Since I tow a two car hauler periodically and live in Colorado, we have gained significant experience with brake fade with the stock brakes on the Ram and drum brakes on the trailer. The first steep hill we went down fully loaded into Bailey for club breakfast on the way to Gunnison, by the time we got to the tight right hand corner at the bottom we glided past the turnout because there was almost no brake at all.
This caused me to go study the mechanism that makes up brake fade.
Turns out there are two different major causes for brake fade. First is the build up between the pad material and the brake disk surface. As some brake pads heat up, they begin to outgas products from their manufacturing process. This gas creates an "air gap" between the pad surface and the disk surface. This type of fade can be addressed by selecting different pads that don't decompose during the higher heat of this demand loading. Slotted brakes help sweep away the built up layer of outgassing and holes in the disk increase the cooling surface area to potentially help lower the temperature of the disk.
The second type of brake fade is what I was experiencing. Brake fluid is hygroscopic. As soon as the fluid is exposed air - when you open the bottle of fluid or through the brake lines and the brake fluid reservoir- it sucks up water. The water does not mix with the brake fluid and instead being heavier than the brake fluid, migrates to the lowest points in the system. The lowest point in the system is generally at the brake pad where the actuator becomes contaminated with water. As you make high demands on the brakes, the disks and pads heat up, which in turn heats up the brake actuators at the wheel. The heat eventually causes the water in the fluid to boil and turn into a vapor. This is when the brakes "go away" because the incompressible brake fluid is pushing against a pocket of steam that is between the fluid and the actuator.
There are two key characteristics for brake fluid rating. Life span and operating temperature.
DOT 3 fluid is rated for THREE years life. After three years it MUST be changed. The reason it fails is because it absorbs enough water to become ineffective when you really need it.
DOT 4 fluid has a rating of TWO years. But it also has a higher operating temperature. The DOT2 boils at 284F while the DOT 4 boils at 311F
I have gone to DOT 4 and change it in all my vehicles every 2 years. For most of the Club cars we change it every 3 years with DOT 3 which is what the factory installs.
Their primary differences are their wet & dry boiling points and their composition.
| Dry Boiling Point | Wet Boiling Point | Composition |
DOT 3 | 205°C/401°F | 140°C/284°F | Glycol Ether |
DOT 4 | 230°C/446°F | 155°C/311°F | Glycol Ether/Borate Ester |
The stock brakes on the Kappa are very good but the pads are not designed to perform in extreme thermal conditions. I went with pad change on our cars and the performance was noticeably better. Since we started changing the fluid regularly, that has not been a continuing issue.