The brake fluid you use is directly related to how your brakes will perform, but this fluid is often the most neglected maintenance item in a daily driven car. Neglect the maintenance of this fluid on the track and you will learn in a hurry how important it really is.
Brake fluid is simply hydraulic fluid…. An uncompressible fluid used to transmit force to the brake piston acting on the pad. Brake fluid is a fragile fluid. Brake fluid is hygroscopic which means it will absord water. If the brake fluid gets too hot it boils.The more water the brake fluid contains the lower the boiling point. If you boil the fluid you form bubbles of water vapor which are very compressible. The fluid no longer has the ability to transmit braking energy from the pedal to the caliper. The pedal goes soft and your ability to slow the car is compromised.
Air trapped in the line is also compressible and will cause a soft pedal all the time not just when hot.
In order to keep this from happening at the track you should at minimum bleed your brakes until the fluid runs clear. If your brake fluid is more than 6 months old it should be changed even if the car was never used. As it sits the fluid is absorbing water vapor from the air. How much? I don’t think anyone knows. But just to be safe it’s a good idea to use fresh fluid.
The type of fluid you use will ultimately be determined by your vehicle owners manual, but for the purpose of this article we will assume a modern car which operates on DOT type 3 fluid. DOT type 4 fluid is interchangeable with DOT 3. DOT 4 brake fluids have higher dry boiling points, but are unfortunately more hygroscopic than type 3 which is why it needs to be changed often. Don’t attempt a road course on DOT 3 fluid. It just won’t perform well.
Popular fluids for track days are ATE Super Blue which is relatively cheap at about $12 per liter. It’s dry boiling point is 536F, and it’s wet boiling point is 392F. MOTUL RBF600 is the next step up and is $20 per ½ liter. The dry boiling point is 593F, and the wet is 420. So even when it’s completely saturated it’s got a higher boiling point than the ATE Super Blue.
Brake fluid is simply hydraulic fluid…. An uncompressible fluid used to transmit force to the brake piston acting on the pad. Brake fluid is a fragile fluid. Brake fluid is hygroscopic which means it will absord water. If the brake fluid gets too hot it boils.The more water the brake fluid contains the lower the boiling point. If you boil the fluid you form bubbles of water vapor which are very compressible. The fluid no longer has the ability to transmit braking energy from the pedal to the caliper. The pedal goes soft and your ability to slow the car is compromised.
Air trapped in the line is also compressible and will cause a soft pedal all the time not just when hot.
In order to keep this from happening at the track you should at minimum bleed your brakes until the fluid runs clear. If your brake fluid is more than 6 months old it should be changed even if the car was never used. As it sits the fluid is absorbing water vapor from the air. How much? I don’t think anyone knows. But just to be safe it’s a good idea to use fresh fluid.
The type of fluid you use will ultimately be determined by your vehicle owners manual, but for the purpose of this article we will assume a modern car which operates on DOT type 3 fluid. DOT type 4 fluid is interchangeable with DOT 3. DOT 4 brake fluids have higher dry boiling points, but are unfortunately more hygroscopic than type 3 which is why it needs to be changed often. Don’t attempt a road course on DOT 3 fluid. It just won’t perform well.
Popular fluids for track days are ATE Super Blue which is relatively cheap at about $12 per liter. It’s dry boiling point is 536F, and it’s wet boiling point is 392F. MOTUL RBF600 is the next step up and is $20 per ½ liter. The dry boiling point is 593F, and the wet is 420. So even when it’s completely saturated it’s got a higher boiling point than the ATE Super Blue.
The ultimate in brake fluids are ester based. These include Castrol SRF, Endless RF650, AP Racing 600 and Brembo LFC600. Endless RF650, Brembo and Castrol are used exclusively in Formula 1 & Porsche GT3Cup cars. 1 liter of these brake fluids costs about $60-$80. Yeah… you read that right.
Boiling Points dry/wet in farenheit:
Brembo LCF 600: 600/399
Endless RF 650: 622/424
Castrol SRF: 590/518
Motul 660: 617/400
Wet boiling point on the Castrol SRF is impressive and significantly better than all others. You can see that Castrol didn't lose much performance between dry and wet. If you want the ultimate these are your choices but overkill for anyone reading this post.
I stick with the MOTUL RBF600 and bleed 1 liter through all 4 calipers before each track day. I have never had a problem with fade. Make sure there is no air coming out of the bleed screws before moving to the next caliper. Use a pressure bleeder for quick and easy bleeding.
No comments:
Post a Comment