Brakes and Traction Control: Description and Operation

The function of hydraulic brake system is to transmit pressure from the master cylinder to caliper pistons. The system will operate properly if fluid is tight and brake fluid cannot be compressed. Normally, brake fluid cannot be compressed. If however the fluid overheats sufficiently it can partially change to a vapor form. Vapor can be compressed and since the master cylinder has a specific volume with which to build up pressure, the compression of vapor can result in excess brake pedal travel before the system has time to develop adequate braking pressure.
Brake fluid is hygroscopic in nature (absorbs water vapor from the air). For this reason it is important to keep brake fluid in a tightly sealed container. If only a small amount of fluid is required, it should be purchased in small cans. Avoid storing small quantities of fluid in bulk containers.
Only brake fluid which meets standard DOT 4 should be used. The boiling point for brake fluid depends on several factors including the ages of the fluid and climatic conditions. Any brake fluid efficiency will deteriorate as it ages. It should be changed at least every three years for cars in normal service.