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30-9 brake question

LarryT

Well Known Member
Where can I find dimensional information to inspect a 30-9 Cleveland brake assembly?

I was unable to find any dimensional information such as wear limits etc. on the Parker Hannefin website. I contacted them by e-mail, they stated I would get a response in two days. It has been two weeks and no response.

It seems like this information would be publicly available so A&P mechanics can inspect the components to insure airworthiness.

Larry Tompkins
544WB -6A
W52 Battle Ground, WA
 
bump on brake question

Is there really no one with any info? Do you A&Ps just slap a new o-ring in without measuring anything?

Sometimes being an engineer is a real curse.

LarryT
 
Brakes

The pucks do not wear , no metal to metal contact . What kills them is corrosion , pits in the caliper and puck . Put a new oring on it every now and then and don't over think it ,( just kiding on the over thinking ).
Tom
 
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Excessive clearance

What if they were out-of-spec to begin with? I measured .010" piston to bore clearance. That can't be correct for a nominal 1.5" diameter. Should be more like .003".

If they didn't wear, then either the piston was originally machined undersize or the bore was machined oversize. Without dimensional information, what do you suggest I do beside slap a new o-ring in it and have it extrude again?

Perhaps I won't be lucky enough to have it happen on the run-up next time. If you saw my home airstrip, with trees and ditches on both sides of the runway, you would probably not want to have a brake failure on landing there either. And yes, i do try to land with as little speed as possible so I don't need to brake. In my opinion that technique does not replace trying to fix the problem.

Larry
 
Brakes

I'm surprised you did not get an answer from the manufacturer . Did you measure both caliper bores and pucks ? Are they the same ? Proper O ring ?
I have a new one , never used , I will measure it today .
Tom
 
Brake

Was the puck ( piston ) installed in the proper direction ? If not the oring will come out when the pads are worn .
Tom
 
What if they were out-of-spec to begin with? I measured .010" piston to bore clearance. That can't be correct for a nominal 1.5" diameter. Should be more like .003".
Without dimensional information, what do you suggest I do beside slap a new o-ring in it and have it extrude again?

Consider coefficient of thermal expansion. Anyway, it's hard to believe a caliper o-ring can extrude through a 0.010" clearance.
 
The steel lining plate sits right on the aluminum piston and the piston immediately catches the heat from the linings. I'd better with only .003 clearance it would lock right up. Some pistons have an insulating disc on top. These don't.
 
thanks for posts.

Here is some background info: 1. Caliper failed hydraulically during run-up at Buchanan Field, Concord, CA 2. Repairs by Sterling Aviation 3. O-ring was found to be partially extruded/damaged. 4. No measurements of piston or caliper bore were taken 5. Repair consisted of o-ring replacement and pressure testing by brake application in the aircraft.

I have two brake assemblies that I purchased from a VAF member sitting on the shelf. I disassembled one to take measurements. Part of my interest was to see if I could replace the circular section o-rings with square section o-rings, which are used in 100% of automotive brake applications today. Assisting me was the supervisor of a machine shop that specializes in the repair of hydraulic cylinders. Using his equipment, we measured the piston to bore clearance at .010 by measuring piston OD and bore ID. From our experience, this struck both of us as excessive clearance. Not wishing to rely on either his or my assumptions, I contacted Parker-Hannefin and requested dimensional information for the two components I was promised a response and have heard nothing for three weeks.

FWIW, numerous posters on this website have had similar failures and recommend packing spare o-rings

Here are answers to posts by #

#5 &6 I was surprised, too. However, despite my written explanation that the information was requested to inspect components on my own aircraft, I did send the e-mail from my work computer, which identifies me as a forensic engineer. Yes, the piston was correctly installed.

#7 I previously looked at the maintenance and the service manuals. There is plenty of info re bolt torques, lining thickness and rotor thickness. Unless I missed it during several reviews, there is no dimensional info re piston OD and caliper bore ID.

#8 Dan, both the piston and caliper are aluminum. Heat path into the piston is from the inside backing plate and heat into the caliper is from the outside backing plate. I was a Sr. Brake Engineer at Kelsey-Hayes. All new designs were tested to hydraulic failure with a minimum factor of safety of 4x the maximum in car working pressure. My 48mm piston diameter brake had .004 -.007 clearance because it had a phenolic piston. For a metal piston, the clearance would have been .003 - .005. My brake was tested at the .007 upper clearance limit. Failure was at 9200 psi. Failure mode was partial extrusion of the square cut o-ring. The 30-9 caliper uses a circular section o-ring. The auto industry switched from circular section 0-rings to square cut o-rings decades ago.

