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brake fluid leak and loose assembly

dbaflyer

Well Known Member
Went out to fly tonight and a few drops of brake fluid were sitting underneath my right wheel pant. Removed wheel pant and could not see any leaks in the fittings. The brake pads have plenty of ware left, but the forward portion of the brake assembly is loose, especially at the bottom. I am attaching a link to a video, hope it's accessible.

Still puzzled as to where the brake fluid is coming from.

Loose right brake assembly
 
My suspicion is that the leak may be from an oring that may be about ready to fail. I suspect that when you applied brakes after landing, the position extended. This may have been when the fluid leaked. When you released the brakes, the piston retracted and the oring stopped leaking. With a small amount of fluid, it may have taken some time to make its way to the ground.

You may want to take a closer look to see if there any evidence of fluid on the back of the plate the brake pad is mounted or on the housing underneath the pistons.
 
Since you are not versed on the mechanics of your brakes perhaps you should seek help in determining where your brake is leaking. No brakes at the wrong time would not be good.
 
Leaking brakes

A brake failure on a steer-by-brake plane can range from a problem to a catastrophe depending on when/where it happens. A number of planes have taxied into others or went off somewhere unintended and gotten damaged. A lot of people don’t seem to give this possibility much thought. Can’t say where your leak is coming from. Suggest you get access, clean up the area and apply some brake pressure to look for leaks. To dig deeper get the brake pads off the caliper and apply brake pressure while using a large C clamp to keep the piston from over-extending. If it is a piston O ring consider changing out the other side as well. They see some heat and don’t live as long. 5 years is a good life limit for these caliper O rings.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
It's either the piston O-Ring (most likely) or the brake line flare at the fitting has failed. There are no other places it could leak from. Check both since you'll need to open up the system to fix either.
 
thanks to all who provided good tips on what to check. This is solved. I had a helper watch down below while pressure was applied and the leak turned out to be a loose AN fitting into the caliper where the line attaches.
 
leaking master cylinder

During preflight, I noted the brake pedals were low on my 9A. Checked the master and it was empty. Removed the calipers and inspected the pads for wear and fluid. Wear was within tolerance but no fluid found. Climbing under the instrument panel I found the master cylinder was wet where it attached to the AN fitting that supplies fluid to left and right brake.

4G6Fho1r_t.png


I was able to tighten the AN fitting about 15 degrees and will keep an eye on it. I cleaned the old fluid off the firewall and use torque seal to make any subsequent movement obvious. Any other ideas and suggestions are welcome.

Thanks for this great thread.
 
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Another trick to find slow or intermittent leaks is to dust the suspected area with talc [baby powder]. Even a small leak will show up easily. Obviously, the talc will only stay in place on the wheel area during taxi with wheel pants on to block the wind. Works great for finding under cowl fuel leaks too.
 
I had a leak on one of my masters on my RV-10. I was sure it was from the AN fitting but no matter what I did to that fitting, I was always finding brake fluid there. I finally got fed up and remover the offending cylinder and upon disassembly found a good size piece of an aluminum machining chip inside which I believe may have put a small cut in the O-Ring. I cleaned the assembly and put in a new O-Ring,,,,,problem solved. At the time I was 100% positive the leak was from a bad AN NPT thread seal, as that is where the fluid collected and dripped from.
 
Last week I replaced the o-ring in the right brake assembly after it leaked. I replaced it previously in 2008. Yesterday I flew and there is still some brake fluid dripping. The OAT was 14F. Would temperature affect the o-ring sealing ability?

I am wondering if either the puck or the brake assembly is defective. The assembly is 25+ years old. Before spending the $ I would like to know exactly what is wrong. I can replace the o-ring again. Can a visual inspection identify a defect in the puck or assembly?
 
BRAKE LEAK

Replace the O-ring, inspect the cylinder bore for defects, rust, pitting, replace as required. Some people use crocus cloth to clean the inside surface and then wash it out with fresh fluid. Make sure the puck is properly positioned, the correct direction. Place some brake fluid on the O-ring as you push it in.

Also, practice NO BRAKE landings before needed. Plan everything you will do to bring the plane to a stop simulating a brake failure on one or both sides. The worst thing I can think of is to break a perfectly good RV because of a brake issue.
 
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