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Brake Question

bill.hutchison

Well Known Member
I have recently replaced pads and bled both brakes. Pedals are firm.

At my airport, I have to taxi from the hangar line to the taxiway down a short incline/hill - nothing TOO aggressive, but I do have to ride the brakes down it to keep from going too fast.

My right brake has been making a noise - not a squeal, but more like a deep....squeak. Think of a sound close to a French horn.

The brake pedal feel - as I said - feels the same in both pedals, but it feels like the caliper isn't grabbing as tightly and the brake doesn't have the same holding power. If I hold the pedals and do a run up to 2000RPM, I can feel the right trying to break loose and I have to press much harder to hold it.

Braking action on rollout has been fine up to this point, but I'm worried about it because it's not supposed to be this way and I don't know why.

I thought about re-bleeding it but if the pedal pressure is the same as the left, (which works fine) is that really the issue?

I'm going to inspect tomorrow but wondered if there was something specific I should be looking at?
 
Holding/not holding during runup is a traditional test of pads that have/have not been properly conditioned. Try one or two firm stops from a modest speed taxi (or whatever your pad manufacturer says), let cool, test again.
 
Brakes

Check the caliper pins to see if the pad is sticking in the pins.
May need a little lube on the pins.
 
Holding/not holding during runup is a traditional test of pads that have/have not been properly conditioned. Try one or two firm stops from a modest speed taxi (or whatever your pad manufacturer says), let cool, test again.

I'll do that. I've read that the Rapco brake liners need to be conditioned. I've also read that the SAME brake liners do NOT need this. <shrug>

Check the caliper pins to see if the pad is sticking in the pins.
May need a little lube on the pins.

Did some searching. Turns out I have some anti-seize in the shop so I'll use that.
 
I had exactly the same issue on new brakes but it didn't seem to affect brake effectiveness. It was a loud moaning kind of sound, I figured it was the pads dragging slightly.
I lubed the pins, adjusted the brake lines and even put on new disks to no avail.
I was going to put an .040 spacer between the caliper and brake housing, to create a little extra space between the pad and disk but first, I chamfered the edges of the brake pads with a file. Basically putting a small 45 on the edges. After a couple of flights the noise stopped completely.
Hope this helps.
 
I had exactly the same issue on new brakes but it didn't seem to affect brake effectiveness. It was a loud moaning kind of sound, I figured it was the pads dragging slightly.
I lubed the pins, adjusted the brake lines and even put on new disks to no avail.
I was going to put an .040 spacer between the caliper and brake housing, to create a little extra space between the pad and disk but first, I chamfered the edges of the brake pads with a file. Basically putting a small 45 on the edges. After a couple of flights the noise stopped completely.
Hope this helps.

Yes! This is the exact sound I'm having - loud moaning sound is a perfect description.

Difference here is that my brake on the right isn't quite as strong as the one on the left.
 
Mine did that after new brake pads and fluid flushing during my CI a while back. After 1st flight after CI, I left my wheel pants off so I could check everything after my flight. My right brake groaned like you describe. The only thing different I could see was that since my wheel pants were off, the gear leg fairing had slid down and was pressing against the aluminum brake lines. On the next flight, I still left the pants off put put a piece of aluminum tape on the leg fairings, holding them in place. The brakes didn't groan the next flight. Maybe the fairing pressing against the lines was causing some kind of weird pressure against the calipers or something, resulting in the french horn groan.
This was only one flight and I haven't flown since so I am not 100% sure if this solved my brake groaning or not.
 
I had exactly the same issue on new brakes but it didn't seem to affect brake effectiveness. It was a loud moaning kind of sound, I figured it was the pads dragging slightly.
I lubed the pins, adjusted the brake lines and even put on new disks to no avail.
I was going to put an .040 spacer between the caliper and brake housing, to create a little extra space between the pad and disk but first, I chamfered the edges of the brake pads with a file. Basically putting a small 45 on the edges. After a couple of flights the noise stopped completely.
Hope this helps.

Just how would that work??
 
