Brake fluid?

rvator9a · #1 10-29-2007, 11:42 AM

What is the proper brake fluid to use in an RV, And where is the best place to obtain it. Does anyone bleed brakes the way they are commonly bled on a car or is it advisable to pump the fluid into the calipers from the bottom?

f1rocket · #2 10-29-2007, 12:05 PM

There are several threads in the archives where this is discussed. I use Mobil 1 synthetic ATF fluid as brake fluid. Much less caustic, not flamable, and available at any parts store.

I bleed from the top down with a closed system.

John Clark · #3 10-29-2007, 12:09 PM

This is yet another topic that has flogged before. You might want to search "brake fluid" and read the posts. The bottom line is some prefer aircraft fluid (mil 5606) becuse it is compatable with the seals provided and in not hydroscopic (wil not mix with water,) The other side of the discussion is automotive fluid which is "fire proof" but will absorb water. Automotive fluid is good for higher temperatures and is an excellent paint remover.

In my experience, bleeding most RV systems is best accomplished by pumping fluid from the calipers up. Conventional bleeding will not clear the air from some of the "loops" of tubing in the system.

John Clark
RV8 N18U "Sunshine"
KSBA

randylervold · #4 10-29-2007, 07:29 PM

"Standard" brake fluid for GA aircraft is MIL-H-5606. This fluid has been around forever and works fine, but can be improved upon. MIL-H-83282 was introduced a few years back and is a semi-synthetic upgrade. It performs better in every regard, but of special interest is the flash point. 5606 has a flash point of around 225? whereas 83282 is around 425?. This can be a factor with RVs because there have been several reported cases of brake fires on RVs and some have taken the whole aircraft with it. Do yourself a favor, upgrade the standard MIL-H-5606 to MIL-H-83282: Royco 782 or Aero Shell 31

rocketbob · #5 10-29-2007, 07:55 PM

Mobil 1 synthetic ATF specs are almost identical to Aeroshell Fluid 31 (I've checked). Available at Walmart.

Best way to bleed is to connect a tube to the reservoir which goes into a container of fluid to capture overflow and use a pressure can to bleed the system with a significant volume of fluid, from the bottom up. I made a pressure can with a valve and some fittings on an old solvent can. It connects to shop air, turn the valve on and go. Just used this setup on a J3 last weekend on which I swapped the expander brakes with Grove disc brakes. It took me about 30 seconds to bleed each side. Completely foolproof.

Caveman · #6 10-29-2007, 10:19 PM

What does converting my RV to Mobil 1 synthetic ATF entail? Different o-rings? What kind?

Mel · #7 10-30-2007, 08:06 AM

No changes necessary. The fluids are compatible.

FredMagare · #8 10-30-2007, 11:59 AM

Quote:

Originally Posted by rocketbob

Mobil 1 synthetic ATF specs are almost identical to Aeroshell Fluid 31 (I've checked). Available at Walmart.

Best way to bleed is to connect a tube to the reservoir which goes into a container of fluid to capture overflow and use a pressure can to bleed the system with a significant volume of fluid, from the bottom up. I made a pressure can with a valve and some fittings on an old solvent can. It connects to shop air, turn the valve on and go. Just used this setup on a J3 last weekend on which I swapped the expander brakes with Grove disc brakes. It took me about 30 seconds to bleed each side. Completely foolproof.

I seem to remember someone writing about how they used an ordinary plastic garden sprayer (for fertilizers/weed killers, available at any home improvement store) as a pressure vessel by attaching an appropriate hose to the end. Fill it with fluid, connect it to the nipple, pump it up, and squeeze the trigger. What a GREAT idea!

rv620mr · #9 10-30-2007, 05:04 PM

I'd like to use Mobil 1 Synthetic ATF as brake fluid. I just pulled the technical specs on both mil spec 83282 and Mobil 1 Synthetic ATF. I used ExxonMobil's website. Mobil's trade name for 83282 is Mobil Aero Grade(1) HFS.

I'm no engineer. I'm listing these particular specs just because I was able to find these particular specs for BOTH fluids.

Viscosity at 40 deg C is 14.2 cST for the 83282 equivalent. Viscosity at 40 deg C is 34 cST for the ATF. At -40 deg C it's 2000 vs 5190. I don't know if that's significant or not.

Flash points are quite similar at 224 deg C vs 236 deg C. Pour points are quite similar at -60 deg C vs -54 deg C.

The ASTM D 2270 viscosity index seems acceptable at 128 vs 199. For reference, mil spec 5606 has an index of 370.

The specific gravity/density (ASTM D 4052) seems similar at 0.851 vs 0.837. For reference, mil spec 5606 is 0.881. There may be some temperature differences here in the testing at 60 deg F/ 60 deg F vs 15 dec C kg/l.

What risks are involved in using Mobil 1 Synth ATF in RV brake systems?

f1rocket · #10 10-31-2007, 12:03 PM

Uh...I think you answered your own question!