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  #1  
Old 07-21-2022, 10:05 PM
Paul Eastham's Avatar
Paul Eastham Paul Eastham is offline
 
Join Date: Oct 2005
Posts: 516
Default A symphony of brake squeaks

Was surprised not too see many posts in the archives about that match this, curious if there is some collective wisdom. I wish I could just take the whole thing apart and give some actual data, but I just left home for OSH, of course

Brake was squeaking a little at annual, so I gave it a good look. Found the rotor was a bit out of tolerance (had a slight low spot and was slightly too thin). Replaced the rotor, should have changed the pad but didn't, had plenty of life left. On flying it, a tiny bit of squeak remained over a dozen flights but it was very tolerable.

Now I hit the road and landed at my first overnight and it squeaks again...LOUD! It sounds like someone threw a bunch of metal shavings into the brake. This was with light pressure as I was parking, braking action was fine and the brake was not hot.

I guess I will voyage on tomorrow morning and hope for the best...
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  #2  
Old 07-22-2022, 07:34 AM
D Weisgerber's Avatar
D Weisgerber D Weisgerber is offline
 
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Location: Ionia Michigan
Posts: 386
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Do you have Cleveland or Matco brakes?
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  #3  
Old 07-22-2022, 07:56 AM
TS Flightlines TS Flightlines is offline
 
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Location: Ridgeland, SC
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Typically, one or the other has some glaze on the surface. Pull the pads, scuff the surface, same for the rotors, then bed the pads during a taxi-braking procedure. "usually" fixes it.
Tom
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  #4  
Old 07-22-2022, 08:06 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 7,730
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Quote:
Originally Posted by Paul Eastham View Post
Was surprised not too see many posts in the archives about that match this, curious if there is some collective wisdom. I wish I could just take the whole thing apart and give some actual data, but I just left home for OSH, of course

Brake was squeaking a little at annual, so I gave it a good look. Found the rotor was a bit out of tolerance (had a slight low spot and was slightly too thin). Replaced the rotor, should have changed the pad but didn't, had plenty of life left. On flying it, a tiny bit of squeak remained over a dozen flights but it was very tolerable.

Now I hit the road and landed at my first overnight and it squeaks again...LOUD! It sounds like someone threw a bunch of metal shavings into the brake. This was with light pressure as I was parking, braking action was fine and the brake was not hot.

I guess I will voyage on tomorrow morning and hope for the best...
Installing a new rotor with old pads is frowned upon in the auto world and expect the same for aviation. Rotors develop countless grooves and the pads wear into a shape that matches them. You put on a nice flat rotor and now you have a bunch of small contact patches (pads have a contour matching the old, worn rotor) and made no effort to form the pads to the new rotor, so not surprising it is squealing. Try several aggressive, heavy braking maneuvers, allowing cooling between them (our RVs can't handle the brake heat that our cars can). This is a necessary step any time a rotor is changed. The process generates a lot of heat and transfers compounds from the pads to the rotor surface, creating a protective glaze. It will also help wear the pad back into a shape that matches the rotor.

Larry
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Last edited by lr172 : 07-22-2022 at 08:22 AM.
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  #5  
Old 07-22-2022, 08:11 AM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Quote:
Originally Posted by TS Flightlines View Post
Typically, one or the other has some glaze on the surface. Pull the pads, scuff the surface, same for the rotors, then bed the pads during a taxi-braking procedure. "usually" fixes it.
Tom
The process of bedding in new pads and rotors is actually designed to put a chemical glaze on the rotor. This helps the rotors to minimize rusting and grab the pads better. It takes intense heat to get the compounds in the pad to transfer to the metal rotor and hence the very aggressive braking involved in this process.

That said, I agree that sometimes oils or other undesired elements end up on the pads, creating interface problems and they should always be cleaned with brake cleaner before installing. A rotor is almost universally coated with oils to protect them from rust while sitting on the shelf. If the OP did not clean the rotor with brake cleaner before installation, then yes, both pads and rotors are contaminated and should be cleaned and sanded before the bedding process. If this was done, it may take several rounds of acetone or similar to get the oils out of the pads. An old trick is to soak that pad in gasoline for 30 minutes and then heat with a propane torch to burn out the thinned oil.

Larry
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Last edited by lr172 : 07-22-2022 at 08:32 AM.
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  #6  
Old 07-22-2022, 02:43 PM
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Paul Eastham Paul Eastham is offline
 
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Thanks all for your thoughts. Today it was somewhat better, still not good. But at least it is functioning properly, hopefully enough for a dozen more landings and taxiing around OSH :O
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  #7  
Old 07-22-2022, 05:00 PM
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RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by lr172 View Post
An old trick is to soak that pad in gasoline for 30 minutes and then heat with a propane torch to burn out the thinned oil.
Well, *this* sounds safe LOL!

I'm sure it's fine, it just sounds like an accident waiting to happen, at least if *I* did it.
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  #8  
Old 07-23-2022, 11:13 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by RV7A Flyer View Post
Well, *this* sounds safe LOL!

I'm sure it's fine, it just sounds like an accident waiting to happen, at least if *I* did it.
Kind of assumed the risk would be somewhat obvious. If you do it in an open area on concrete surface, it is a non event. It doesn't explode or anything. Un compressed gasoline is just like lighter fluid; Very tame burn characteristics in small quantities. Mix with air and compress it, like our engines do, and it is an entirely different animal.

Larry
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Last edited by lr172 : 07-23-2022 at 11:17 AM.
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  #9  
Old 07-31-2022, 10:32 AM
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Paul Eastham Paul Eastham is offline
 
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To close the loop on this thread, upon disassembly I found a small crack on the face of the pad, right up against the outer edge. It looked very superficial, and nowhere near the rivets so it didn't look scary or like the pad was about to fail. But with my thumbnail I was able to break off the edge of the pad at the crack.

I guess that crack was enough to contaminate the larger surface with bits of dust and metal, causing all the racket.

Upon replacement all is back to normal. (I also cleaned everything with brake cleaner, and beveled the new pads)
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EAA Chapter 338 San Jose

Last edited by Paul Eastham : 07-31-2022 at 10:34 AM.
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