Comments on brake fluids

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Consider the whole point of brake fluid: to transmit mechanical energy through a hydraulic system. To do this task, the fluid has to be one major thing: not compressible. We add a whole bunch of other things in there like corrosion inhibitors (rust is A Bad Thing for your hydraulic system), lubricants, and I-don't-know-what-else. But, if the hydraulic fluid can remain incompressible, it will do its job well.
So why the need for a "high performance" brake fluid? When you boil brake fluid, it evaporates into a gas. Uh-oh, gas is compressible. If your fluid boils then the efficiency of transmitting the mechanical energy of your brake pedal into the caliper pistons is compromised and you get a dead pedal (which is only ONE of the reasons for a soft pedal, BTW. Don't jump to conclusions.) The solution for boiling brake fluid is to use one that has a higher boiling point, one that will withstand the heat better.
Brake fluid has two boiling point measurements: a dry boiling point and a wet boiling point. The difference? Brake fluid is hygroscopic, it absorbs moisture. As it absorbs moisture, its boiling point goes down. The DOT labels that you see on cans are ALWAYS the WET boiling point. The DOT did this because a lot of folks would flush their brakes once in the lifetime of their car (or when they blew a slave cylinder), so the brake fluid had years to pick up a lot of moisture from the air. Thus, for them, the important number is the wet one, because that's the level of protection that folks could expect in their Dodge Dart 10 years down the line; the brake fluid would never boil below that wet number.
Moisture can be introduced as liquid water (you put water in your master cylinder reservoir, tut, tut) or it can be from the humidity in the air. There's some measure of moisture in the air all the time (unless you're in Death Valley) so the longer your brake fluid is in your car, the more moisture will get into your braking hydraulics. This is also why you do not want to leave a can of brake fluid sitting when you use some of it (open it, use it all within about 30 days or so, then discard it.)
Well, we as hot-rodders (uh, 'scuse me, "tuners") are pretty good about replacing our brake fluid on a regular basis. If you get your fluid flushed out annually, say, and your master cylinder reservoir cap is in good shape (no leaks) then we don't need no steenkin' wet boiling point! All we need to know is at what temperature the fluid will boil DRY. And that info is readily available on the label, if not from the MSDS.
This is why some high-falutin' expensive brake fluids are still DOT 3 rated. Their WET boiling point is within the DOT 3 standards, while the DRY (new) boiling point is pretty up there. This also explains why a DOT 4 or 5 standard fluid is not necessarily "better" than a good ole DOT 3 fluid for our uses; the DOT 3 fluid may have a low wet boiling point, but its DRY boiling point is very high.
Go out there and compare the DRY boiling points of all the fluids you're looking at, and you'll be quite surprised to find that Ford factory truck brake fluid, a DOT 3 fluid, has a dry boiling point of WAY up there with the rest of them (can you imagine the heat generated by a braking semi?), at about $3 per pint. Trucks get serviced regularly (we hope) so these guys aren't too interested in the wet point, only the dry. I dare ya, grab your expensive brake fluid and compare them...
Finally, on a bit of a tangent, do you really NEED a higher-temperature brake fluid, one that adds 50 degrees to the dry boiling point for a lot more coin? How do you KNOW that you're boiling your brake fluid? The only way you can know that for sure is to measure the temperature of your fluid. Unfortunately, unless you've got a way to stick a thermocouple inside your calipers chambers you have to measure it inferentially by the temperature of the caliper body. There are cheap stick-on devices you can use to measure the temperature of the body of your calipers, and you can see if you're even coming close to boiling the fluid. I'm betting you're not.
The only way you can boil your brake fluid is to get the calipers very hot (duh!) It's not likely that you can introduce enough heat into the brake lines, or generate enough heat with the mechanical flow and compression of the fluid, to get it very hot on its own. Thus, the way heat is introduced into the caliper body is by being transferred from the friction surfaces. This means heat has to come from the rotor/pad interface, through the pad material, through the pad backing plate, into the piston and then into the fluid. In our street cars, even during "driver education" events, it is highly unlikely that we can heat up the brake fluid to the point of boiling, unless the remainder of our brake system is VERY good (possible) and we're not cooling the brakes between corners (unlikely).
However, on our street cars it's much more likely for us to fade pads and/or rotors and suspect that it's the fluid. When you fade the pads/rotors what you feel is that the harder you push on your brake the less "whoa" you're getting, but you still feel hydraulic pressure. You feel like you just can't get the car to slow down the harder you push and pumping the brakes has no significant effect (unless, of course, it allows the brake to cool a bit between pumps). This is NOT boiling fluid, this is fading the pads or rotors.
When the brake fluid boils, you'll know it, brother; your pedal is likely going to the firewall and your undies are getting soiled. In this case, pumping the brakes will bring the pedal off its stop and give you some hydraulic pressure, because you're adding additional hydraulic fluid from the reservoir to compensate for the compressed boiling fluid. Want to see what it feels like in the safety of your own garage? Next time you're bleeding the brakes, press down on the brake pedal and have a buddy open a bleeder valve. Feel the pressure go away and feel the THUNK when the pedal hits the stop. THAT'S what boiling fluid feels like, not the spongey feeling you get with faded pads/rotors.
If you're spending a lot of money on brake fluid without instrumenting the temperature of the fluid, you're using junk science, innuendo, and poor conclusions. Go to Racer Wholesale (http://www.racerwholesale.com) or someplace similar and buy some of those caliper temperature testers, stick them on your calipers, and know for sure.
Even better, they also sell a temperature paint that you dab on the edge of the rotors. It changes colors permanently when exposed to various level of high temperature. You compare that changed color to the label on the side of the bottle (like a PH test) to determine the highest temperature that your rotors experienced. Of course we all know that you're working with the pad manufacturer to find out the optimal temperature range for the pads you've chosen, as well as with the rotor manufacturer to determine the ultimate limit of their rotor's metallurgy. So now you know that you're staying within the temperature limits of fluid, rotor metallurgy, and brake pad compound capabilities...

[Leepz]

Howsit

Where can I get dot 5.1 brake fluid in Pretoria or JHB ?

[EX-DOHCTOR]

Too... much... reading... can't... go... on!