Holding/not holding during runup is a traditional test of pads that have/have not been properly conditioned. Try one or two firm stops from a modest speed taxi (or whatever your pad manufacturer says), let cool, test again.

Agree. I had the same french horn kind of sound. After doing the conditioning procedure a few times, it was gone.
 
One thing to note. If you get ANY hydraulic fluid on the disc and you don't clean with solvent thoroughly, or if you get fluid on the brake pads, they will also make noise like this. How long depends how much contamination. Lite contamination on the disc will go away quickly, oil directly on the pads can last the life of the pads, getting less noisy as time goes on. It is easy to contaminate the pads if you have the brake line disconnected at the top of the caliper.
 
The plot thickens a bit....

Did a taxi test yesterday...braking action was fine, no moaning. Press down the brakes, set the parking brake, do a run-up...

Once again, the moan starts, nose starts to swing a little left. I can stop it with additional pressure on the right brake, but it feels like I'm going to break the pedal off to hold it.

High speed taxi, no handling or braking problems. Took off, flew, landed, taxied back, took off again, fine.

Shut down at hangar. As I'm pushing the RV back into the hangar, I get the moaning sound again....no braking. And it sounds like it's coming from the left main. I stop pushing, then slowly push it back again and there's the sound again. I stop, rock it gently back and forth. Yup. Moaning sound.

I go to the left wing, put my hand on the left main strut and kind of lean into the wing root to gently push the airplane. Definite moaning sound, and I can feel it coming from the main...the vibration and moan are the same, and it's coming from the gear leg.

So the moan isn't the brake itself, but the brake letting go is causing that moan.

I wonder now if I have two problems....a brake that isn't tight enough and...something else....
 
The plot thickens a bit....

Did a taxi test yesterday...braking action was fine, no moaning. Press down the brakes, set the parking brake, do a run-up...

Once again, the moan starts, nose starts to swing a little left. I can stop it with additional pressure on the right brake, but it feels like I'm going to break the pedal off to hold it.

High speed taxi, no handling or braking problems. Took off, flew, landed, taxied back, took off again, fine.

Shut down at hangar. As I'm pushing the RV back into the hangar, I get the moaning sound again....no braking. And it sounds like it's coming from the left main. I stop pushing, then slowly push it back again and there's the sound again. I stop, rock it gently back and forth. Yup. Moaning sound.

I go to the left wing, put my hand on the left main strut and kind of lean into the wing root to gently push the airplane. Definite moaning sound, and I can feel it coming from the main...the vibration and moan are the same, and it's coming from the gear leg.

So the moan isn't the brake itself, but the brake letting go is causing that moan.

I wonder now if I have two problems....a brake that isn't tight enough and...something else....

The next time this happens, reach in and pull back the top of the right brake pedal on the pilot side... if there is still sound then go pull back on the right pedal on the PASSENGER side. Do the same with the left brake pedals.... One at a time.
 
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The next time this happens, reach in and pull back the top of the right brake pedal on the pilot side... if there is still sound then go pull back on the right pedal on the PASSENGER side. Do the same with the left brake pedals.... One at a time.

I only have brakes on the pilot side, but I'll give this a whirl.
 
The next time this happens, reach in and pull back the top of the right brake pedal on the pilot side... if there is still sound then go pull back on the right pedal on the PASSENGER side. Do the same with the left brake pedals.... One at a time.

So this hasn't happened again. But, because it's good form to post updates...

I ended up having to replace my brake reservoir because I broke it whilst removing the cap which was over-torqued (I seem to struggle with this concept lately) which, of course, required re-bleeding the entire system.

While I was at it, I went ahead and re-lined both brakes. Might as well, right?

So after doing this, the moaning french-horn sound was actually worse. Thinking of this thread, I went through the brake run-in process a couple of times. It diminished some but it's still there. Braking action is good and this time both brakes hold under high RPM, even whilst cycling the prop. So that's good.

I'll keep an eye on this and see what shakes out. Running without the wheel pants for the time being in case I need to do additional MX.
 
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