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Pipe Thread Sealant

n74846

Well Known Member
I have a couple of weeping brake fluid points on my master brake cylinders mounted on the pedals. Before I start the project I want to confirm that Teflon tape is the acceptable thread sealant to use with brake fluid. (I have already tried tightening the fittings with little improvement.)

Thanks for your input!
 
Teflon tape is not recommended. A paste type sealant is what you want. Now to start a 'primer war', I'd suggest either Loctite 567 pipe sealant, or Permatex #2.
I assume the leaks are from the NPT threads in the actual master cylinder. The line fittings, if correctly assembled, should not require sealant, and should not leak.
Cheers
DaveH
120485
 
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Technically, Teflon tape is considered a thread lubricant which allows the threads to be tightened further than without. It is not a sealant.
 
+1 for using Loctite 567. I had a leak in the same place and 567 fixed it nicely. Since I needed to drain all the brake fluid from my system to reseal the NPT fittings at the master cylinders, I also resealed the fittings at the calipers since they were also slightly leaking.
 
Before I start the project I want to confirm that Teflon tape is the acceptable thread sealant to use with brake fluid.
Thanks for your input!
Teflon tape is generally regarded to be off limits on aircraft, though I'm sure many get away with using it. And, in fact, my pitot line fittings came with some on the threads. Still, there's always a chance a bit of tape can get in the system and there are other alternatives that don't have the same downside. As others mentioned Loctite 567 or the Permatex equivalent, is a good choice, as is TiteSeal. I initially used fuel lube (EZ Turn) per Van's plans with good results, but others have had problems with that leaking. Now I just use the Permatex equivalent of 567.
 
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Thanks to all for the input. I will stay away from the Teflon and stick with one of the recommendations.
 
I used the Permatex #2 when assembling the brakes a couple of years ago. Last week at inspection the DAR noticed that every one of the Master Cylinder NPT fittings was leaking. Note that the brakes have had virtually no use since assembly. I'm in the process of disassembly, cleaning, and reassembly with Loctite 567 this time.
 
I use 567 on everything and have been happy with it. That said, I had several leaks in my brake lines as well. Even though carefully tightened with my expertly calibrated right arm, they leaked - even without actual pressurized use!. I took them all loose and did it over with more tightening force (and more 567) and now they are not leaking. There seems to be some slight mismatch on the threads of the fittings or the master cylinders, as well as some other places in the brake lines, and what I would call "over tightening" seems to solve the problem.
 
Post relevant to all RV's

I often see posts about people having leaks and changing to such and such sealant and thinking it fixed their leak problem.

It is very likely that a lot of the leaks on pipe thread fittings are caused by installation error rather than the choice of sealant that was used.

NPT threads on fittings are designed for a nearly net fit once properly tightened.
The thread sealant will take care of the last little bit of gap that exists at the bottom of each thread valley, but it does a poor job of sealing the rest of the thread area in instances where the fitting wasn't tightened fully. Particularly on high pressure hyd. systems such as the brakes.

This is not all that surprising since new builders that are "learning" have no way to know how tight is tight enough or too tight. It is also something hard to describe with verbal instruction. It needs to be good and tight, but not so tight it damages the threads. This is further complicated with a 45 or 90 deg fitting that has to be positioned at a specific clocking angle. It can be difficult to know when to stop or when to try for one more turn. Stopping one turn short of where you should can be a prime candidate for a leaking fitting in a high pressure system (brakes). In lower pressure systems (fuel) the sealant will do a better job of compensating for the fitting not being tightened as much as it should have been.

I believe a lot of the leaks get fixed by using a different sealant, because during re-installation they are tightened further than the first time, to help assure it doesn't leak again.

Loctite 567 is a great sealant and we use it for some applications in our shop, and it may help newbee builders because its lubrication properties may help them turn tighter than their limited experience makes them willing too, but many sealants will perform just as well, as long as proper installation technique is used.

BTW, a lot of the hate for the plastic lines and compression fittings is caused by people tending to under torque these also. The torquing process is deforming the internal compression barrel so that it seals around the line. They are not fully tightened until there is a significant increase in turning torque on the nut which indicates that the barrel has fully compressed.
 
Scott in your opinion are plastic brake lines acceptably robust and leak free? A lot of builders go with steel braided lines because it seems like it would be better. I know there are a million opinions but what is yours?
 
Scott in your opinion are plastic brake lines acceptably robust and leak free? A lot of builders go with steel braided lines because it seems like it would be better. I know there are a million opinions but what is yours?

I finished my RV-6 in the Spring of 1993. Plastic lines still leak free today.

