[Vwdiesel] Quantum Milage pre & post re-ring

[Tad]

Just my two cents/experience - after 9 years and almost 160k miles of fairly
extensive downshifting on my 01 Golf TDI I changed the clutch, and it still
had some life left in it.  In that time I've changed the rear brakes 3 times
(once due to a stuck caliper) and front brakes are *still original* with
maybe 40-50% left!  I think that's pretty good proof for me that the
wear-on-the-clutch argument doesn't hold much water.  Does it cause
additional wear?  Yes, but very, *very* little.  I'm far enough from my
college physics that I can't actually do the math, but I would bet dollars
to doughnuts that the amount of friction required between the clutch and
flywheel in order to spin a warm engine from 1000 to 3000 RPM (or so) is an
order or magnitude less than what it takes to, say, start out in 1st on
level ground.

Also I wonder about the accuracy of the JC Whitney MPG unit - I don't recall
what car Bill drives but my understanding is that any electronically fuel
injected car (gas or diesel) will totally cut fueling when in "overrun" -
the condition where the engine is being driven by the wheels such as when
coasting down a hill.  Logic would dictate that burning any fuel to idle the
engine while coasting would be greater than burning zero fuel while in
overrun - the only question would be whether you'd then use more fuel
regaining any lost momentum vs not engine braking.

As far as worn synchros go, I have also seen that on some worn-out beaters
(usually on 2nd gear, probably because that's the most-often-downshifted
gear), but I remember reading somewhere that VW reinforced the 2nd gear
synchros on the 02M tranny for that very reason.

Now as for which is "better" - it's just personal preference really.  For
me, it's "just the way I was taught" by my truck-drivin' daddy. :)  One
could certainly argue that it's safer to downshift - any emergency maneuver
requiring acceleration (or deceleration for that matter, if your brakes
happen to fail) is a second or two further away if you're in neutral vs in
gear and technically (at least in Oregon) it's actually illegal to operate
your car in neutral.

On Thu, Oct 7, 2010 at 11:03 AM, Erik Lane <eriklane at gmail.com> wrote:

> Yes, by downshifting you're saving wear on your brakes, but you're
> increasing wear on the clutches inside your tranny. They are metal
> cone clutches, so they will generally last pretty well, but it's
> really a good idea, in my opinion, to use the brakes for what they
> were made for. Sure, if you have a very long downhill you can
> downshift and use the engine, but in general downshifting puts extra
> wear on tranny parts. It's much easier and cheaper to do brake work
> than tranny work!
>
> So I would suggest using the brakes as the default, but using the
> engine for prolonged things. But when you do downshift it is nicer to
> double-clutch it to put less wear on the internal transmission parts.
>
> Just something to think about.
>
> Erik
>
> On Thu, Oct 7, 2010 at 2:45 AM, William J Toensing
> <toensing at wildblue.net> wrote:
> > Since 1996, all new cars sold in the USA have to be OBD 2 compliant which
> means that any car must have a standardized plug that you can plug in an OBD
> 2 reader to find any problems stored on the car's computer. Mark, I don't
> know if this applies to cars sold in the UK. The reason I mention this is
> that I bought an MPG meter that plugs into the OBD 2 port on my 2001 Focus
> from JC Whitney. The brand of the meter is Kiwi & it is made in Calif., not
> China. It has several functions, of which one reads average MPG & another
> reads instant MPG. It is interesting to watch MPG readings while
> decelerating. If I put the car in neutral & use the brakes to stop I get
> readings of 150 MPG. If I slow down while in top gear or 5 th gear, MPG will
> run from 90 to 120 MPG. If I shift into 3rd using the engine to slow down,
> which I often do, MPG is around 45 MPG. Observation: For maximum MPG, when
> braking, put the gear box into neutral & use the brakes to slow down.
> Shifting the gear box into a lower gear to avoid using the brakes results in
> a lower MPG, but does save on brake pads. I can see how a Prius gets 50 MPG
> (USA) because it can recapture energy used in braking.
> > Bill Toensing
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