I don't see any problem with your logic.
I agree that cutting the tube too short can cause problems. How short is too
short will vary with the actual distance that the bearing has to travel
before it releases the clutch. In my two installations this distance was not
the same. I don't remember the actual clearance between the bearing and the
pressure plate but it was within the specified parameters in both cases. I
do know that this distance was larger with the 1275 than with the 948. I had
to use a "very" modified carrier with the 948 just to get positive
clearance. With the 1275 I used the "normal" modified carrier.
With all parts being the same between multiple installations on a 1275 I'm
not sure why the "feel" would not be the same for all cases, assuming that
all push rods (MC and slave) were adjusted equal.
The variables would be the pressure plate and the flywheel itself. I know
for a fact that rebuilt (at least the one I tried) and new pressure plates
provide different measurement of distance from the rear plate. If the
flywheel has been modified it can also cause this distance to vary.
With Paul's installation you don't need to cut the tube but modifying the
flywheel does increase the clearance. I needed the 3/8" spacer between the
carrier and release bearing in order to get the correct clearance. The
spacer also has the effect of making the tube longer since it pushes the
bearing forward 3/8".
I'm not sure that any of this explains why the basic Rivergate installation
does not give the same feel to the clutch from car to car.
Larry Miller
----- Original Message -----
From "Jeff Boatright" <jboatri at emory.edu>
To: <spridgets@autox.team.net>
Sent: Thursday, April 20, 2000 2:48 PM
Subject: clutch feel musings
> 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/
>
|