Just one example.
 
Scott in your opinion are plastic brake lines acceptably robust and leak free? A lot of builders go with steel braided lines because it seems like it would be better. I know there are a million opinions but what is yours?

Every one of the company prototypes and demonstrators are built with the exact same parts shown in the plans and supplied in the kits.
Many of these have multiple thousands of hours (The original RV-6A has over 5000 Hrs) on them with no problems.

My personal RV-6A has the plastic lines.

So my opinion is that I think the plastic lines give excellent service if they are installed properly.

I hope that adequately answers your question.
 
This is not all that surprising since new builders that are "learning" have no way to know how tight is tight enough or too tight. It is also something hard to describe with verbal instruction. It needs to be good and tight, but not so tight it damages the threads. This is further complicated with a 45 or 90 deg fitting that has to be positioned at a specific clocking angle. It can be difficult to know when to stop or when to try for one more turn. Stopping one turn short of where you should can be a prime candidate for a leaking fitting in a high pressure system (brakes). In lower pressure systems (fuel) the sealant will do a better job of compensating for the fitting not being tightened as much as it should have been.


This was my issue on one of my eight fittings. I must have removed, cleaned and reapplied torque seal 7-8 times as well as trying 4 other fittings. All with no luck, then I finally said I will go one more revolution and get a good seal or crack the master cylinder. Lucy for me the extra revolution worked great an no leak.
 
This is a good thread re plastic brake lines, I'v got a very minor leak that probably just needs a bit more torque.

FWiW Loctite 567 is also good in the engine compartment for fuel fittings if needed, it has quite a high temp rating.
 
Every one of the company prototypes and demonstrators are built with the exact same parts shown in the plans and supplied in the kits.
Many of these have multiple thousands of hours (The original RV-6A has over 5000 Hrs) on them with no problems.

My personal RV-6A has the plastic lines.

So my opinion is that I think the plastic lines give excellent service if they are installed properly.

I hope that adequately answers your question.

Sure does. Thank you.
 
As Scott has mentioned, Pipe Fittings are an interference fit. Some of the parent material in the threads will slightly migrate to make a mechanical connection between the threads in the fitting and body.
If you have a fitting that you just can not get clocked properly, there are a few things you can do. First, work the fitting like you would a tap - turn back 1/4 turn, then forward, back then forward, until it is in the correct position. However, the final turn needs to be forward only. They slightest backward turn will break the mechanical seal.
I have found that not all fittings are manufactured identically. If you have one that is just not working out, try a different fitting. It might fit better.

As a last resort, you can clean up the threads in the body of the brake cylinder with an appropriate tap. You must disassemble the master cylinder so any of the small chips can be cleaned completely. Again, this is a last resort and should not be necessary. I recently did this because my cylinders where already apart and I had a fitting that simply would not clock correctly. It was an easy fix but not something I would recommend unless you know what you are doing. It would be quite easy to ruin a perfectly good master cylinder.

PS - Factory Plastic lines, 9 years, 700 hours, no leaks, ever....
 
It is better to use a pipe die on the fitting rather a tap on the female thread for clocking. It doesn't take much, the anodizing is barely scratched off in a few spots. Way easier to wipe off the male thread than to have to disassemble the master cylinder for cleaning.

Stewart Willoughby,
6 FWF.
 
Another Loctite 567 advocate here. On the NPT fittings, I clocked them correctly until they were snug, then wrench-tightened them another entire turn, to the clocked position. As a previous poster said, it's a real "feel" thing...if you've got a trusted builder a couple hangars over, it might be good to have him/her check your work. Felt a little Medieval, but no leaks whatsoever. I used the plastic lines for feed, and stainless-sheathed numbers for the high pressure side.

It's worth repeating that a very small smear of sealant is needed, with none on the first couple of threads.
 
It is better to use a pipe die on the fitting rather a tap on the female thread for clocking. It doesn't take much, the anodizing is barely scratched off in a few spots. Way easier to wipe off the male thread than to have to disassemble the master cylinder for cleaning.

Stewart Willoughby,
6 FWF.

Well, that certainly sounds like a better approach ;)
Mine was already apart but..... read my tag line!
 
A friend of mine, who is an accomplish builder, and a professional in the HVAC world helped me understand some things about pipe threads.
He said the sealant is also a lubricate used to tighten down a fitting where the pipe thread is an interference fit. This allows the installer to tighten the fitting to the proper orientation and will likely feel like "this is too tight and I am going to strip the threads!" He said better to tighten than too loose as it will likely leak.
I also helped with some black pipe gas installation and this guy tried to educate me on these pipe threads. It was pretty much the same story. The pipe sealant was to lubricate the joint and seal, but allow the installer to tighten to where the fitting needed to be so it would line up correctly.

