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Squalling Cleveland Brake

B

Bob Axsom

Well Known Member
In the beginning I had a master cylinder O-ring that was damaged in factory assembly (the O-ring was pinched in assembly and a small crescent was cut out of the edge as it was forced into position). The master cylinder leaked back up through the top and bled on the floor. I bought an overhaul kit and installed the new O-ring and all was fine (after I stretched the return springs to get the piston all the way back when released). Then I allowed the right brake pads to wear down sufficiently to allow the slave cylinder O-ring to clear the cylinder and the fluid bled on that side while parked in Florida. I made a improvised repair with some incorrect pads that were available and flew home. Later when landing at Prescott, AZ the right break line broke at the flare during a short turnoff (lot of pressure I'm sure). I borrowed a flare tool, fixed that and continued on to California the next day. Sometime in this scenario (beginning after Prescott I think but Jeanine says after Panama City) the right brake started making an embarrassing sqaulling noise. I attributed it to brake pad contamination. I tried cleaning and resurfacing the pads and I thought I had it but in fact the intermittent squall upon application of the right brake returned. I thought the pads were saturated so I replaced them but the squalling problem remained. I use the rudder to turn and I tap the brakes when necessary to minimize the squall and I'm getting pretty good at it but the squall remains. This year at annual time I went way overboard and replaced the discs as well as the pads thinking that something may have happened to the right disc during this time. Initially everything was blissfully quiet but yesterday the squall was back. I have some more ideas but I would sure welcome a wise (I mean that in a good way) input or two on this nuisance item.

Bob Axsom
 
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Brake squeal...

gasman said:
Beval the leading eadge of the pad.
Click to expand...

Putting a slight bevel on the leading edge of the pad (about 1/8 inch at 45 degrees) will help. The issue here is a vibration being created in the brake caliper. Another possible fix is to make sure that the bolts/pins that the caliper slides on are clean and rust free. a small amount of a dry lube like graphite helps. If all else fails, a light coat of dry lube on the back side of the pad where it contacts the piston. Obviously being very careful not to get any on the face of the lining or the disc.

John Clark
RV8 N18U "Sunshine"
KSBA
 
Will Do

We are going to Branson in the morning but I will get the fairing off and work this proplem with the recomendations here before next Saturday and I will report the results. One of the fixed recomended by two people involved beveling the leading edge of the pads (the edge facing the incoming rotation of the disc - the bottom) that has a ring of shared experience to it. You might try that while you are waiting - It can't hurt. I will also look for brake fluid seepage around the fitting & piston, spring displacement of the caliper by the aluminum tube, the condition of the guide pins and the piston face and evaluate the need for dry lube.

Bob Axsom
 
squalling brakes

Bob,

A few years ago I replaced the plastic brake lines on my RV-4 with Aluminum tubing all the way to the brake caliper. They both squalled like a son of a gun. Had a nice loop for vibration.

Added a short section of hose into the brake caliper, no more noise.

Chris Murphy

I too went through all of the above mentioned fixes before I did what I knew would fix it.
 
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Bob

I talked to our brake engineer at work today about this. I showed him the plans along with some brake pictures. After I calmed him down about the aluminum tubing being used as a brake line he had a few things to say.

First, try beveling the edge, like a few people have suggested.
Next, use a flexible line to the caliper, again I believe that has been suggested.
Third, change the lining.

Changing the lining will have the biggest potential improvement in brake noise. Brake noise is a big problem in the auto industry and there is always a big battle between chassis, NVH, and quality over the brake linings.

On my next lining change I'll get him to suggest a new lining and I'll test it out. It may be a while sense I changed my lining not too long ago.
 
multiple problems

Bob,
There are several possibilities here. Since the caliper got contaminated you really need to be sure that all the old fluid has been cleaned off, especially from the slider pins. The pins and the aluminum lines are both likely culprits to break squealing. I've got a buddy with an RV-4 who had the same problem.I re-did the lines in ss braided -3 w/teflon liner. I keep this stuff for race cars and bikes I build. He said the brake feel was better and the brake did stop squealing. I never liked the solid line to the caliper, OR the crappy pins in the Cleavland Brakes. Chamfering the leading edges can work, but it is treating the symptom rather than the disease! One of the other things to check is the holes in the caliper backing plates. I have seen some fo the plates that look like the holes were stamped in or drilled by hand using stone tools. If the holes aren't clean and square they tend to skew the pad to the pin twisting the pad a little. I clean them up if needed. That is what chamfering the leading edge helps. It is the pad not staying square that causes the problem though. Good luck
Bill Jepson
 
I have about 50 hours on my RV-7 and have the same problem with the right brake. I have beveled both ends of the pads, bled the brakes several times, deburred and lubed the caliper pins and still can't get it to stop. It only happens during very light braking. I am starting to think that it is possible that the welded flange on the gear leg is not perpedicular to the axle. I plan on checking this soon and possibly swapping the entire brake assemblies from left to right. Let me know if you find a fix.
 
brake lines?