My own personal interest in this investigation is to determine whether a square-cut o-ring would be a better choice in this application, but it is hard for me to do any testing until I am knowledgable about the design intent of piston - bore clearance.

Larry
 
Here is some background info: 1. Caliper failed hydraulically during run-up at Buchanan Field, Concord, CA 2. Repairs by Sterling Aviation 3. O-ring was found to be partially extruded/damaged. 4. No measurements of piston or caliper bore were taken 5. Repair consisted of o-ring replacement and pressure testing by brake application in the aircraft.

I have two brake assemblies that I purchased from a VAF member sitting on the shelf. I disassembled one to take measurements. Part of my interest was to see if I could replace the circular section o-rings with square section o-rings, which are used in 100% of automotive brake applications today. Assisting me was the supervisor of a machine shop that specializes in the repair of hydraulic cylinders. Using his equipment, we measured the piston to bore clearance at .010 by measuring piston OD and bore ID. From our experience, this struck both of us as excessive clearance. Not wishing to rely on either his or my assumptions, I contacted Parker-Hannefin and requested dimensional information for the two components I was promised a response and have heard nothing for three weeks.

FWIW, numerous posters on this website have had similar failures and recommend packing spare o-rings

Here are answers to posts by #

#5 &6 I was surprised, too. However, despite my written explanation that the information was requested to inspect components on my own aircraft, I did send the e-mail from my work computer, which identifies me as a forensic engineer. Yes, the piston was correctly installed.

#7 I previously looked at the maintenance and the service manuals. There is plenty of info re bolt torques, lining thickness and rotor thickness. Unless I missed it during several reviews, there is no dimensional info re piston OD and caliper bore ID.

#8 Dan, both the piston and caliper are aluminum. Heat path into the piston is from the inside backing plate and heat into the caliper is from the outside backing plate. I was a Sr. Brake Engineer at Kelsey-Hayes. All new designs were tested to hydraulic failure with a minimum factor of safety of 4x the maximum in car working pressure. My 48mm piston diameter brake had .004 -.007 clearance because it had a phenolic piston. For a metal piston, the clearance would have been .003 - .005. My brake was tested at the .007 upper clearance limit. Failure was at 9200 psi. Failure mode was partial extrusion of the square cut o-ring. The 30-9 caliper uses a circular section o-ring. The auto industry switched from circular section 0-rings to square cut o-rings decades ago.

My own personal interest in this investigation is to determine whether a square-cut o-ring would be a better choice in this application, but it is hard for me to do any testing until I am knowledgable about the design intent of piston - bore clearance.

Larry

We have upgraded Pucks and Viton orings in stock.
 
Here is some background info: 1. Caliper failed hydraulically during run-up at Buchanan Field, Concord, CA 2. Repairs by Sterling Aviation 3. O-ring was found to be partially extruded/damaged. 4. No measurements of piston or caliper bore were taken 5. Repair consisted of o-ring replacement and pressure testing by brake application in the aircraft.

Larry, please excuse, but I must ask...

The above was your airplane, and you examined the failed o-rings yourself?

FWIW, numerous posters on this website have had similar failures and recommend packing spare o-rings

Yes, overheated nitrile o-rings leak. It's easy to overheat them as our little bitty brakes are only rated at 117,500 ft-lbs kinetic.

#8 Dan, both the piston and caliper are aluminum. Heat path into the piston is from the inside backing plate and heat into the caliper is from the outside backing plate. I was a Sr. Brake Engineer at Kelsey-Hayes.

I appreciate your experience. I'm sure you know it would only take a temperature differential of 154F to lock the piston given a clearance of 0.003". I was thinking it might be possible for the temperature of the very low-mass aircraft piston to spike upward 154F before heat could conduct all the way around the back of the caliper, and then warm the large caliper mass and enclosed fluid. I could be wrong of course.

My brake was tested at the .007 upper clearance limit. Failure was at 9200 psi. Failure mode was partial extrusion of the square cut o-ring. The 30-9 caliper uses a circular section o-ring.

