Open Brake Fluid Can-Problem? Need Advice

[911pcars]

"ATE 1/2 the price of the RBF from my source. Well, it's the same price for 1/2 the quantity, and I tend to flush a whole can of ATE just for good measure... maybe I need to be more efficient. That said, I'm planning to try the motul RBF 600 next."

Andy,
You're probably right with the pricing. However, the ten buck difference can be made up by potentially not having to bleed brakes after a session or by stopping a few feet further from a wall or other immoveable object (that was for effect). :-)

Motul RBF is about $10 for 1/2 liter in my area.
ATE is about $12 for one liter (PParts server was slow so couldn't verify)

Sherwood

[KobaltBlau]

Point taken, Sherwood.

Randy, how bout them curves? (see my previous post)

If I knew roughly how long it takes to get from the dry boiling point to the wet boiling point I could potentially save a lot of changes, and also evaluate whether SRF is a good buy for me.

[KFC911]

Originally posted by KobaltBlau
...and I tend to flush a whole can of ATE just for good measure... maybe I need to be more efficient....

Although flushing with ATE won't 'break the bank', I keep a large container of the 'cheap stuff' handy for flushing (doesn't matter if it's been opened a while). This also helps when replacing ATE blue (with blue) since I've got a color change in between.

[randywebb]

"can you point me to these curves?"

Check the sites for fluid manfs. Some have been in articles in Pano. They are declining hyperbolics from dry to wet b.p.s (think about the rate process and it will make sense). Yes, they are based on ambient absolute humidity and surface area of fluid exposed to the atmosphere. The latter is low in your brake system.

The easy answer was posted above - use Motul.

A couple years ago I posted a compilation of wet & dry b.p.s for various fluids.... As I recall, there is a Ford fluid that is good for the price if you are a cheapskate....

[KobaltBlau]

Randy, what does b.p.s. stand for? I looked on the ATE and Motul sites but didn't have luck, as well as the hype-y GS610 site.

I also searched for a post of yours using "ford" "brake fluid curves" "b.p.s." and a few other things but no luck.

I'll see what I can come up with on the pano angle. I really would like to understand what the curves look like.

[randywebb]

Andy -
b.p.s = boiling points

- For shape of the curve, start up high on the Y-axis at the left, and ride a roller coaster type curve down to low on the Y-axis at the right hand side....

I don't know if Pelican has brake fluid or not - I imagine they do.

some tidbits:

wet b.p.
318 Castrol LMA
421 Motul Racing 600
392 ATE Typ 200 / Supre Blue (metal can)

dry b.p.
446 Castrol LMA
585 Motul Racing 600
536 ATE Typ 200 / Super Blue


my original post from Rennlist text list maybe -- June 2001:

Type 4-200 drops from a boiling point of 545 oF when dry (0% moisture absorbed) to 392 oF when "wet" (~ 3.4% moisture absorbed). Porsche says you can go 3
years before changing with this new fluid. It is based on a mixture of glycol ethers and borate esters rather than silicones. It was developed in conjunction with Ate, and Ate Super Blue Racing seems to be identical. DOT 5.1 brake fluids (such as Motul 600) do even better -- these are also
synthetics but not silicones. The Motul 600 is reputed to be as expensive as liquid gold, and is hard to find in some areas.

If you go to various dealers and ask what is their best brake fluid for high performance cars, yout get the following b.p.s in oF:
DRY WET
536 392 Ate Super Blue Racing
510 360 MB DOT 4 Plus
446 311 BMW DOT 4
>500 329 VW-Audi DOT 4

The BMW seems to be the same as Castrol GT LMA (low moisture absorbtion). I looked at 2 cans of MB fluid (lare and small) -- they varied slightly in wet and dry b.p.s. It's not clear what "DOT 4 Plus" means but it doesn't match
the Ate Super Blue. I would go with the Ate over the others.

The unknown in all this, is how much moisture a given fluid will absorb from the air. That was the LMA in the Castrol fluid (which used to be the hot ticket a while back). It's possible that putting the Ate/Porsche DOT 4-200 fluid in the same moist air as, say, the MB fluid, that after a year or so the MB fluid would have less water in it and perfom better.

