Hydro-Boost Manual
When reserve power is depleted (manual operation) pressure on the brake pedal will cause the input bracket to separate from a shoulder on the input rod, compresses the input spring and allows a change of ratio between input and output rods. This ratio increase will cause the brake pedal to travel further and increases the mechanical force applied to the master cylinder.

For disassembled photos, see this post.

Owner caption January 2006 · Photo 1158 of 5000