I had a fitting on the brake caliper I could get to seal so I tried a different fitting and tightened beyond my comfort level. Nothing cracked or stripped and no leaks. Use good sealant like Loctite and tighten it well. Consider a different fitting if it continues to leak. Just my experience...good luck!
 
Thank-you Scott. All of my leaks were on pipe thread connections that were not tightened enough. I had originally trusted/hoped that the sealant would prevent leaks in a fitting that I was afraid to tighten another full turn. Crank away! I liked the "Medieval" reference, Doug!
 
Looking back on tightening my brake fittings I question the torque I applied. I cranked down on them quite a bit which I wonder if it was prudent, but they don't leak!
 
Do the leaks occur only at the NPT fitting, or do they sometimes occur at the compression fitting? Approximately how many times can the compression fitting be removed before causing leaks? After reading this thread, I'm considering re-doing all the brake cylinder fittings with Loctite 567 and a bit more torque.

Jerre

I used a Permatex thread sealant with PTFE (Teflon) in it. The PTFE provided the lubrication needed to get one more full turn on the fittings into the brake cylinders.

https://www.zoro.com/permatex-threa...JxFipBCpnOhI1iIFgAlo4aAnaG8P8HAQ&gclsrc=aw.ds
 
Jerre -

I have had four leaks thus far .... three on the brake lines and one fuel.

All of them have been at the threaded NPT fittings.

Three of the leaks were where the fittings screw into the master cylinders for the brakes. I was able to fix two of them by clocking the fitting tighter then removing it and reapplying 567 thread sealant and tightening to the final position. However, one fitting still leaked so I replaced the fitting and used some medium bodied TiteSeal and the issue was resolved. I think the threads on that master cylinder were a little deeper than they should have been.

The other leak was a fuel related leak coming from the NPT threads on the CAV-110 fuel valve screwed into the bottom of the gascolator. This leak took a couple of months to develop. Tightening the valve would not solve the issue. So because it was brass/aluminum coming together, I feared making things any tighter (it was darn tight at this point), so I chose to just replace the CAV-110 valve and here again used TiteSeal. It has been a couple of months now and no leaks yet.

Happy Building,
 
So because it was brass/aluminum coming together, I feared making things any tighter (it was darn tight at this point)
Sounds like you successfully avoided repeating my long-ago (my RV-6 era) mistake of applying the JOMT methodology to gascolator work:

"I put the spark plugs back in this evening, and was going to call it a day when I decided to go ahead and put the gascolator back on. I'm been having a problem with the threaded knob that holds it in place being difficult to remove and replace, and today was no different. I got it as tight as I could, but when I turned on the fuel pump to leak test it, I found that it still leaked. This is when I decided to apply the JOMT (Just One More Turn) methodology, and as is usually the case, I went one turn too many. I broke the threaded knob thingy."
 
Installing my AN fittings now. People here are referring to Loctite 567 whereas Van's section 5 suggests Loctite 565. Which is correct? Both perhaps?
 
AN fittings should not use sealant of any type.On NPT fittings, like the ones in the brake cylinders, I would recommend either permatex#2, or loctite 567. Use sparingly on the tapered thread of the fitting.
Cheers,
DaveH
120485
 
MATCO recommends Loctite 567 for their brake fittings. I have had very good success with 567 on all of my RV-12's threaded (oil, gas, brake, etc.) NPT fittings. My local hydraulics supplier had it available in small tubes.
 
AN fittings should not use sealant of any type.On NPT fittings, like the ones in the brake cylinders, I would recommend either permatex#2, or loctite 567. Use sparingly on the tapered thread of the fitting.
Cheers,
DaveH
120485

I'm talking about the AN 822 4D fittings that screw into the master cylinders. I used Permatex #2 there. I'm confused by what you've written. In section 5 it states that all threaded fittings (including the AN fittings which have an obvious taper) used on an RV are NPT and thus require sealant.
 
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MATCO recommends Loctite 567 for their brake fittings. I have had very good success with 567 on all of my RV-12's threaded (oil, gas, brake, etc.) NPT fittings. My local hydraulics supplier had it available in small tubes.

Thanks Dave. I used Permatex #2 on the master cylinders (couldn't locally source the Loctite). The stuff is nasty like Proseal however. I ordered Loctite from Acklands Grainger and will use that from now on. I just wasn't sure which to get.
 
