This high-rate spring is what causes such a vague and disconnected clutch pedal feel. The clutch pedal travels in a circular arc, with the spring assist in the middle of that clutch pedal travel. The middle of that motion compresses the spring initially and then allows it to extend after the first 30 degrees of travel. The combination of a high-rate assist spring and motion of the pedal during engagement causes a non-linear and sometimes confusing pedal feel. Having a non-linear pedal feel makes it hard to modulate the clutch on your S197 Mustang. Steed's ever so popular S197 Clutch Spring Assist is now available with a Heavy Duty Spring Perch assembly, therefore eliminating the worry of you breaking the factory one upon installation or removal.