Ford 2007 WQ Fiesta Repair Manual page 210

206-0214 Drum Brake 206-02-4
DESCRIPTION AND OPERATION
The heat generated during braking is passed to
the bi-metallic strip. If the heat exceeds a critical
point, the bi-metallic strip bends upwards into the
corresponding nib and prevents further adjustment.
After the brake has cooled again, the bi-metallic
strip returns to the initial position. Adjustment is
now possible again.
2006.0 Fiesta
1212006 G250944en