Date:         Wed, 22 Jul 2009 08:43:23 -0400
Reply-To:     pdooley <psdooley@VERIZON.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         pdooley <psdooley@VERIZON.NET>
Subject:      Re: Friction
Comments: To: Larry Alofs <lalofs@GMAIL.COM>
In-Reply-To:  <96c89c360907220438u3bda5ce7xb5a51a409ca23fd3@mail.gmail.com>
Content-type: text/plain; charset=us-ascii

Don't forget what was mentioned earlier regarding the diaphragm pressure.
Depressing the clutch pedal loads up the engine's thrust bearing with
significant force.
Exactly how much of that force translates into friction, I'm not sure.

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Larry Alofs
Sent: Wednesday, July 22, 2009 7:38 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Friction

Interesting question, more complex than I thought at first.
  With the trans in neutral, depending on the design of the MT, there
is still some frictional coupling between the input end and the out
put end, depending also on the viscosity of the lube.  In most MTs I
believe this would tend to make the two ends turn at the same speed as
if it were in high gear (straight thru).
   Assuming that the clutch pedal is not depressed, the viscous
coupling in the trans could then either help or hinder the coasting of
the vehicle depending on its speed and the rpms of the engine.  If the
vehicle is moving fast and the engine is idling this effect would slow
the vehicle slightly.
   If the clutch is depressed, the engine speed is not important.
There will still be some frictional drag as the output end of the
trans turns or tries to turn the input end.  The frictional energy
loss at the throwout bearing is not relevant because it is just the
engine vs. the clutch fork.
   Now of course if the clutch doesn't release completely.....ugh, too
complicated for this early in the morning.