FAR 23.397 specifies maximum control force inputs. It lists 200 lbs for a rudder, but does not specify for a brake input. Let's be generous and assume a determined pilot might push 100 lbs with the toes of one foot (i.e. a full 200 lbs on the pedals for a runup), and does so at the very top edge of the pedal. The pedal ratio (for an -8 or 8A) would then be 5 / 1.75 = 2.85. The master cylinder piston is 0.5625"D, thus area is .2484 sq in. So, (2.85 x 100) / .2484 = 1147 psi, a long way from 9200.

Here's a nice little chart from the Parker O-Ring Handbook:

Extrusion%20Limits.jpg


Given Shore 75 elastomer, it seems to suggest that 0.010" clearance is a reasonable design limit for 1000 psi.
 
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Consider coefficient of thermal expansion. Anyway, it's hard to believe a caliper o-ring can extrude through a 0.010" clearance.

The o-ring can extrude, but typically that is a typically a design issue. My experience, with millions of o-rings per year installed in fuel injectors, is an installation cut. (a very dynamic application) I am not passing judgement here as the OP seems to have experience with these failure modes, but again, while an extrusion failure with .010 clearance is possible it is also unlikely.
 
Reply to post #14 and others

Dan: yes my airplane. I did not disassemble (that was Sterling Aviation), but yes, I examined the o-ring. It was abraded in one area, not around the entire circumference. It was not cut in two.

Re clearance and expansion, please see post #12. reported new caliper/piston clearance was .002. Thank you gz for taking the time to measure your new brake and report.

Bill L: I would not expect to see o-ring extrusion at the line pressures we run either. The brake is rated at 450 psi and Parker says to test at 600 psi.

Larry
 
Re clearance and expansion, please see post #12. reported new caliper/piston clearance was .002.

Saw that, but you reported 0.010" for a different caliper. Let's hope Parker will supply bore and piston specifications. Let us know.

Why not pull and measure the failed caliper if you have concerns? I'm pulling mine down for a viton o-ring transplant during the annual next month...I'll get numbers.

I would not expect to see o-ring extrusion at the line pressures we run either. The brake is rated at 450 psi and Parker says to test at 600 psi.

At 600 psi, Fig 3-2 suggests the clearance limit could be as much as 0.017" with a shore 75 ring.

Darned interesting.
 
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Dan: yes my airplane. I did not disassemble (that was Sterling Aviation), but yes, I examined the o-ring. It was abraded in one area, not around the entire circumference. It was not cut in two.

Re clearance and expansion, please see post #12. reported new caliper/piston clearance was .002. Thank you gz for taking the time to measure your new brake and report.

Bill L: I would not expect to see o-ring extrusion at the line pressures we run either. The brake is rated at 450 psi and Parker says to test at 600 psi.

Larry

Larry,

Has the o-ring lip peeled back (lifted) on your puck?



It will end up breaking as in this pic.
 
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Reply to #17 & 18

I intend to disassemble all 4 calipers I have this winter. Flying season is almost over here in the NW.

Dan: I think your calculation using 100 lbs. application force is conservatively high. The FMVSS 105 Brake Standard that vehicles have to comply with allows a maximum pedal application force of 120 Lbs. I don't think the RV seating position would result in anything like that. FWIW, I thought I was only applying enough force to hold the aircraft during the run-up. I also don't think I brake hard or drag the brakes. Perhaps my perception is incorrect.

Is my understanding correct that you think heat and nitrile O-rings is the issue, and that changing to Viton O-rings is the solution? Am I wasting my time contemplating testing of square section O-rings (I would use Viton ones as I do agree that is an improvement)? FWIW, the auto industry hasn't used circular section O-rings since the 4-piston fixed-caliper brakes on late '60s Mustangs.

Parker has not responded in the time frame they said they would, despite my honest and correct representation that the information was for inspection of my own personal aircraft brakes to service limits.

Reiley: I examined the lip on the puck as I noted there isn't much edge margin from the groove to the backside of the piston. It appeared to be OK to me and also to the mechanics at Sterling Aviation.

For anyone who has been following this thread: if you have a damaged 30-9 brake caliper that is still hydraulically sound, e.g., a broken mounting ear or something like that, I will gladly pay the shipping cost for you to donate it for test purposes.

I would like to have some calipers that I can test to destruction. I will gladly post the results on this forum - even if I embarrass myself. A wonderful old British engineer who reported to me once stated: "one test is worth a thousand opinions." I heartily subscribe to that philosophy if the test is conducted with protocol in accordance with the Scientific Method.

Thank all of you very much for your contributions to this discussion.

