What causes my brake pedal to ‘go long’?
Aside from mechanical failures, most cases of long brake pedal are caused by boiling brake fluid in the brake caliper. When the fluid is overheated, the resultant gas bubbles can compress, and this causes the long pedal.
Most people will be aware that brake calipers have pressures seals in them to keep the brake fluid inside the caliper. These seals end up with a very small amount of brake fluid behind them that is forcing the pistons to push the pads – and hopefully slow your car! What many will not realise is that it is this very small volume of brake fluid that takes most of the punishment from the sometimes very high temperatures in a brake system. Also, this small amount of fluid does not really circulate around the caliper much. So it gets repeated temperature cycles and will deteriorate and be less able to deal with temperature if not replaced regularly.
The other reason to replace your fluid regularly is the fact this type of fluid is hydroscopic (will absorb moisture) so over time will have higher content of moisture, causing the boiling point to reduce.
Make sure your brakes are bled regularly, particularly after copping a hard time at the track or in the forest) and always choose a high-quality fluid such as the Circo MF1200+ to give yourself the best chances or avoiding the dreaded long pedal.