References:

Panorama Oct. 1998, p. 65-74

http://www.shotimes.com/SHO3brakefluid.html
http://members.rennlist.com/911pcars/brakefluid.htm

UpFixin' vol. 7, p. 162 -- an older Bruce Anderson article on brake fluid


- If you can't tell, I I've just changed my brake fluid....

- Randy

"The mathematician, Georg Cantor, went insane from thinking about the real line."

[KobaltBlau]

Thank you Randy for your very detailed and helpful response. The important info for me is based more than anything on the information on that SHO page (hope it's right).

In particular, "SAE field tests have shown that the average one year old car has 2% moisture in the fluid" and your statement ""wet" (~ 3.4% moisture absorbed)"

And though the curves are steep, a 1% moisture absorbtion isn't going to make a huge difference, and it isn't going to happen really fast if you have flushed your system several times in the last 5 years, especially in dry Denver

I often get a bit of soft pedal toward the end of a DE run session. This is with a full weight SC with stock SC brakes, 993 diverters and smart racing block-off plates, and track specific pads. I know a real brake cooling kit would be better but I don't want to be tearing through expensive hose. Anyway, it's on my list.

So if I get a little soft pedal I am getting some localized boiling, most likely on the back side of the caliper pistons. Does this decrease the performance of the fluid for the next event a week or two later?

Thanks,

[randywebb]

Good question - My bet is you will get 65 opinions but the only real answers will be in SAE papers etc. Bill V. might know...

You could do some stopping tests after it happens and see what you think.

Also, there are labs that will test brake fluid...

[911pcars]

Anytime the fluid boils, air forms in the system. Air is compressible which takes up pedal travel and leaves you with less to squeeze the rotors. Given only X amount of travel by the factory, you don't want to test the flexibility of the floor board.

To help retard heat transfer to the brake fluid, caliper manufacturers sometimes use ti or stainless steel to shield the inside of the caliper (facing the rotor) or even use caliper pistons made of ti.

These are Ti Brake Shields. They fit between each brake pad and the caliper piston. They work on the same principle. Ti is light and has low thermal conductivity. In borderline cases they help prevent fluid boiling, especially if class rules limit the brakes you can use (e.g. VARA, POC, etc.). I usually recommend them after an owner has installed ducting and good brake fluid. The next step beyond this is a big jump: larger calipers and rotors. It would be nice (and expensive) to have brake pad backing plates made of this material.



Sherwood
www.seinesystems.com

[cgarr]

Why cant you just boil out any moisture (heat up your fluid to 212) before you use it?

Craig

[randywebb]

I dunno.

A couple of ideas on why:
- troublesome and fluid is cheap
- water may bind chemically
- water may alter the chemical composition of the fluid (note how ugly it looks when old)

[tshih]

Randy,

Sorry to disagree with your last few guesses.
Heating up the fluid is good for purifying it. That's how it was dried in the first place by vacuum distillation. The troublesome and costs effectiveness part I agree totally. Fluid is cheap especially Valvoline Synthetic $6/liter at Pepboys I believe same bps as ATE.

The water doesn't chemically bind to the BF. It's just dissolved completely. One can dry the water out of the BF by adding 4 angstrom molecular sieves (available from Chemical Specialty Firm Sigma-Aldrich via website www.sigmaaldrich.com) and filtering to remove particulates (which can plug the lines-much worse scenario than wet brake fluid!!).

Water doesn't alter the chemical composition of the BF except make it wet. The coloration is from corrosion of the steel lines and internal caliper parts due to water being present. The black color of really old fluid is from rubber decomposition of the internal lines and parts around the MC seals.

Finally the BF in the can opened once but sealed tightly is much drier than the BF in the car because the brake fluid reservoir in the cars are vented to the outside air and picks up moisture over time. There is an overfill drain that vents the reservoir to the outside via a hose (about 5 mm diameter) and permits the reservoir to dispense fluid into the hydraulic lines during braking without forming a vacuum (as in the case when such a vent is not there).

Also for those with access to industrial labs there is a device which potentiometrically titrates for amount of water in organic liquids (like BF based on ethylene glycol trimers or quadramers).

