Sealant For Fixing Brake Leak

[AMK53]

I have a brake fluid leak in the center of my tygon tubing that goes from the gear legs into the brakes. Unfortunately the tubing is under fabric already and I'd really rather not tear it apart to replace the tube. Is there some kind of sealant that I can use to patch up the hole without replacing or cutting the tube?

26651

[Dave S]

Hi Ali,

There are several things to think about here - above all a person wants brakes that won't fail.

First off - just to help you with the terminology, the tubing is not tygon, the correct name is Nylaflo. The stuff is made of nylon, hence the brand name. It should be 3/16" on the OD.

I have no idea how old the installation is or how much wear and tear has occurred over its service life, but there is a limit, which nobody seems to know for sure as to how long it would be safe.

As much as the option is not savory and involves additional work, I believe the best choice would to replace the tubing and the compression ring under the nut (the ring is not reusable).

Some of us have used braided aviation brake line with AN fittings on the calipers simply because this is an area on the plane subject to a lot of abuse due to what we drag our wheels through. This is quite expensive.

Best of luck

[AMK53]

Thanks, Dave. It’s not just about being more work. The original builder routed the tubing through the gear legs under the fabric continuously. I would have to tear up all the fabric just to replace that small 4” length. It seems to me there should be a reasonable in between. I wonder if I can cut back the tubing close to the yellow extrusion and then put a new compression fitting there that would go from compression to AN. Then I can do a metal braided hose from that down to the brakes. is the fitting on the brake caliper NPT to compression?

[3 tracks]

This is what I did. Remove line at brake caliper cut the fitting off. Where the line goes in the gear at the top cut it off. I used a piece of 9/32 cable, run through the line. Run new tubbing behind it at the top. With a helper, pull from the bottom and push from the top. Pull line and cable together, don't let it slip. Very easy to do, I replaced mine with braided line.

[Dave S]

Ali,

I think 3 tracks has a great idea for this predicament.

[Maverick]

During the last month of the build on my KF5 I was stepping around the left wheel. I brushed up against the Nylaflow tubing and the next thing I knew I had brake fluid running everywhere. The Nylaflow broke about four inches distal to the fitting and about two inches proximal to the slot in the back of the gear leg. The conditions of storage of this tubing are unknown except for the time that I owned it but, from what I've been able to find, Nylon brittleness is usually caused by cycles of water absorption and depletion. This was Nylaflow that came with the original kit from 1995 which has been in Phoenix all this time so the brittleness of it is no surprise. I replaced every inch of the Nylaflo with braided brake lines I bought at RamJet performance shop. The point is that if you have a leak due to a perforation in your tubing, you are likely going to be chasing others sooner than you really want to. Remember that those brake lines are moving around with rudder pedal movement.

IMHO, this is a disaster waiting to happen. In the absence of any manufacture's data to suggest a safe life expectancy of the tubing and under which conditions, you might want to bite the bullet and replace all the Nylaflow. A little fabric work can be fun and rewarding. Rebuilding a wing due to a ground loop, not so much. Or worse.
Fred

[Dave S]

Maverick,

Thanks for your update on the nylaflow product. I have also been bothered by the fact that there is no information on useful life of the the product.

I did take the time to drill down into the manufacturer's specs for the Nylaflow that came with our kit which is identified as 3/16" T type, thin wall tubing good for 1000 PSI burst pressure according to the Nylaflow specs. Interestingly enough, the heavy wall (H type) good for 2,500 psi cannot be used with the same tube nuts for some reason.

As far as environmental compatibility, there is some useful info but not a lot. The manufacture labels "excellent" resistance to the stuff that is in aviation brake fluid but not so much for auto brake fluid. The other issue on chemical resistance is that it has "poor" resistance to zinc chloride and "fair" resistance to light (without saying which wavelengths).

I wonder if the "fair" resistance to light may be one of the reasons that would set us up for a higher failure rate on nylaflow exposed on the outside of the aircraft like on the gear legs?

Oh yeah, and there is a lot of sunlight in Phoenix.

[Meyer]

Yes try to use the old tube as a snake for the new.

[AMK53]

Thanks for all the advice. I was originally under the impression that I had a very small pinhole puncture just due to me working around the airplane so much in the past 8 months. I started doing more thorough leak checking and it looks like all the leaks are actually occurring at the fittings. I tightened them down a bit more and it stopped the leakage. I'm not sure how they came loose in the first place as I haven't messed with them at all and it hasn't flown for almost 8 months.

I do want to replace the lines outside of the aircraft with metal flex lines at some point though. It seems like a bad idea to have nylon tubing sitting by the wheels.w

[AMK53]

Unfortunately it looks like I’m still leaking out of the compression fittings. Do nylaflow tubing need inserts to properly seal?

[jiott]

Yes they do.