SkywayCaptain said:
I have about 50 hours on my RV-7 and have the same problem with the right brake. I have beveled both ends of the pads, bled the brakes several times, deburred and lubed the caliper pins and still can't get it to stop. It only happens during very light braking. I am starting to think that it is possible that the welded flange on the gear leg is not perpedicular to the axle. I plan on checking this soon and possibly swapping the entire brake assemblies from left to right. Let me know if you find a fix.
Click to expand...

What kind of brake lines do you have?
 
I have solid alum brake lines from the FWF. The left seat lines are flexible AN type. The right seat to left seat lines are plastic.

I am also wondering if the longer run of tubing to the right side is making some sort of difference. It just seems that most people have the problem on the right side.
 
Actual fix

I swapped the brake assemblies left to right and the right side continued to make the "squall". I think that adding flexable line would fix the noise, but I wanted to try one other idea.

I put a very thin layer of high temp silicone on the back side of the inboard pad and this made the noise go away competely.

I hope this helps.
 
More Details Please

I assume the red hi-temp RTV I bought from Aircraft spruce will work. You probable do not have a photo but could you describe exactly where you put the RTV. You said on the back side of the inboard pad, do you mean that literally or do you mean the back side of the metal plate containing the riveted pad?

I'm ready to bite the bullet and add a flexible segment in the line but if this is holding up for you I can do it with little trouble. If it doesn't work for me I can scrape it off and add the flexible line recommended by Chris Murphy.

Bob Axsom
 
I placed the RTV on the metal side of the pad where it contacts the caliper piston. There is a "special" automotive type RTV just for this purpose. It is cheap and you can get it at Napa (National Aviation Parts of America) or Autozone, etc. I would try using that instead of hightemp RTV. I didn't have any of the automotive type on hand so I used what I had. I let the RTV dry before I reassembled the brakes. The idea is that this very thin layer of RTV changes the res. frequency of the pad and provides a bit of cushion.
 
I know exactly what you are talking about

I know exactly what you are talking about - I may even have some in the garage. Thanks for the info.

Bob Axsom
 
Test findings 5-1-08

While I had the fairings off to develop subfairings for racing I inspected the brakes and tried some of the recommended fixes. I found no leaks around the lines or fittings into the slave cylinders. I found a trace of fluid on the face of the piston in the right main gear which I wiped off. I foune wear marks on the guide pins (more on the right than the left). I beveled the leading edge of all four pads. I applied a thin layer of Dow 736 hi-temp RTV to the back of the plates containing the inboard pads in the piston area only. I cleaned and lubed the guide pins.

Test - One flight around the pattern before refueling for tomorrow's flight to Abilene. The brakes seemed a little softer possibly because of the rubber (RTV) and they still squal though perhaps not as much.

Bob Axsom
 
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Bummer. My squall is still gone, but I did notice that my master cylinders were not always realeasing completely. I put some aux springs on them as posted elsewhere.

I think that I am going to add a section of flexable line to mine anyway. I just figure that the silicone is a bandaid.
 
Things are looking up

With no further changes we flew to Abilene, Texas, had to land at the civilian airport because the Air Force Base was not accepting civilian arrivals until 11:30, landed at Dyess Air Force Base taxied a couple of miles to the overnight hangar, taxied in the morning to the show plane display area, taxied to the far end of the runway for the race launch, landed at Graham, Texas to refuel on the way home, landed at Drake Field in Fayetteville, Arkansas and taxied to the hangar, all without one squall from the brakes. Something in the changes made is having a a good effect.

Bob Axsom
 
Any more Squealing Brakes???

I have an -8A and it sounds bad when I do any light braking.

From reading this thread, RTV on the pad facing the piston is the fix, as well as cleaning and lubing (which i've tried before to no avail).

Any ideas are welcome! :confused:
 
I am parked outside and on the cold I noticed a screeching sound after I start moving and during first couple turns. After pads heat up the squeal stops. I attribute it to thermal contraction/expansion and uneven heating. Might be your case as well.

squeal%20-%201.jpg
 
Rotorheadrob said:
Any more Squealing Brakes???

I have an -8A and it sounds bad when I do any light braking.

From reading this thread, RTV on the pad facing the piston is the fix, as well as cleaning and lubing (which i've tried before to no avail).

Any ideas are welcome! :confused:
Click to expand...

Hi Rob, Did you try beveling the leading edge of the pad. Are you still in Medford?
 
Solved my RV-8 Brake noise finally

After trying ALL of the forum suggestions on my RV-8 brakes, I finally hit upon the solution that solved it completely for me. I did really try everything I could read about that helped any other plane.

I replaced the tires on my Cherokee over the winter and found that the wheel nuts were VERY much tighter than I normally install these on my RV.

When I did my annual, I tightened the wheel nuts a flat tighter than I normally would and installed the cotter pin.

Brake noise GONE!

I still flinch when I brake - but no noise. I guess it will take a while to stop doing that :)
 
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