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Second Brake Line Failure

Skytrash

Active Member
My right brake line failed again right where it comes out of the AN fitting attached to the caliper. It has only been a hundred hours or so since the last failure which occurred at around 700 hours.

I think the second failure was caused by the caliper vibration due to chattering brakes. I replaced the brake pads after the first failure but not the disc. I think the brake fluid (Mil Spec 83282) was absorbed into the disc and is causing the chattering.

I am installing a new disc and installing flexible lines next week during annual.

Has anyone had problems with discs absorbing fluid and chattering?
 
First, I'll say I really haven't tried this on RV brakes, but it does work on automotive disks. I always bevel the leading edges of my brake pads with a file or grinder to about a 45 degree angle. It removes very little "life" from them and it really helps. I am getting ready to put on new brake pads on my 9A and will be doing it to them. I have noticed some chatter, especially when they are cold. They seem to smooth out after a few turns on the ground.

Bob Kelly
 
I think the brake fluid (Mil Spec 83282) was absorbed into the disc and is causing the chattering.

I am installing a new disc and installing flexible lines next week during annual.

Has anyone had problems with discs absorbing fluid and chattering?

Unless the disc is warped you're wasting you $, steel won't absorb brake fluids, just clean it with some acetone or MEK.

Nothing wrong with installing flex lines but if you make good flares and have a nice "loop" in the line per the drawing you should not be having any problems. I did upgrade this line to a 5052 at around 500 hours but it was just precautionary. Many many RV's have run for hundreds and even thousands of hours without problems so I think its safe to say there is nothing inherently wrong with the design.
 
Gary Bricker

I am a mfg rep for a major automotive brake co. The chamfer of pads is a major improvement to all brake pads. This has been found to cut down on chatter or noise in general. The piston contacts the pad and makes firm pad to rotor contact. Where the piston doesn't contact the pad vibration sets up. If the rotor is not smooth it multiplys the vibration. If it is warped then the pedal pulse is noted. When the pad is chamfered the contact surface of the pad is reduced and less chatter or noise is noticed. If you have fluid on the pad, install new ones. You cannot wash it out of the pad. If it is only on the surface sometimes you can sand the pad to wear it away. Pads are cheap. Replace them.
 
Thanks for the tip on chamfer of the pads. I will replace the fluid soaked ones with new chamfered pads.

After two failures I am going to replace the hard lines with flex lines. I do have a generous service loop on the lines and the flares do not leak but for whatever reason the line is failing.

I will eventually need to replace the disc anyway so I will be replacing the disc and I will clean up the existing disc for use when the other wears out.

Thanks again for the tip.
 
right brake chatter only

I have been reading the threads and this is my problem. I put new brake pads on both sides, installed new braided Teflon lines on both sides. Stainless rotors both sides. Bleed both sides with mil spec flood. The left side is Quit as a mouse, the right side chatters as soon as you touch the peddle and quits when you let off. I have chambered the pads and still have the noise. Any information will greatly appreciated.

Thanks Dennis
Rv6a
 
Stainless rotors both sides.
I've never heard of that. All I know is that stainless steel has 1/10th the thermal conductivity of carbon steel. To me it seems like a bad idea if you're wanting to dissipate heat.
 
brake

I had the main wheel sent to anti splat for the bearing upgrades. I will check to see if the bearing spacing is correct.

The left side had had a lot of cheese for the mouse.lol
 
Nothing wrong with using aluminum tubing for the brake line to the caliper. Thousands of RV's and others do it, and generally without any problems. Like Walt said, a nice loop, and make sure the line has some straight length before connecting to the caliper. That way the coiled part of the tube will act as a spring to absorb the vibrations. Really good flares are important. Make sure if using .035 wall that you dont over flare and thin the wall. We've seen most of the failures by breaking the flares at the base inside the sleeve. The nut pulls everything up tight, but the tube flexes, and cracks develop.

Yeah we make teflon hoses to replace them, BUT we know there are alot of planes the successfully use aluminum tubing in that area.

Tom
 
Chatter is from the metal brake lines

The metal brake line is causing the chatter.

Many certified aircraft have metal lines to a bracket close to the brake and then a short flex line to the brake.

Thats how my RV4 is,set up when I dumped the plastic lines supplied by Vans and installed Aluminum lines to the brakes no matter how I configured the loop in the lines I couldnt stop the chatter..until I added the short brake hose..and stainless disks are,a,waist of money..im my opinion.

Cm
 
Hope this isn't a thread hijack, but how do you make the transition from a compression fitting (as used for Nylo-Seal lines) to a AN flared aluminum line? Is there a fitting that is AN on one end and compression style on the other?

Is there another way to transition from nylon to aluminum brake lines without totally replacing the nylon with aluminum?

George
 
Worked for me

I found a weather head fitting that was sleeve compression on 1 end and 1/8 pipe thread on other then added a AN pipe to flare...been working great for 15 years and 800 hours

Cm
 
I really recommend using a aluminum tube down the gear leg, to an angle bracket riveted to the wheel fairing mount plate, with an AN bulkhead elbow fitting to a flex line with a loop to the caliper.

Some of the chatter is caused by the aluminum tube brake line itself, which acts like a spring. And of course, when it chatters, it is fatiguing the brake line.

With a tailwheel airplane, you are just asking for trouble if you don't provide enough compliance in the brake line. Losing a brake on landing is "interesting".
 
FWIT I installed 1/4" aluminum brake lines to caliper on RV-12 this morning and noticed after flaring the end of tube, the flaring device left a neat cut mark around the tube about 1/2" from flare. It looked like a point of failure so redid the flare...what caused it was flaring tool not screwed tight enough to prevent tube from turning when flare was done at end of tube.

The little cut mark is easy to overlook, it could be failure down the road.
 
how do you make the transition from a compression fitting (as used for Nylo-Seal lines) to a AN flared aluminum line?

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