Leaking Brake cylinders

I'm having an issue with leaking 90 degree fittings going into the pressure side of three of four cylinders on my RV-9A rudder pedals. I've removed them once, checked the pipe threads, cleaned them, applied Permatex No. 2 to each, replaced them in their respective locations, tightened as tight as I felt was safe and they still weep when brake pressure is applied. The fourth fitting does not leak and all other fittings in the brake system are okay. The leaks are only at the male pipe threads of the 1/4" 90 deg fittings going into the pressure side of the cylinders. Any ideas as to a solution would be greatly appreciated. Thanks in advance.
Frank Bush

I used Leak Lock by Highside Chemicals with good results.

You could use the corresponding size steel fittings instead of aluminum (as was supplied by Vans). The steel doesn't leak - I never bothered to figure out why.

Dan

wish I could help, but ...

... the #2 Permatex and plenty of torque cured my brake leaks.

inserts installed?

The fittings will leak if you haven't installed the inserts in the tubing- have you checked this? Of course I'm speaking from experience. I had a pesky leak I couldn't stop until I noticed the inserts were not in the tubing where it goes into the fitting. The leak was so small that it would almost last until the annual inspection before the reservoir was empty. The ferrule will not properly seal without them. Same for your static and pitot tubing. When you purchase the fittings, the ferrules come with them but not the inserts. I've found several did the same thing and were not aware of it since the inserts were not included.

So...what leaks more often?

I get the impression from the many posts about brake leaks that the problem typically occurs as weeping NPT threads. I infer from this that the (properly installed) compression fittings are pretty much leak free. Yes?

gossend said:

I get the impression from the many posts about brake leaks that the problem typically occurs as weeping NPT threads. I infer from this that the (properly installed) compression fittings are pretty much leak free. Yes?

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Dick,

You are correct. I have one of the aluminum fittings that depending on OAT will seep at the NPT end.

I had one master brake cylinder that I could not get to seal no matter what (Matco). Thought it was from the NPT fittings but it was not. I finally figured it had a leak at the rod end. Removed the cylinder and found on close inspection that the rod was deeply scratched and it was not from me. I took the cylinder apart and in addition to the scratch's in the rod, found a chunk of aluminum shaving form the machining in one of the piston grooves. I polished out the scratches with the de-burring wheel, cleaned out the cylinders and reassembled with new O rings. No more leaks. My Matco split parking brake also leaked from new. What junk. The piston rod was dinged and did not look like it was machined at all, instead just formed hot then treated. That also needed polishing up and new O rings before it would seat up.

WOW! Matco junk??

Statistically, what you just reported would disqualify Matco as a supplier to any serious company I know of. I know my company (electronics) was allowed less than 10 defects per million parts shipped, or we got thrown out! Did you report this to Matco? What was their response.
Anybody else out there seen this sort of thing? its not too late to switch to Cleveland on my project. Id rather pay more than deal with hydraulic leaks...which always occur after you install the interior!

gossend said:

Statistically, what you just reported would disqualify Matco as a supplier to any serious company I know of. I know my company (electronics) was allowed less than 10 defects per million parts shipped, or we got thrown out! Did you report this to Matco? What was their response.
Anybody else out there seen this sort of thing? its not too late to switch to Cleveland on my project. Id rather pay more than deal with hydraulic leaks...which always occur after you install the interior!

Click to expand...

No I did not report it. Probably should have but then I am sure they would place blame on me somehow. Never had any problems with the Matco's on the Cozy MKIV and I attribute the leaks in the parking brake shaft to be both caused by pore manufacturing process of the shaft and the fact that it is a split design. If you over tighten the mounting bolts on the rubber washers, the two rotating valve body's have enough play in them to skew the two valve bodies and cause a leak. The valve body I put in the Cozy was the old one piece design (which the still carry) and machined from a solid piece of aluminum. It made for a more difficult install as one fitting had to be extended out so I thought I would try the two piece design. Finding a chunk of lathe turning in the master cylinder confirmed my thoughts that quality control was not in play the day my parts were manufactured. Perhaps "junk" is not a good term but I am (still) really tee'd off that I had to spend so much time tracking down leaks, draining, filling, bleeding brake lines multiple times, then repairing brand new parts in order to seal up the leaks. I never had a leak at any of my fittings. Sorry for my rant.

Threads on NPT are not always made with single point threading tools. Often they are made a tool that cuts all the threads at once. Since the feed rate can be high, when it stops rotating, it can leave what looks like a parting line along the length of the threads. I always inspect NPT threads for this defect. I found it on an air system installation. I began checking about 10 joints in and they all leaked. I ended up chasing internal and external threads on about 140 joints, but none leaked, and still don't 23 years later.

I have not found parts for my 7 like that yet, but still check.

Good luck.

We see this A LOT. Our first step is to try tightening and applying a generous amount of Teflon thread sealer ( the liquid stuff, not the tape) and get a good strong torque on it. If it still leaks, try new fittings. They are ever so slightly different and it is often necessary to swap fittings to get them torqued down and get the proper orientation. We haven't tried steel recently.

I too had leaking pipe connections on the cylinders. My mechanic told me to use teflon tape which I did and that helped. He said there is no fluid movement so tape is acceptable here. Now I also use Loctite 567 with success.

What about brass compression fittings?

So, i take it the main problem is the npt threads, not the compression fittings. Can the compression fittings be removed and then re-tightened like flare fittings can, or do they have to be cut off and replaced?