The tapered part of the thread, eg the part that threads into the master cylinder, requires sealant. The AN nut and flare connections such as you will find on the fuel lines will seal by their design. They should not have sealant on them.
That permatex can be a bit sticky. When I was mechanicing(?) we cleaned up with a little IPA. It's still a good sealant and will certainly do the job.
Hope this helps
Cheers DaveH.:)
 
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The tapered part of the thread, eg the part that threads into the master cylinder, requires sealant. The AN nut and flare connections such as you will find on the fuel lines will seal by their design. They should not have sealant on them.
That permatex can be a bit sticky. When I was mechanicing(?) we cleaned up with a little IPA. It's still a good sealant and will certainly do the job.
Hope this helps
Cheers DaveH.:)

The other side of that fitting has even a more pronounced taper Dave. I'll have to do a bit more research to try and understand what you are saying because i thought that both sides needed sealant.

Who would have thought that Indian Pale Ale had so many good uses! ;)
 
:D I like your thinking on the IPA. Don't waste the good stuff on cleaning up. Save it for later.
What I'm getting at is that you have to seal the threads, such as where the fitting screws into the master cylinder. The 'bit with the nut' such as the brake tube end, is designed to seal mechanically. That little brass thingy that we Aussies call an olive, is trapped between 2 opposing tapers. The force of the nut pushing down on it makes it bite into the outside of the plastic line, producing the seal. Assembled correctly, no sealant should be needed.
Similarly the AN 37.5 degree fittings rely on a clean finished taper to make the seal mechanically. No sealant should be needed.
Clear as mud, eh?
Love your tail number, that's what my grandkids call me.
Let's go oilers
DaveH
 
Another thought: Be sure that whichever sealant you use for your fuel line fittings, that it is compatible with the ethanol in your fuel (if you use ethanol-poisoned auto gas). As I noted earlier, the Loctite 567 on my RV-12 is working very nicely to date.
 
Another thought: Be sure that whichever sealant you use for your fuel line fittings, that it is compatible with the ethanol in your fuel (if you use ethanol-poisoned auto gas). As I noted earlier, the Loctite 567 on my RV-12 is working very nicely to date.

Thanks Dave. No mogas for me. My engine is going to have 9:1 compression and the builder didn't recommend that it be used. I ordered both the 565 and 567 just to be sure that I had the correct stuff on hand.
 
:D I like your thinking on the IPA. Don't waste the good stuff on cleaning up. Save it for later.
What I'm getting at is that you have to seal the threads, such as where the fitting screws into the master cylinder. The 'bit with the nut' such as the brake tube end, is designed to seal mechanically. That little brass thingy that we Aussies call an olive, is trapped between 2 opposing tapers. The force of the nut pushing down on it makes it bite into the outside of the plastic line, producing the seal. Assembled correctly, no sealant should be needed.
Similarly the AN 37.5 degree fittings rely on a clean finished taper to make the seal mechanically. No sealant should be needed.
Clear as mud, eh?
Love your tail number, that's what my grandkids call me.
Let's go oilers
DaveH

Yes Dave. Tom at TS Flightlines confirmed what you said. Thanks for saving me from a mistake! :) I owe you an IPA or two! :D
 
MATCO recommends Loctite 567 for their brake fittings. I have had very good success with 567 on all of my RV-12's threaded (oil, gas, brake, etc.) NPT fittings. My local hydraulics supplier had it available in small tubes.

I've been trying to find the Loctite 567 with no joy. It's on the NAPA website but they (the company) are completely out.

-Marc
 
What am I missing?

I purchased Loctite 567 recently because it is so highly recommended here. However, I have used Locktite 515 for years on cars, antique airplanes and my first RV. I get the teflon lubrication. Both are anerobic cure. 515 is for thin gasketing. I clock the fitting as needed without excess torque and count on the 515 to seal any thread voids. No leaks, so educate me why 515 is not another good option.
 
I see the referenced product is shipped from China. Is that where all Loctite is produced, or is there a risk of a 'knockoff'?
 
No. A few posts back Jim posted an eBay link for the product at about $6.50. I suspect that answers the question to the affirmative.
 
I have used Tite-Seal in the past http://www.aircraftspruce.com/catalog/cspages/tite-seal-04-03925.php?clickkey=23262 but after reading through this thread I am now thinking I might want to switch to the Loctite 567. :confused:

For another data point ... I used Loctite 567 on the aluminum fittings that screw into the RV-12's brake master cylinders and had multiple leaks which after removing /cleaning/reapplication of the 567, still had the small seepage.

I decided to try Tite-Seal .... it solved the seepage issue. So a +1 for Tite-Seal from me.
 
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