The reason why water leads to soft brake pedal is its boiling point (temperature it turns from liquid to gas) is 100 deg C or 212 F and the brake fluid temp easily rises above that (300-400 deg C). Hydraulics work based on the incompressibility of liquids not that of gases (steam).

[autobonrun]

Tshih, don't mole sieves have to be regenerated using heat and reverse flow to remove the moisture they absorb? Wouldn't it be easier to just flush and replace the fluid regularly rather than trying to have a closed loop brake fluid system? I agree with the filter. It would be required to catch particulates that get released from the mole sieve.

Also, the boiling point you mention of 212 degF is at atmosphere. I would assume the fluid downstream of the master cylinder is under pressure so the boiling point would be higher. Not as high as brake fluid obviously but higher than 212 degF. Anyone know what pressure the master cylinder generates in the system?

[911pcars]

Interesting discussion. I'll let the physics and math guys compute the active brake pressures (several hundred psi), but when at rest (brake pedal up), the brake system pressure is the same as atmospheric (14.7 psi at sea level or zero gauge pressure), thus any moisture in the unpressurized system hot enough to boil will do just that (typically the fluid in the caliper and specifically next to the caliper pistons). After the moisture changes state from liquid to vapor, it stays in that state. The next time the system is pressurized, the air bubbles compress and displaces the movement of fluid it would normally take to move the pistons.

Sherwood

[Craig 930 RS]

An idea:

Vent the reservoir to a small container of dessicant. Dry air !

[911pcars]

"Vent the reservoir to a small container of dessicant. Dry air !"

Okay. That would work, but what about the humid air on the other side of the dessicant? The reservoir must always be vented to atmosphere to prevent a vacuum.

I'm sure a closed system could be devised to supply dry air to the brake system. Sounds like a worthy invention, but perhaps using brake fluid with a higher wet rating accomplishes the same effect.

Sherwood

[randywebb]

no need to be sorry - that's why I posted them as "ideas"

Autobon - Note he agreed with the effort req'd -- so you two (or all of us) are saying the same thing -- it's just a point of interest (unless you plan to start a brake fluid recycling plant...)

dessicant would work but then there'd be the hassle of frequent changes or reheating to drive off its mositure...

I recall seeing some figures on prssures in the lines once but don't recall them. I expect the title of the thread will attract Bill Brakeburg, who probably knows that ...

[autobonrun]

[QUOTE]Originally posted by randywebb
[B]no need to be sorry - that's why I posted them as "ideas"

Autobon - Note he agreed with the effort req'd -- so you two (or all of us) are saying the same thing -- it's just a point of interest (unless you plan to start a brake fluid recycling plant...)

No fluid recycling plant for me, just an interesting discussion as you said.
Sherwood, you're correct, I was thinking about the boiling point under braking rather than at rest. Ok, here's the solution. Keep the fluid volume immediately near the calipers under enough pressure to keep the boiling temperature up. That will raise the boiling point where vapor never forms. Use a small metal piston (like that in a shock absorber) to isolate the two fluid systems. Then design the MC so that it applies enough pressure to overcome this set pressure in the system. 2000 psi hydraulic hoses should work. Then you only need to make the system smart enough to vent off the set pressure if a MC failure is detected so the brakes can have a manual fall back position. No more fading brakes and no need to ever change the fluid. Ok, who's writing the patent.

[Craig 930 RS]

Motul is a better fluid than ATE Blue higher wet & dry boiling points.
It doesn't stain everything blue -
It is effectively 2X the price, but think about this........how much is your car worth/HOW much did you pay for it?

Don't get thrifty with fluid changes.

[911pcars]

" Keep the fluid volume immediately near the calipers under enough pressure to keep the boiling temperature up. That will raise the boiling point where vapor never forms. Use a small metal piston (like that in a shock absorber) to isolate the two fluid systems. Then design the MC so that it applies enough pressure to overcome this set pressure in the system."

Good to see the thinking cap ON. However, I believe it takes about 3 lbs of pressure to increase the boiling point of water 1 degree F. It seems that to increase the boiling point a significant amount, the increased pressure in your proposed system may extend the pistons and create brake drag.

It's probably a cost versus effective issue that prevents another system from being adopted. High temp brake fluids and brake fluid recirculating systems are available as are many other brake cooling schemes.

Sherwood