Viton O-rings in Clevelands?

[Radioflyer]

I'm considering replacing the standard Buna-N O-rings in my brake calipers with Viton. Canard brakes get very hot and Viton is superior in heat tolerance. Is anybody already using Viton O-rings with their Clevelands (30-9)?

[Joe Person]

I'd check with the Cleveland brake people first, before making such a switch, just to be safe.

[flyingwaldo]

I'm using what I believe to be Viton O-rings from and in my Groves.  I recently overheated my brakes.  When I pulled the calipers to check the O-rings they were all shot.  A ripped looking groove had appeared along the edges of the rings. 
I'm using DOT 5 fluid so I don't think the fluid would have caused this since my research says it is fairly benign on most soft components, but I may have come to the wrong conclusion.  I think the Viton products are better able to work with different fluids? 
What caused the overheating was a stupid mistake (over taxi testing new nose gear components without removing wheel pants) which I'm hoping not to make again so this should be the last replacement of the O-rings for some time.......
Am looking forward to more opinions.

[Radioflyer]

I personally have not checked with Cleveland, but have read about others who have. Cleveland seems to say that they would be all right, if not superior, except in extremely cold weather. Typical New England weather would be OK, but perhaps very cold Canada would not be an ideal climate. Apparently, only reason Cleveland does not outright recommend them is simply because they don't want to go thru the certification hastles.
There has been much talk and justification for using Viton in brakes, especially in the RV crowd, but I cannot seem to locate someone who actually has used them. I will try them, bit I'ld feel better hearing from someone who has already tried them.
Waldo-I would be surprised that if the brakes got hot enough to harm Viton O-rings that you did not also melt/deform your gear legs. It would be interesting to see if Grove does use Viton. Tolerance to these high heat situations is what using Viton O-rings all about.

[flyeyes]

I have used them in the Cleveland brakes in my RV-8 successfully for a few years.  I have also given several sets to friends (I ordered a couple of dozen to make a minimum order).

Fair Warning--I am not an A&P, and engineer, or any type of expert in airplane brakes.  Do your own research, yadda. yadda...

I also switched to MIL-H-83282 brake fluid in place of the more common 5606.  This is a chemically compatible (with the 5606) fluid that can be added to systems that have had 5606 in them previously.  It does have a significantly higher flash point than the 5606 and is commonly used in larger turboprop/commuter aircraft.  You can mix the two fluids if necessary.  5606 is only used in small GA aircraft for legacy reasons as far as I can tell.

Google MIL-H-83282 and you will find a lot of info.

It is my (inexpert) opinion that switching to Viton O-rings and 83282 is cheap, easy, harmless, and reduces the risk of a brake fire.  I think this is especially important in aircraft like EZs or -A model RVs that are dependent on brakes for steering.

The failure mode seems to be that the O-rings overheat, and become relatively square in cross section.  Then, on the next brake application, brake fluid gets past the seal and on the hot brake disc.  With 5606, the flash point is only 250 degrees or so.  I think the disc gets a little hotter than that.....

[Radioflyer]

Excellent data point, thank you flyeyes! I already have my Aeroshell Fluid #31 (83282 brake fluid). Even Cleveland recommends 83282, it is a no brainer. Since it is not readily available, I ordered a gallon can to split with a friend from the oil-store.com for $40, shipped.
I'm definately rebuilding my Clevelands with the Viton O-rings. McMaster Carr has the AS568-218 Viton O-rings which are the exact physical dimensions as the Cleveland Buna-N MS28775-218. McMaster's catalog number is 5267T183, $14.03 per Pack of 25.

PS-Was the failure mode described, squared and leaking, referring to the Buna-N O-rings, I hope?

[Tom]

Hi folks,

My 0.02

Viton orings as do HSN or HNBR orings come in differing compound or "recipes",
Saying an oring is "viton" is similar to saying it is "rubber"  most companies dont go into this
detail, but is worth noting.

Typicaly the best all around orings that we use (in the oil and gas world) are HSN 80 durometer (or the hardness)

"viton" usually comes in 90 duro, so they are a bit harder, and thus more prone to leaking at low pressure, for my money and time
the next time I rebuild my brakes on  the eze, Im going to open up the width of the oring groove to install a split back up ring, most likely
peek or teflon, this will GREATLY increase the reliability of the HSN 80 orings at high temp.

as for sizes, a 218 oring is a 218, regardless of material.

from what we have seen, MMC orings are kinda crappy chinese products.  its best to buy seals from reputable seal companies that
keep their inventory fresh, and traceable.

also, from what I have seen, you are much more likely to have a brake fire by rupturing the nylaflow lines, than failing the oring. it should be a mandatory change to install a short "pig tail" of steel or alum tubing right at the caliper for a short bit

T

[flyeyes]

The failure mode was referring to the original Buna-N rings which came in the brakes.

A CFI friend of mine had a brake failure in the right brake of his RV-8A which caused him to leave a taxiway, fortunately with negligible damage.  He is very cautious about his brakes, but had recently given a checkout in the airplane. He has since upgraded to Viton/83282.

There have been a significant number of brake failures (almost always the right brake, because of engine torque) and a small handful of brake fires in nosewheel RVs.  I also follow the Cirrus lists, and there have been a handful of airframes lost to brake fires on the ground.  There was an AD in the Cirri requiring larger brakes, vent holes in the wheel pants, and "telltale" stickers on the brakes which change colors if they overheat.

The tailwheel RVs are less susceptible, because they have steerable tailwheels, and the TW configuration discourages heavy brake use anyway :-)  There was one RV-8 incident resulting from forcing the airplane onto the runway at high speed and braking heavily (very tired pilot making a round-the world flight being yelled at by foreign controllers at the end of a multi-hour overwater leg).

When I bought my O-rings, they were available in 75 and 90 durometer.  I bought a selection and have installed only the 75s so far.

[Radioflyer]

The McMaster O-ring catalog number I mentioned is for the 75 durometer Viton. The Cleveland specified Buna-N O-rings are 70, so I figured I better stay as close as I could to that softness. I would have to disagree that saying Viton is like saying "rubber". However, I do know there are several Viton formulations, but the standard "A" formulation seems to me like the best for this application. Ordering from McMaster's is easy for me, but if there is a better brand or vendor, it would be good to know.

Incidentally, I just looked at some specs for the HSN/HNBR formulation. Seems much superior to generic Buna-N, but there was specific warning against using with brake fluid. The reference didn't mention which kind of brake fluid. I'm not expert at any of this, but I have not yet come across any such warning against Viton.

The point about keeping the Nylaflow a bit further away from the calipers makes sense, even when using the 83282 fluid. I'll look into how I can do that with my LGEZ.

[Tom]

"brake fluid" as described by oring companies, refers to DOT 3/4 etc...

The aeroshell hydraulic fluid is NOT brake fluid.
if you are at all concerned, simply put the orings you want to use
into a jar with the chemical or fluid that you will be using. leave it for a couple days
and then inspect it to see for signs of chemical attack, the oring will either swell
or become brittle. Actually this is good practice to do anytime orings are replaced with
new units of questionable quality.

There is an SPE paper that a co-worker of mine wrote on oring selection, I'll see if I can dig it up and post it

try sealsonline.com,