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Brake Fire Concerns?

tom_AZ

Well Known Member
Hasn't happened to me (yet, at least), but my understanding is that brake fires are often the result of o-rings that fail from overheating and then release brake fluid onto hot rotors. The brakes (Clevelands) on my -10 are OK, but maybe not as robust as they could be... I make an effort to go easy on the brakes, and lining life seems good. However, they got pretty hot once, after having to abort a T.O. (wildlife) just below rotation speed. Coupled with a local A/C (not an RV) that was lost to a brake fire a year or so ago, I started thinking about what else I might do to reduce risk.

I'm considering replacing the rubber o-rings with Viton due to its higher temp tolerance, as well as switching to a fluid with a higher flash point (Royco 782), and am hoping to leverage thoughts and experience of others before making that decision.
 
Hasn't happened to me (yet, at least), but my understanding is that brake fires are often the result of o-rings that fail from overheating and then release brake fluid onto hot rotors. The brakes (Clevelands) on my -10 are OK, but maybe not as robust as they could be... I make an effort to go easy on the brakes, and lining life seems good. However, they got pretty hot once, after having to abort a T.O. (wildlife) just below rotation speed. Coupled with a local A/C (not an RV) that was lost to a brake fire a year or so ago, I started thinking about what else I might do to reduce risk.

I'm considering replacing the rubber o-rings with Viton due to its higher temp tolerance, as well as switching to a fluid with a higher flash point (Royco 782), and am hoping to leverage thoughts and experience of others before making that decision.

Vitons are good. Also make sure to use MIL-H-83282, or Royco 782 instead of MIL-H-5606. The former is the fire resistant type with a higher flash point. That's about all you can do AFAIK.
 
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Experience

Having been the victim of a brake fire due to overzealous seasoning of new pads, I have learned this.

1) Wheel pants off during brake seasoning.
2) Seasoning is probably not necessary, but should be done by dragging the brakes at run up power for a short (1000ft) distance or so. Did I mention wheel pants off?
3) Viton Orings can help as their temperature range is higher.
4) High flash point brake fluid would help, but not prevent a fire.
5) The best thing to reduce the probability of a brake fire is to have thicker rotors. You can do this with the Cleveland kit or do what I did. I ordered new Grove wheel and brake kits with 0.250 rotors vice the 0.190 Cleavelands.

Don

I also learned that a 1.5 lb halon bottle is not enough for a brake fire, once you lose braking and the bearing grease is very hot, an RV will coast FOREVER, and even at 68 years old, I can run for a fire extinguisher like a jackrabbit.
 
other threads

Several threads on this topic - here is a helpful one:

http://www.vansairforce.com/community/showthread.php?t=16685

Bottom line is this: "MIL-H 5606 brake fluid is not what you want to use."

Another very valuable thing I learned from one of the brake fire threads is that the brake rotor mass plays a big part in defining the total braking power of the aircraft, and our standard rotors are basically designed for one hard braking session, due to the heat dissipation rate. Meaning, for example, if you use your brakes for an early exit off the runway after landing, plan to give your brakes time to cool fully before relying on them again. Not doing so is asking for an "undesired event", no matter what fluid or type of o-ring you use.

These threads provide more info:

http://www.vansairforce.com/community/showthread.php?t=10366

http://www.vansairforce.com/community/showthread.php?p=1396283
 
Am I wrong?

As far as I know, Dot 5 does not burn - tho it can get very hot. Am I wrong about this? If I am right, seems the nose draggers should be using this product exclusively.

http://www.clearcoproducts.com/pdf/msds/specialty/MSDS-DOT-5-Silicone-Brake-Fluid.pdf

Section 2 says Animal tests for similar Polydimethylsiloxane fluids suggest very low acute dermal toxicity. Tributylphosphate may be absorbed thru the skin.

Section 5 has no data on its flammable limits, meaning they could not measure that number.

Section 9 says it has no boiling point.

Section 10 of this document says it will not decompose or combust.

I do know this fluid should not be used in any ABS systems - it's too viscous.

Am I all wrong about this?
 
