P

prkaye

Well Known Member
First, let me carefully don my flame-suit, in case this is the most ludicrous idea ever...
I, like many people, have had a persistent problem with weeping through the pipe-threads of the AN elbows in the brake master-cylinders. I used fuel lube on all of them, and really had to tighten up several after installation (the rule everybody quotes is hand tight plus up to one full turn... I've had to tighten them all more than this... approx two full turns after hand tight). Since then, all have been ok (no leaks), except for one (pilot's side brake, lower (high-pressure side) fitting). I recently replaced the master cylinder and fittings, and have tried TiteSeal, and most recently Permatex High Temp Thread Sealant (I know it doesn't need to withstand temps, but that's the product they had at the store). Once I get it hooked up again and give it a couple days I'll know if this worked.

So, here's the idea - if the leak on this fitting still persists, what about using a small torch and running a bead of plumbing solder around the joint? Presumably hardened solder would not be adversely affected by hydraulic fluid? Would the pressure of the brake fluid behind it pose a problem? Would the heat of the soldering torch melt or deform the aluminum fitting? Is there another reason why this is a stupid idea?
 
Last edited:
DO NOT SOLDER!

I've used Permatex #2 on pipe threads for over 40 years and virtually never experience leaks.
 
No flaming allowed toward you or the airplane :) Please do not try to solder the fittings! If the fittings leak they are not tight enough generally. Most seem to be afraid of over tightening the pipe fittings but if you have used THREAD SEALANT, (I perfer teflon based) to eliminate the chance of galling, and they still leak, they probably need one more scary turn. If necessary, turn the fitting back and fourth during the last turn. I've done many pipe fittings and still once and awhile have to go back and tighten one because of a slight leak.
FWIW- the cylinders do have internal O rings and I wouldn't advice using a touch or that kind of heat anywhere onyour RV.

Larry
 
Last edited:
Anyone reading this thread please repeat after me:

I will not use Fuel Lube to seal pipe threads.
I will not use Fuel Lube to seal pipe threads.

There, thats much better.

Fuel lube is a LUBE (duh) not a sealant. Otherwise it would be called Fuel Seal. :D

I swear by Titeseal, works great. As a SEALANT. Tite SEAL...get it?
 
Proseal

Proseal is another great alternative.
You can easily open them again if you have to.
While I observe proper torque values I think the values given for AN fittings
especially the pipe thread ones is way too loose.
However, an over torqued B nut is more likely to leak and fail than an under torqued one.
 
Soldering aluminum is difficult. I do it on aluminum condenser and evaporator coils occasionally. You have to have itvery clean, use the proper flux and solder. Like others said, don't try it on a plane.

I use leak lock by high side chemicals. Good for 400F and 10,000 PSI. Get it at your local hvac dealer or distributor in 1.3 oz tubes.
 
Heat!

prkaye said:
Ok, but why?
Click to expand...

Because in all likelihood, you will warp the bore of the master cylinder. You would in effect, simply trade one problem for another[even worse]. I like Permatex pipe dope with Teflon. Bob's favorite, TiteSeal, is another good one.

Charlie
 
No plumbing solder

Don't believe the typical tin-lead plumbing solder will bind to aluminum. There are welding materials for aluminum of course, but not all alloys can be welded, and you would probably have to remove any anodized finish. I would use Tite Seal
 
I have also heard of people chasing a leak at the master cylinder and eventually tracing the problem to the fitting bottoming out before it is completely sealing. They filed a bit off the end, carefully deburred and could then turn the fitting until the taper sealed in the hole.

YMMV and it could be bunk...:rolleyes:

Jeremy Constant
 
I have seen the caliper body cracked more than one time at the fitting from overtorquing the elbow,,,inspect the area around the threads for cracks,,,
 
Almost Fool Proof!

It may cost more to fix if you started with a 45 or 90 fitting at the caliper and it did not work.

The sure fix is to put in a straight nipple at the caliper, seal and tighten to acceptable low to medium of the specified tightness.

If you need an angle, put an angled fitting on the hose end.

If is still leaks at the caliper pipe thread, you can loosen the hose and turn the straight fitting a small or large amount to solve your issue.

The angled brake hose end that connects to the straight nipple will not be affected!
 
Cleanliness is next to..

From the good advice above,pick a sealant. In my opinion, your best bet will be removing the caliper from the aircraft, removing the fitting and cleaning everything with a good solvent. I personally like isopropyl alcohol, but I expect others will have their own favorites. In the old days we used nasty high VOC solvents that worked really well and destroyed our brains and other body parts. Perhaps you can tell from some of our (my) posts :)

LarryT
Larry Tompkins
RV-6A W544WB
W52 Battle Ground, WA
 
sealing pipe threads

People tend to think that because pipe threads are tapered, they will seal by reaching an interference fit when tightened. This is true on the flanks of the threads, but not at the apex of the threads where there is a small radius at the root of the female thread, and a slightly larger radius at the crest of the male threads.

The apex of the thread forms a helical (spiral) leak path no matter how tight you tighten the fitting. You MUST use a thread sealant. Period.

Sorry to beat a dead horse, but:
Good luck ever soldering to aluminum. With exactly the right braze alloy and flux and loads of practice, on exactly the right alloys, it "can" be done, but it is extremely difficult. And certainly not on a hydraulic cylinder.
 
Thanks for the info Steve! In my post above, I should have mentioned that sealant was used both before, when it still leaked, and after. I believe it was the white, teflon based pipe sealant. But you're right, I was under the impression that the pipe threads were supposed to seal without sealant. I just thought I was inferior because I never had any luck without using the PTFE (Teflon) thread paste so I just use it as a matter of course. Thanks for the education!

Also, it appears there's some confusion regarding which fitting was leaking. I think the original post is refering to the master cylinder, not the caliper...

Jeremy Constant
 
Cleanliness is next to ....

jjconstant said:
Thanks for the info Steve! In my post above, I should have mentioned that sealant was used both before, when it still leaked, and after. I believe it was the white, Teflon based pipe sealant. But you're right, I was under the impression that the pipe threads were supposed to seal without sealant. I just thought I was inferior because I never had any luck without using the PTFE (Teflon) thread paste so I just use it as a matter of course. Thanks for the education!

Also, it appears there's some confusion regarding which fitting was leaking. I think the original post is referring to the master cylinder, not the caliper...

Jeremy Constant
Click to expand...

Jeremy,
Another issue when using a sealant in a tough to seal situation, is to let the sealant cure in a clean [no fluid] environment for at least 8 hours. I'm a fan of the Permatex Pipe Sealant with Teflon you mentioned. I use it on lots of stuff, including sealing the fittings on my pneumatic tools. Due to the high pressure [135 psi] and thin fluid [air] I've found that if I don't let the sealant dry first, the results are not always the best.
Since the brake master cylinders can generate up to 800 psi, they fall into that "tough" category. Best to make sure that the master cylinder or caliper is dry before applying sealant and the fitting. Give the sealant 8 hours to dry prior to filling the system, for best results. I've also used SealTite, with excellent results.
Charlie
 
You must log in or register to reply here.