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  #1  
Old 09-21-2019, 12:05 PM
WingnutWick's Avatar
WingnutWick WingnutWick is offline
 
Join Date: Jun 2013
Location: Fresno, CA (KFCH)
Posts: 272
Default Horrible brake noise with new brakes/lines!

Hello!

So following my girlfriend's brake fire on her 6A I replaced the tire, tube, pads, and put on a braided nylon line instead of the previous rigid line. I cleaned the brake assembly as well and replaced the O-ring. The rotor was new just prior to the fire so I kept it. It had darkened from the fire which I though would clean off after a few uses of the brakes. I also used the opportunity to swap the bleeder valve from the top to the bottom.

After the repair all seemed normal vice a small pulsing in the right brake which I attributed to warping of the disk from the fire. Then after a couple flights a groaning sound began occurring during brake application which got progressively and rapidly worse.

I decided to replace the rotor altogether. I did this and initial taxi test seemed to solve the problem. The next time we went to fly, the noise was there with brake application and again, again getting progressively worse. I looked at the pads and there was some darkening that I figured was residue from the old, burned rotor. So then I replaced the pads today with new ones thinking that they had been contaminated by the old rotor.

Figuring I had the problem licked, my initial first brake attempts had no sound, then to my dismay, about 5 minuted into taxi test it came back again!
Now I am lost. I've re-done brakes a bunch of times on RV's with never an issue. I'm guessing the reason the sound doesn't start right off the bat after replacing thee items is due to the fact the pads were still new and not really gripping yet. But I still can't figure out what the heck is causing this horrible sound. The left has the old rigid brake line, the right brake (the repaired one making the sound) has the new flexible braided one.

My suspicions at the moment:
1. Due to event small amount of potential residue which remains from the original rotor? - Seems unlikely.
2. Due to swapping out the valve to the bottom?
3. Due to the new braided line somehow?
4. Some warping or compromise of the entire brake assembly due to the fire?

Here is a video so you can hear the sound which reverberates through the entire plane is quite unbearable. And photos of both brakes. As always, your help and insight is priceless!

VIDEO: https://youtu.be/lZGOIEUarts


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Last edited by WingnutWick : 09-23-2019 at 11:07 PM.
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  #2  
Old 09-21-2019, 12:34 PM
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Pmerems Pmerems is offline
 
Join Date: Jan 2006
Location: Tucson, AZ
Posts: 828
Default Low frequency

Sounds like a low frequency vibration. Is the recording with the wheel pant on? If so the low frequency maybe amplified by the wheel pant. Also the gear fearing maybe channeling the noise up through the fuselage. Maybe the fire effected the wheel pant bracket material properties and is now resonating with any break/rotor interactions.

Please post a solution when resolved. Best of luck.
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  #3  
Old 09-21-2019, 12:47 PM
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Bill Boyd Bill Boyd is offline
 
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Location: Landing field "12VA"
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Default

If it's any consolation, my 6A right brake has made that noise from day one, and it's persisted through brake pad replacement and brake bleeding. 21 years and 970 hours later, still there. Mine is not as persistent, only present when nearly stopped, but you can hear it from quite a distance.

I, too, would like to know how to eliminate it, but consider it a "cosmetic" rather than functional issue. IOW, as embarrassing as it is on the tarmac, I've learned to shrug it off and live with it.
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  #4  
Old 09-21-2019, 02:39 PM
Johnnybgoode Johnnybgoode is offline
 
Join Date: Dec 2012
Location: NC
Posts: 112
Default

Try switching the bleeder valve back and see if it goes away. Just a thought.
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  #5  
Old 09-21-2019, 03:34 PM
dreed dreed is offline
 
Join Date: Nov 2016
Location: Camas, WA
Posts: 506
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OK, I may be showing my RV ignorance here (still building), but why would you put the bleeder on the bottom? Are you just cracking the lines at the to bleed now vs using the bleed screw? You can't bleed it from the screw on the bottom unless there is some trick I don't know or haven't learned/read about yet. Could it be the air in the caliper causing some cavitation/vibration.

I saw this firsthand on a car once when someone installed calipers on a 911 upside down (Left caliper on right side of car and ice versa). For the life of them couldn't figure out why they couldn't get all the air out of the brakes after numerous attempts to bleed. Then one of us noticed what what going on and pointed out his mistake and that air likes to go up in the calipers. Quick swap and everything worked out great.
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Last edited by dreed : 09-21-2019 at 03:42 PM.
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  #6  
Old 09-21-2019, 03:55 PM
Ron77 Ron77 is offline
 
Join Date: Jul 2017
Location: Kemah, Texas
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I recently overhauled my brakes and upgraded the lines to SS braided teflon hose, like yours. After the brake work, I also experienced brake chatter and chased my tail for quite some time trying to solve the issue. Finally, out of desperation, I changed the brake lines back to aluminum line and the chatter disappeared. Don’t ask me why.....

Dan, most RV guys bleed brakes by pushing fluid from the calipers up to the master cylinders, hence the bleeder installed on the bottom.

Ron B
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  #7  
Old 09-21-2019, 04:41 PM
dreed dreed is offline
 
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Location: Camas, WA
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Ahh... makes sense. Thanks Ron!
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  #8  
Old 09-21-2019, 06:14 PM
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RV6_flyer RV6_flyer is offline
 
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Location: NC25
Posts: 3,763
Default

If you search the Matroinics RV-list, you will find around 20-years ago, people that tried to use hose had brake noise issues. If the rigid aluminum lines was not perfect aligned, it would also create the same noise you posted to YouTube just like most people that attempted to use hose had.

When you pressurize the brake line, the caliper moves to an angle that makes noise.

The bleeder is suppose to be on the bottom. This allows a pressure pot to be used to force brake fluid up to the master cylinder reservoir. This should then give you a brake system with no air in the lines.
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  #9  
Old 09-21-2019, 06:28 PM
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Pmerems Pmerems is offline
 
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Location: Tucson, AZ
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Default Flex line do work without noise.

Flex lines for 9 yrs and counting. No noise.
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ExperimentalAero-HANGAR BANNERS
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  #10  
Old 09-21-2019, 08:13 PM
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Steve Melton Steve Melton is offline
 
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Location: Cincinnati, OH
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I have flex lines and no noise. these are special lines using -3 hose with -4 fittings. there is some thought that -4 flex lines are too flexible and cause a hydraulic resonance. smaller diameter flex lines are stiffer diametrically. what size is your flex line?
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