste to all but the first thread and installed it. Reconnected everything and filled it.....Voila! Leak free.

On to the next item on the list....
 
One leakes...

What a pain. The bottom fitting on one of my pedals leaks! I originally used Fuel lube. Then I tried permatex #2, but it still leaks. And I've not figured out how to efficiently put the brake fluid back in. Painful, painful!

I think I'll try Bakerseal. AircraftSpruce doesn't seem to carry it anymore. Where did you get it from?

Michael-

p.s. Just doing a little complaining.
 
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If your NPT thread is leaking, I believe it is 1/8" NPT pipe. A typical tap and die set has this tap in the set. Thread it in and turn maybe 1/8 turn and then see if it seals. EZ turn is a lubricant not a sealant, so go back to #2 permatex or #3 which ever you have on hand. Sometimes a rapid production threading for NPT leaves an axial ridge line where the tap stops and that is where the leak initiates. Especially if it is a single point threading tool. Just honking on it with lubricant might work but it also might break the housing. It IS tapered! So . . . not recommended.

Good luck
 
I hate fuel lube! I've had excellent results with both Tightseal and Bakerseal. Pipe thread fittings must be very tight, most folks tend to be scared to tighten them enough. Never use aluminum fittings in aluminum threads.
 
just saying

If you are planning on taking a 1/8 NPT tap and chasing the the treads, and making a 'better' solution, remember NPT is a tapered thread, so if you thread the tap deeper into the hole, the top will be slightly wider when finished, So you'll have to screw the adapter in further for the threads to interlock. Even with your favorite sealant, it may not solve the issue. Yep---I actually saw a really nice master cylinder with a broken thread section of an AN fitting in it due to the re-engineering of the cylinder. Be careful.
Tom
 
I used Loctite 567 on all of my pipe thread fittings and it has performed great. No leaks.
 
titeseal

I hate fuel lube! I've had excellent results with both Tightseal and Bakerseal. Pipe thread fittings must be very tight, most folks tend to be scared to tighten them enough. Never use aluminum fittings in aluminum threads.

plus one for titeseal. One of my early mentors convinced me of this many years ago. Never a problem with titeseal. If it is stored in an extremely hot environment you must stir it with a small screwdriver or something similar because it does separate in hot environment.
 
As crazy as it sounds, I once heard that steel (instead of aluminum) fittings would help prevent leaks. So, I put them in and, as an anecdotal sample of one, can report - no leaks.

I have seen the teflon tape used with some success (absolute heresy!) I'd be very careful to start it up several threads to prevent any debris from getting into the brake cylinder.

Dan
 
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