Brake Fluid

[Rotary10-RV]

Well here goes,
I have seen it posted that some aircraft brakes are not compatible with automotive brake fluid. One manufacturer said the seals weren't compatible. (Matco I believe) Then they list the material as Buna-N which is used on most auto brakes! Cleveland says auto is OK. I have used all sorts of brake fluids for racing and street use and never had a problem. Can anybody really tell me WHY there is a aviation brake fluid. (other than to make somebody money!)
Bill Jepson
RotaryRV-10

[Mel]

Auto brake fluid is vegetable based & Works with rubber seals. Aircraft brake fluid is petroleum based & Works with neoprene seals. The 2 are not compatable.
Mel...DAR

[jonbakerok]

Since I moved down here to Houston, several people have told me that I need to flush my brake fluid ever couple of years because it supposedly absorbs the extreme Houston humidity and turns to mush.

And get this -- a number of them told me that they had long ago switched to auto brake fluid (in their certified planes, no less), to avoid the regular flushes. I'm pretty sure they said they were using "DOT 5". This really amazed me, because I once ruined the brakes on a Harley years ago by adding DOT 5 to a DOT 3 system, which turned the fluid into rubber. I think the main difference is that DOT 5 is synthetic and DOT 3 is mineral oil (like aircraft brake fluid).

I'm sticking with Aircraft fluid, but I wonder what the truth is.

[fehdxl]

Merely another data point... my recollection is that Type-F automatic transmission fluid is very similar to MIL-H-5606G, but likely a lot less expensive.

YMMV.

-Jim

P.S. Off topic, but my 1982 Harley uses DOT 5 brake fluid. Main advantage IMO...it doesn't destroy the paint when (not if) it comes in contact with the tank/fenders.

[Tandem46]

I was forwarded this by a friend. This is scary and just happend recently.

Tobin

For those interested (and may not have seen them) , here are a few photos of my brake line fire incident.

Big chunk got blown out of brake line as can be seen from Brakelines.jpg photo. Effect of resin burning seen on wheel pant photos. Once the line broke, the next time I depressed the brake pedal, a fireball from the wheel to over the wing resulted from spraying the hydraulic fluid over the hot brake assembly. The flash point of the fluid is only 240F! I am going to investigate some stuff with a bit higher flash point {:>)


Ed

[gvgoff99]

Ed, WOW, What a mess. Sorry that happened. One thing that I think I am seeing is that you used a dry chemical fire extinguisher to put out the excitement. You might want to look on eBay for a Halon extinguisher. The Dry Chemical puts out the immediate problem but creates a never ending problem. It is like dunking your airplane in salt water. The stuff gets into everything and is virtually impossible to remove. It will corrode whatever metal it touches.
You are probably OK (if that is what you used) since it looks like it was directed at the wheel. You can probably clean the stuff off because it is so localized. If it had been in the cabin or engine compartment it would be the slow kiss of death.

[Tandem46]

Rotary10-RV says that Cleveland says its ok to use auto brake fluid, so why can't we? I know someone (don't want to throw names around here) that has been using DOT 5 (silicon based) for two years on his RV-6 with no problems. Is there some other non-compatible part like the hoses that won't allow the use of DOT fluid? If not, I'm switching. I don't like having that flammable stuff up under the dash with that plastic tubing coming from the resevoir, let alone down by the hot brakes.

Tobin

[Rick6a]

Interestingly, I received transition training from Ben Johnson (one of the few RV transition pilots endorsed by Van's and Nationair) in the Dallas area several weeks ago in his RV-6A. When I asked..."Why no wheel pants?" He responded that he was doing some high speed taxi tests and the brakes caught on fire! Trashed one of the wheel pants that's for sure. Luckily, a nearby witness put out the flames with an extinguisher. It was that event that motivated Ben to invest in a small halon fire extinguisher and he strongly urged me to keep one stowed in the cockpit. I do recall he mentioned that Van's was well aware of the brake fire problem. Lesson....don't lean on the brakes too much. I'd be interested to know just HOW much of a problem this really is.

Rick Galati RV-6A "Darla" 36 hours

[gmcjetpilot]

I would never use plastic or aluminum break lines near the caliper. I used a #2 hose like this.
http://www.raceplumbing.com/product_...roducts_id=213
http://www.bonacoinc.com/teflon_brake_lines.htm

I ran the small braided line all the way from the caliper to the firewall. You could run a shorter piece of braided hose from the caliper, than transition half way up the gear leg to aluminum, but less joints and connections are better. The temp rating, flexibility and durability of the braided line is much better than plastic or plan aluminum tubing. When plastic was used many failed, but you don't hear about them and lucky even fewer caught fire.

The down side if any of the braided hose is a little more weight and cost. I had mine made up at an industrial hose house that had the proper 37deg fittings. The cost for the two lines was not much. Also before the fittings where installed I slipped a short piece of clear vinyl over the braided line. This was to avoid any abrasion of the hose braid rubbing the wheel pants or bottom of the gear leg fairing. Going for 1000 hours and 7 years and no problem. Also for maintenance when you move your caliper, the flex line allows the caliper to set it a side without disconnecting it.

Also people who know more about the subject state the Mobile 1 synthetic ATF works well and has double the flash point temp. The down side is there are other additives that are not really needed for a brake system, however those who use it say the extra additives have no negative affect on the brakes. Those who use it say it has worked for them for years. Apparently the additives like anti-friction or detergent compounds only work at high temps.

There are better Mil spec brake fluids, like MIL-H 83282, but only come in 4 gal quantities as I am told. It has twice the flash point of the older MIL-H5606 fluid, and some think it is just like synthetic ATF fluid. It would be nice if Van or someone who sells parts would buy MIL-H 83282 to sell in small amounts to builders. We can always make our RV's better and safer. No need to use 65 year old MIL-H5606 brake fluid formulas when MIL-H 83282 is available (kind of). I don't know if the two MIL specs are compatible.

Last DON'T ride the BRAKES! The best way to do it is check speed to a crawl than let them go *completely* (feet off) and let the speed build up, than check speed again, repeat as necessary. Just dragging the brakes continuously will give you a brake fire real fast. The process of brake / release allows some brake cooling. It is all energy and it has to go somewhere. Remember, also those cool looking low drag wheel fairings are not letting the brakes get much cool air.

Cheers George

(NOTE: I am not implying that this brake fire was avoidable or the fault of the pilot. It was constructed per plans as many RV's have this set-up. Also I am not implying he was riding the brakes. However I do know that many brake fires have been caused by riding brakes on all kind of aircraft, including small GA planes to larger commercial aircraft. If you have a long taxi keep that in mind.)

[szicree]

George,

I sure like the idea of stainless all the way, but I know nothing about the stuff. I think I'd like to have a line from my master cyl. to a bulkhead fitting on the side skin adjacent ot the firewall, and then another line all the way to the caliper. You said you used #2, but I think #3 is closer to the plastic stuff called out in the plans. As for making the lines, what's involved? Is this something we can do ourselves or do you need some super expensive tool? Thanks in advance for the assist.

Steve Zicree
RV4 finishing