Larry
 
Is my understanding correct that you think heat and nitrile O-rings is the issue, and that changing to Viton O-rings is the solution? Am I wasting my time contemplating testing of square section O-rings (I would use Viton ones as I do agree that is an improvement)?

Baked-to-failure has been the common issue with nitrile seals.

Don't know anything significant about square section rings.

If I had an A-model and used the brakes to steer much I'd swap the rotors using a Cleveland 199-93 kit. The kinetic rating jumps from 117,500 to 155,000. I've done one such conversion and liked the result very much.

"one test is worth a thousand opinions."

Absolutely.
 
Dan: I think your calculation using 100 lbs. application force is conservatively high. The FMVSS 105 Brake Standard that vehicles have to comply with allows a maximum pedal application force of 120 Lbs. I don't think the RV seating position would result in anything like that.

I may be missing something here, but I think that most of us could easily generate forces well in excess of that.

A 200 pound pilot is applying 100 pounds per leg just to stand up, and I'd guess most of us could stand up with someone our size on our shoulders while standing.

The geometry of a squat isn't much different than the geometry of applying brakes in my RV-8.
 
Bump...tell us why.

1) Heat
2) Pressures
3) And most important the o-ring lip at the land. The material is to thin. Notice the puck is distorted all the way around the land on the face of the puck... till it gives up. (the distortion cracks)
New pucks have a flat smooth surface.

One other thing I might add is that after about 5/8 wear in the pads, you will find the puck face does not stay parallel with the caliper housing. it will be cocked off to one side. This might just be causing the "peeling back" of the distorted landing face. If you look closely, the puck does not rotate in the caliper housing much if at all during the wear session of a set of brake pads.
 
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1) Heat 2) Pressures 3) And most important the o-ring lip at the land. The material is to thin. Notice the puck is distorted all the way around the land on the face of the puck... till it gives up. (the distortion cracks)

None would strip the thin edge off the land, as there is no unbalanced pressure applied to it by brake application.

Consider the following, again from the Parker O-Ring Handbook:

Parker%20Text.jpg

Parker%20Extrusion%20Illustration.jpg
 
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They're all related, but no matter. None would strip the thin edge off the land, as there is no pressure applied to it by brake application.

Consider the following, again from the Parker O-Ring Handbook:

10q9t9c.jpg

2lwm55k.jpg

there is pressure on the lip when brakes are applied by the oring itself. This is not a one time issue, it has been found on many RV's. Its funny that none have had the same failure with the upgraded pucks. I'll be done here. :)

I take that beautiful deformed ring around the land was an act of God. No, it was the oring.
 
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there is pressure on the lip when brakes are applied by the oring itself.

The pressure on the lip due to pedal application is equal and opposite on both its faces.

Consider the sketch.

(A) is an idealized representation. A high pressure area and a low pressure area are separated by the o-ring. High pressure forces the o-ring toward the low pressure, against the narrow annulus and away from the lip. Fluid pressure is the same on both sides of the aluminum lip.

(B) is a more refined representation. The o-ring fills the entire groove. The o-ring is still forced toward and into the low pressure annulus. The pressure within the o-ring itself (which the Parker Handbook describes as "an incompressible viscous fluid") is the same as the fluid pressure. Pressures on each side of the lip are functionally identical.

Caliper%20Sketch.jpg


This is not a one time issue, it has been found on many RV's.

Perhaps you could quantify "many", after which we can look for the real cause.

POSTSCRIPT: Many mechanics remove the piston from the caliper using compressed air. If the piston is allowed to come out crooked, it can catch and break the lip. Use very low pressure and make sure the piston comes out straight.
 
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brakes

LarryT,
I have a book that i use for dimensional tolerance. Have had it for years, I think it is by Cleveland. It gives rotor min thickness, brake pad cross references, torques and everything you need to know for servicing brakes. I think I got it at one of the IA seminars as a free pickup. Check your local parts dealer, they should be able to get you one.
Jim
49clipper
RV-6 AP/IA/cfi
 
Response to #31

Jim would you please look in your service book t o see if you can find:

1. Caliper bore diameter. Maximum diameter allowed.

2. Caliper Piston OD. Minimum diameter allowed

3. If there is any recommendation for minimum and maximum piston to bore diametral clearance, which is obviously the difference between the caliper bore ID and the piston OD.

You could very well have a Parker Cleveland brake book of which I am not aware. However, I have looked over the current information available on the Parker website, and I do not find any of the 3 items above published.

