I've recently installed a Rivergate 5 speed conversion. My clutch
'feel' is actually better than I had prior to the conversion, though
I have not driven the car enough to get a good feel for how much of
the pedal motion is actually used in moving the release bearing
forward to and then against the pressure plate contact surface.
I had some thoughts about clutches and what I think of as clutch
"feel". I'd like to know what you think about this.
When working the release fork by hand (tranny on bench), it occurred
to me that the entire motion of the clutch pedal should be composed
of play in the pedal bushing, play in the MC push rod set-up, play
between the slave cylinder push rod and outer fork end, play between
the inner fork end and the release bearing carrier, movement of the
carrier down the tube (another way of saying play between the release
bearing and pressure plate contact surface), and finally, the
distance that the fork pushes the release bearing into the contact
surface to disengage the clutch entirely from the flywheel.
Out of all these components, I assume that the last one, that point
at which the release bearing starts to push against the contact
surface to the point at which the clutch is completely free of the
flywheel surface, is mainly what a person "feels" as clutch
engagement or disengagement. As such, the snappish clutch feel that
many associate with these Datsun conversions is really a function of
the moment arm of the release fork. That is, imagine a situation
where the outer arm of the fork (the part of the fork from the slave
push rod up to the pivot point inside the tranny housing) is very
long and the tines of the fork (from the pivot point to the pads that
contact the back of the release bearing carrier) are very short.
There would need to be a lot of motion in this set up to move the
release bearing into the pressure plate contact surface. This would
result in a clutch that has a "feel" of gradual take up of friction.
Pressing the clutch pedal to the point of disengagement would take
little pressure but quite some distance, and conversely, releasing
the clutch would be light but again would take a lot of motion. Now
imagine the opposite situation, with a short outer arm and very long
tines. A little motion of the fork outer arm would translate into a
lot of motion at the tines. Hence, disengaging the clutch would take
a lot of effort (a lot of pressure on the clutch pedal) over a very
short distance. Conversely, in engaging the clutch (pulling your foot
off the clutch pedal), the pedal would be pushing hard against your
foot and would only have to move a little distance before the clutch
plate is fully pressed against the flywheel. This would give a
"snappish" clutch.
Is this wrong-headed?
Jeff
Jeff Boatright '65 Sprite MkIII __o_\__
http://userwww.service.emory.edu/~jboatri/
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