Re: synchro problems and brake pedal height

[Simon Favre <favres@engmail.ulinear.com>]

>From before:

>>I assume you mean a double-declutch. Just blipping the throttle will only
>>help if the clutch is sticking, which should better be repaired.
>
>Good point, Einar!  Tapping the gas pedal shouldn't have any effect on
>the speed of the gearbox input shaft, since the clutch is engaged.  I
>meant double-declutching and tapping the throttle.  Or maybe some people
>call the scenario described in the previous sentence
>"double-declutching"?

True, but most clutches drag just enough that blipping the throttle with
the clutch pedal depressed still helps.  Double-clutching and double-
declutching are the same thing depending only on local lingo.  You step
on the clutch, shift to neutral, release the clutch, blip the throttle,
then step on the clutch and engage the lower gear.  Done properly, the
lever will just drop into the lower gear neat as you please.

>>But on my GTV 2.0 the brake pedal is too low to make this convenient.
>>Is this normal, or is there some adjustment I have to do?
>
>I'm not sure why you bring the brake pedal in the picture, so I'm not
>the one to answer the question.

The reason is that during a downshift, you are usually slowing down,
hence the foot partly on the brake.  The racer's among us refer to this
as heel-and-toe driving.  Shankle sells a hell-and-toe kit for the Spica
equipped cars to set the height of the pedals to make this easier.

>>The high momentum of the driveline also opposes a quick gearchange using
>>double-declutch,
>
>Do you think the driveline has a high momentum?  It's long indeed, but
>not too much mass away from the axis of rotation, and that's what
>increases the momentum.  It might not add much compared to the flyweel.

The driveline has a HELL of a lot of angular momentum.  Have you ever
held an Alfa 2nd gear in your hand?  They are huge, and weigh a ton for
such a small car.  That's why racers routinely lighten the gears.
Remember, you have to spin ALL of them up to speed just to match speeds
on ONE of them.

>And since we are talking synchros, can somebody explain why Alfas have
>problems only with 1st and 2nd gear synchros.  Why not 3rd and 4th,
>since 
>...

The problem with 1st has already been described.  Basically, the Alfa
engineers, in their *infinite wisdom* decided you only needed half a
synchro on 1st.  There are actually 2 problems with 2nd.  Traditionally,
Alfa used a fairly large ratio gap between 2nd and 3rd.  That means that
downshifting from 3rd to 2nd requires more work from the synchro, or a
bigger blip on the throttle to match speeds.  This extra work can make
the synchro on 2nd wear out first.  2nd also sees a lot of shifting
around town.  The other problem IS the inertia.  Apparently, the old 101
series 4-speeds did not have as much inertia, and shifted quite easily.
When Alfa added the 5th gear, they added quite a bit of mass to the
countershaft.  The 5th speed gearwheel is small, but the mating one on
the tail end of the countershaft is massive.  Remember, the countershaft
is always spun by the input shaft.  Again, this is why a professionally
lightened gearbox is such a welcome change for the "modified" crowd.

Steel flywheels can be lightened to improve engine "revviness" without
compromising street driving.  Aluminum flywheels can make a car almost
undriveable on the street.  They also may not last as long on the road.
Racers use them because they don't have to get going from a dead stop
more often than once a race.  They also don't put as many miles on a
car, and they tear them down a lot more often.