Dot 5.1

As far as I know, Dot 5 does not burn - tho it can get very hot. Am I wrong about this? If I am right, seems the nose draggers should be using this product exclusively. ...
Based on what I've read, I'm using 5.1 which not silicone but glycol ether/borate ester. I found this compatibility matrix here:

Brake-Fluid-Compatibility-Matrix.png


More info on the wiki: https://en.wikipedia.org/wiki/Brake_fluid

Needed to change the o-rings - which was easy thanks to Charlie and Michael's kits. This stuff is really cheap, works well, easily available. The only negative is that you don't want to get it on your paint. A small price to pay to greatly reduce the chances of a brake fire.

PS: whoever came up with this DOT numbering ...
 
Thanks, and follow-up questions

Thanks for the quick feedback, and links to previous threads.

I'll plan on the switch to Viton (if it gets to -50 degrees in Tucson, I have bigger issues to deal with than brakes) and to Royco 782.

Point taken about rotor mass being key as well, which leads to 2 follow-up questions:

1) Do you have a source and p/n for thicker rotors for the -10 (on first read, it looked like those mentioned in the threads were for other models, presumably with different rotors)?

2) Although it should become a moot point, what is the minimum thickness spec for the stock -10 rotors?
 
Break Fires!

.... We service many wheels and tires weekly and have seen evidence of fires
that the pilot was not even aware of. Most of what we see is not from brake fluid,
but rather excessive bearing grease being expelled from the antiquated wheel
bearings. This can be due to a couple of different conditions, like using way too
much grease when re-packing the bearings, or faulty old seal felt that lets out
grease when the brakes get well heated. These old, antiquated type of seals can
be very dangerous if not monitored, maintained, and replaced when needed. the
newer neoprene type seals work a bit better but don't hold a candle to the new
double sealed bearings that require no maintenance, and do not discharge any
grease at all. Any grease that is kicked out onto the brake rotors is detrimental
to brake performance, brake life, tire and wheel shake, and a possible fire hazard.
Anyone interested in eliminating these potential issues can obtain more information
on our bearing mods at our website, or just give us a call with any questions
or concerns. Be safe out there in these trying times. Thanks, Allan..:D
 
Hasn't happened to me (yet, at least), but my understanding is that brake fires are often the result of o-rings that fail from overheating and then release brake fluid onto hot rotors. The brakes (Clevelands) on my -10 are OK, but maybe not as robust as they could be... I make an effort to go easy on the brakes, and lining life seems good. However, they got pretty hot once, after having to abort a T.O. (wildlife) just below rotation speed. Coupled with a local A/C (not an RV) that was lost to a brake fire a year or so ago, I started thinking about what else I might do to reduce risk.

I'm considering replacing the rubber o-rings with Viton due to its higher temp tolerance, as well as switching to a fluid with a higher flash point (Royco 782), and am hoping to leverage thoughts and experience of others before making that decision.

I am making this exact conversion on the -6 right now. In fact, the plane is up on blocks because the new brake pads I purchased don't fit, so I had to order a different set.

I've seen one gently flown -10 with smoking brakes and another one at Oshkosh that blew a caliper seal. -10's with the standard brakes are closer to the margin than I want to be. To help, I went with Matco brakes on the -10 for more braking capacity and plan to use the Royco fluid.
 
Rotors

Grove Aircraft can sell you the rotors - but remember that you will need a shim for the caliper when installing the thicker rotors.

https://groveaircraft.com/wbproducts.html

The F1 uses the 56-1 kit, which has a 0.313" thick rotor. Plenty of braking power for 2000lb gross weight out of those parts.

I think the rotors would swap with the Cleveland parts....but be sure to get the shims!
 
Perhaps Allan could come up with a brake caliper modification service to end this silly problem once and for all.

Take Porsche brake calipers for example. Porsches are well-known for for having brakes that hold up well under extreme temperatures.

In a nutshell, implement an outer seal, use a hard-anodized piston thats less susceptable to scratching, and a square cross section nitrile oring. In our case the oring would move from the piston to the caliper.

Almost every GA airplane I work on leak fluid at the caliper.

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pic03.jpg
 
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