RE: double clutch

["Weiss, Jeffrey" <jeffrey.weiss@domain.elided>]

Gregory S. Youngblood points out:
>> David gives the short explanation:
>>> Double clutching helps weak synchronizers, straight cut/
>>> racing gears and old non-sychro transmissions engage without
>>> crunching. Otherwise you'll have to quickly match gear speed
>>> /engine RPM by ear, which takes longer to learn....
>>
>> [Me:] "Otherwise"?  I don't see how one is a substitute for the
>> other.  You can't match gear speeds with the engine unless you
>> double clutch,  so don't you really have to do both?
 
> I don't know about Alfas, but after driving some cars long
> enough you "just know" the point to shift up and down and
> matching speeds by ear. As an exercise in being cocky (was a lot
> younger and stupid) I used to often shift up and down while
> driving without using the clutch at all.

Yes, but that's exactly the point.  When not using the clutch,
the input side of the tranny is attached to the engine.  You can
then match the input side to the output side by matching engine
speed with the driven side speed, and you can develop the "ear"
or the "timing" to get it right.  Been there, done that.  It's a
good skill to have in your toolkit "just in case."

However, if you use the clutch and only singly-clutch (or, more
specifically, "declutch"), then the tranny is disconnected from
the engine and you can't match the tranny input side to the
driven wheels side by using the engine.  Your ear is also not
likely to be able to discern the spinning input shaft amongst
other sounds - your only tool is getting used to the time it
takes for the input shaft to spin down.

> Question, if the clutch isn't used to shift, do the synchros 
> still work to make the shift smooth? Back when I did this, if I
> screwed up I'd grind the gears, so I've just assumed that the
> syncros weren't getting used that much, if at all.

Well, they'd like to help, and they're there as always to do the
job.  Problem is that they can't spin anything up or down to
speed because all parts of the tranny are connected to something
considerably more influential than them (i.e., engine and wheels).
So, in effect, they don't work, except to put pressure on the
shifter letting you know they're not pleased.  If you use the
right touch (as pointed out by Mark), the syncros will let you
know when speeds match well.
--
jw
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