I fail to see how using hydraulic pressure to actuate the clutch release will result in less lever pull than using a cable.
Ultimately, the force required at the clutch end must be applied at the lever end.
That statement is wrong. Neglecting friction, the universal law of conservation of energy dictates that the product of force x displacement (= travel) is constant. For the cable operated clutch,
looking at the clutch push rod and at the lever, and accounting for torque equivalenvce at the lever, we derive at
H * a / r = F2 * d2
where
a = pivot distance between hand's force point of attack and pivot point. For simplicity, I use the maximum radial distance between pivot point and lever blade (i.e., inboard of the sphere on a ball-ended lever).
r = pivot radius
H = force applied by fingers (please note it increases with travel)
F2 = force exerted by clutch rod end
d2 = maximum displacement at clutch rod end = "clutch lift".
The AMC clutch has 3 coil spings, and assuming perfect linearity, we have
F2 = 3 * k * (s+d2)
where
k = coil spring stiffness.
s = spring pre-compression displacement
Thus, we can predict that the lever pulling force H experienced by the rider is a product of coil spring stiffness, the required lift to free the friction plates within the clutch (depende on the area of friction), and geometric parameters "a" and "r" at the lever.
Late AMC bikes used these parameters:
r = 7/8" = 22.225 mm
a = 5.315" = 135 mm
Assuming the clutch remains stock (obviously it has a large potential for improvements, and the required lift is paramount),
H = 3 * k * (s+d2) * (d2) * r / a
reducing "r" by 10% and increasing "a" by 10% will reduce the pulling force H by 18% !
Fitting a different clutch with a larger friction area and lowering the spring stiffness will be much more effective though.
The AMC clutch may require a lift of 6 mm. A modern clutch with 30% more friction area may require a lift of 5 mm only to free the clutch stack. Let's assume the same clutch has 6 springs rather than 3, each with a spring stiffness of 40% of the stiffness of the AMC clutch,
and with the same pre-compression displacement (2mm assumed here), H will be reduced by a massive 42% !
Similar considerations can be made for a hydraulic operated clutch. The lever geometry differs though.
- Knut