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Date:         Wed, 22 Jul 2009 07:00:27 -0700
Reply-To:     Don Hanson <dhanson928@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Don Hanson <dhanson928@GMAIL.COM>
Subject:      Re: Friction
Comments: To: pdooley <psdooley@verizon.net>
In-Reply-To:  <0KN6005PQOOA8IS3@vms173015.mailsrvcs.net>
Content-Type: text/plain; charset=ISO-8859-1

From personal experience (I often shove my 5sp into neutral as I approach stop signs, negotiate off-ramps, descend grades) I'd say there is not much difference in friction. But it's more comfortable to not have to hold down the clutch pedal and it's probably a bit less wear on the throwout bearing. Also, not many drivers are skilled at 'Heel/toe" (simultaneous braking and throttle control ) so just letting out the clutch without matching the RPMs to the speed of the driveline (when you get ready to use the motor's power again) is likely tough on the clutch. It can also cause vehicle control issues if one is not familiar with the dynamics of traction and is operating close to the limits, then 'pops the clutch' in the middle of a turn, etc. One can see some improved mileage by carefully coasting at appropriate times..Though I am sure the Lawyers and the Car manufacturers, the DOT and everyone else will tell you "Never never never coast...it's dangerous" or some such thing... I do it all the time but YMMV....Your mileage may vary...and since this is the US...I will say Don't try this....sheesh. Don Hanson

On Wed, Jul 22, 2009 at 5:43 AM, pdooley <psdooley@verizon.net> wrote:

> 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. >


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