[Mart]

1ton said it is heat related. that's true. All brakes get hot when used. the fluid warms up and expands. When the brakes are released there is an open port (the recuperation port) that allows fluid pressure to equalise between the system and the reservoir. When you press the pedal, the very first part of the travel closes this port, allowing you to pressurise the system and apply the brakes. you might sometimes observe a little squirt of fluid into the reservoir as you apply the brake pedal, that is coming from the recuperation port.

If the pushrod is too long the port is already closed and the fluid can't equalise before the brakes are applied. The heat from the brakes further pressurises the system and applies the brakes even harder. I't's a vicious circle.

If the pushrod is too short, you get a lot of lost motion before the brakes are applied.

The trick (and I have done this) is to fine tune the pushrod length so you minimise the lost motion but still maintain an open port at rest.

the other important thing is to ensure the brake pedal has a good return spring so it returns to the up position cleanly. If not, you could have a similar scenario where the recuperation port is not open.

Mart.