Larry
 
The problem you have is the caliper housing is NOT in tolerance Period NEW! The pucks are NOT even in tolerance Period NEW. Measure this #*&^ out. Parker knows about this issue and has been addressed face to face, they elect to not discuss the issue. Fly on....
 
Looks to me like Dan needs to get off his @&& and figure this one out. He has the KNOWLEDGE. :)
 
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The problem you have is the caliper housing is NOT in tolerance Period NEW! The pucks are NOT even in tolerance Period NEW. Measure this #*&^ out. Parker knows about this issue and has been addressed face to face, they elect to not discuss the issue. Fly on....

Larry has been asking for bore/piston dimension and tolerance since the first post of this thread. Apparently you know them, as without them you would have no basis to criticize Parker's manufacturing quality. Would you be so kind as to share?
 
Thank you, Dan

I thought it was a pretty simple question. If Parker was willing to give me the answer, I wouldn't have bothered anyone on this Forum with this question at all.

FWIW, I was merely trying to rule out that any dimensions were outside of Parker's design intent. If Parker can't make them to their own design tolerances, that is a completely different issue. It is easy enough for me to get pistons turned to the correct dimension. Unless the caliper bore is undersize, caliper bore correction would be more difficult. If the caliper bore is oversize, there are two choices: a) replace the caliper, or b) machine a slightly oversize piston to maintain proper clearance.

At this point, in light of the graph Dan provided (thank you very much), I am inclined to think that at our low operating pressures , the issues are most probably baking of the o-ring or the brake puck was reversed. As I did not disassemble the offending brake, I cannot be certain how the puck was installed.

Because I am operating in the absence of information that ought to be public domain, but isn't being shared, I will overhaul all of the four calipers I presently own. I will report back on this site the dimensional information for each of the four calipers. I may swap pucks between brake calipers to maintain the most appropriate clearances. I will rebuild each caliper with Viton O-rings.

Unless you are the possessor of the information I requested in post #1, I don't think there needs to be any further discussion until I report back.

Thank you all for your contributions to the discussion.

Larry
 
Here is the rest of my brake story

One sunny day about a week and a half ago, I went to my hangar intending to fly. Opened the door and there was a puddle of red 5606 under the left wheel. This was the caliper that was rebuilt at KCCR. I had literally made only 6 landings since the caliper was "repaired." One of them was a touch and go and one I had to add power to make the first turn off at Scappoose.

It was distressing to say the least. I removed the caliper and removed the piston. It had been reinstalled BACKWARDS! While that was upsetting, after a while, the thought occurred to me - maybe they put the piston back in reversed because that is the way it came out.

Therefore, I determined to remove the right brake caliper for disassembly. Yes indeed, the piston in the right caliper was also reversed.

I have now precisely measured all 4 calipers and pistons. Here are the results:

1. All four caliper bores measured within a couple ten thousandths of 1.500
2. Both pistons from brakes removed from the aircraft measured 1.495
3. One spare piston measured 1.496; the other measured 1.490
Based on the Parker chart supplied by Dan H. in a previous post, all of these clearances are acceptable for resistance to seal extrusion.

Here are some other observations/conclusions:

1. The nitrile o-ring that came out of the right brake showed no
sign of heat damage, which I believe confirms my perception that I try to fly competently, control my speed on final and touch down relatively slow - most of the time, anyway.

2. Both brakes most probably had the pistons installed backwards when I purchased it. It is not possible to say when this occurred, as the linings only recently had enough wear for the hydraulic failure to occur.

3. Shouldn't an A&P know which way the piston goes in?

4. Should I have hovered over the mechanic while he was disassembling the offending brake when we were AOG at KCCR? There were signs telling unauthorized personnel to stay out of the shop.

Here is the final bottom line

1. No one was hurt; no airplane was bent
2. I will be reassembling the brakes with Viton O-rings
3. While I am of the opinion that the existing Cleveland 30-9 is not state of the art, with the addition of Viton O-rings, it is my opinion that the brakes will be adequate for the way I taxi and land the aircraft.

Once again, I want to thank everyone profusely who followed and participated in this discussion. I received many helpful suggestions. Perhaps I should have listened to the poster who suggested the pistons were reversed in the first place - but I just couldn't bring myself to believe that an A&P wouldn't notice upon disassembly that the piston was reversed and that he would repeat the problem.

