I can see how it would affect the pedal (causing sponginess and more travel toward floor), but how does it cause fade? Once you’ve compressed the air, the same pressure will then be applied to the caliper or wheel cylinder pistons.
I’m not seeing where the “fade” would come from.
It’s all about boiling points and compressibility of the fluid. Here’s a partial cut and paste from Federal Mogul about the issue…
Potential risks from old or contaminated brake fluid:
At high temperatures and with high moisture content, the water in the fluid can cause gas to be produced (vapor lock). As gas, unlike the fluid, can be compressed, there is no longer an optimum transfer of brake force. Braking power decreases and total brake failure can result. The basic rule of thumb is: the lower the wet boiling point, the greater the risk of brake failure. So it is important to follow the manufacturer’s recommendations for the brake fluid and to have the brake fluid regularly checked by a specialist workshop.
OP? Hello? Year, Make Model Mileage of your vehicle please…
Brake fade also happens as the pads overheat and gas off, basically pushing the pad off the rotor and killing the brake power. Once the pads have a chance to cool and recover, brake function returns. Drilled and slotted rotors resist this by giving the off gas a place to go.
There is not enough travel in the pedal or the master cylinder to compress air to the point where it would move the hydraulic fluid enough to apply any effective pressure to the brakes.
Fluids are pretty incompressible, gasses are very compressible. Your torque converter wouldn’t be able to move your car if you replaced the transmission fluid with air.
Thanks for the comments It now makes sense. I’ll try a couple of your suggestions. My wife just wanted me to increase the life insurance.
She’s a very practical woman, @Norts.
“Your torque converter wouldn’t be able to move your car if you replaced the transmission fluid with air.” Off topic here, but propulsion has nothing to do with the compressibility of the fluid, which is a general term that includes liquid and gas. Propulsion by fluid has to do with the mass of the fluid being moved. And to move a huge mass of fluid, you need either high speed or a large machinery moving a huge area of fluid. You can have air torque converter if your engine happens to spin at 5 or 6 digit speed, which would not be very efficient. Combine speed and a ten feet diameter fan, it can propel a 747.
Yes and you can build a boat with an air propeller instead of a water propeller but it will need a much larger diameter because… The air is much less compressible than the water.
Actually, you need a larger propeller with air because air is so much less dense than water. An air propeller doesn’t really compress the air much at all.
@oldtimer11, @chunkyazian, just look at the difference in a motor boat screw and an air boat prop to see the difference between air propulsion and fluid propulsion.
I know liquid propeller generally has a smaller diameter than air propeller, but that’s due to the density, not compressibility of air. Compressibility of air is negligible at flow velocity below Mach 0.3
Air compresses much more than brake fluid. The calipers can’t push as hard against the rotors and braking is reduced.