Larry Tompkins
-544WB -6A
W52 Battle Ground WA
 
Blew an o ring yesterday on emergency landing. 5606 smoked a lot but did not ignite. Glad for that. Reading all this has me pretty cautious. Going to Google Viton and see where to order Monday. The remaining question is, which way does the puck face? Can anyone supply a pic or drawing or just describe it for a mechanical idiot? Thanks very much in advance.
 
Blew an o ring yesterday on emergency landing. 5606 smoked a lot but did not ignite. Glad for that. Reading all this has me pretty cautious. Going to Google Viton and see where to order Monday. The remaining question is, which way does the puck face? Can anyone supply a pic or drawing or just describe it for a mechanical idiot? Thanks very much in advance.


The GROOVE on the PUCK goes into the caliper first.

From Rosie: See this thread for more discussion.

brake_puck.jpg
 
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Gary's photo...

...indeed shows the correct installation. Unless there is too much clearance between the piston and bore, it is unlikely that an o-ring will extrude at the system pressure we use until the brake lining material is pretty well used up. If the pistons are installed reversed, o-ring extrusion willoccur when the brake linings are approximately 50% worn.

I would encourage anyway who finds a piston reversed on one side to pull the other brake caliper. My home airstrip's runway goes over a culvert at mid-field. There are ditches on either side of a 42' wide runway. I would not like to lose a brake on an aircraft with a free-castering nose wheel on landing. Thankfully for me, my first extrusion occurred during the run-up prior to take-off, which is perhaps a good argument to apply the brakes harder during the run-up than you apply them upon landing. The second extrusion (on the same brake, see my previous post) apparently occurred during the end of my 6th landing after the "repair."(not performed by me), but also thankfully did not exhaust all of the brake fluid. I had brakes all the way back to the hangar, but in retrospect, I noticed the "repaired" brake felt soft. That brake continued to leak on the floor of the hangar for 5 days until I came back to fly again.

In the case of nitrile O-rings, a brake overheating event could damage the o-ring itself, which might then result in a extrusion. Please reseal your brake with Viton O-rings. In 10-packs from Seal Source Inc. they cost $0.94 cents each.

Also remind yourself that aircraft brakes are designed for one rejected take-off (RTO). this knowledge may encourage you to practice your speed control on final approach so you can confidently land as slowly as possible.

If you have any questions about the above remarks please feel free to post or PM me.

Larry Tompkins
544WB -6A purchased flying
W52 Battle Ground WA
 
seal source orings

Do you have the part number of the Viton orings from Seal Source.

Thanks,
Dennis
 
3. Shouldn't an A&P know which way the piston goes in?

- but I just couldn't bring myself to believe that an A&P wouldn't notice upon disassembly that the piston was reversed and that he would repeat
A

Do you know it was an A&P? Lots of shops employ non A&Ps working under "supervision", suposedly. I once watched such a person attempt to 'unscrew' a quarter turn cam lock on a cowling. Mount ruined, I couldn't get in there fast enough.
 
I got mine from o-rings, inc:

Products
------------------------------------------------------
10 x -218 V75 (1-1/4 ID X 1-1/2 OD X 1/8 W) (1) = $4.10
------------------------------------------------------
Sub-Total: $4.10
US Postal Service Priority Mail Flat Fee (We ship Priority mail only. We do not ship first class. (USA lower 48 states only)): $6.00
Total: $10.10

www.oringsusa.com

Good service.

- - - - - - - - - - - - -

I became aware of the problem with Cleveland 30-9 brakes after an aborted takeoff w/ heavy braking last fall. The plane stopped straight, maybe a little long. I taxiied back to the hanger and put the plane to bed. I came back the next day to a pool of brake fluid under the right gear. I'll attach photos of the disassembled brake. The piston was installed correctly, but it *appears* that a square profile o-ring had been used rather than round. Not sure if that contributed to the failure. Or could a round o-ring deform to a squarish profile under extreme heat / pressure?

34y5vev.jpg


2uoqv7a.jpg
 
I'm pretty sure they they get square when overheated.

Two notes for the thread.

Don't pop the piston out of the calipers with a blast of high pressure air. Air is OK, but use just barely enough pressure to budge the piston, and make sure it comes out square. If it cocks just a little at the last, it can catch an edge and peel the thin o-ring land as you see in post #18.

Cleveland engineers are perfectly aware of the temperature limitations of nitrile. The continue to spec nitrile o-rings because of two classic problems; re-certification cost, and covering every market segment. Viton doesn't seal as well at very low temperatures. Is that really a problem? I dunno. Seems like they use viton in automotive brakes in the arctic.
 
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