In a message dated 97-06-09 18:59:01 EDT, JRHoffman@worldnet.att.net (Carol
Zingone) writes:
> Having read the recent thread on doubleclutching, can anyone give a
> description of what the benefit might be to a 74 TR6, with a rebuilt
> tranny, and how to actually perform this ?
Carol:
Many years ago, I drove a large Mack dump truck for a living. At that time, I
was not the giant of a man that I am now. I stood 5' 6", and weighed 112
pounds (I'm still 5' 6", but I've added a few pounds. OK, a lot of pounds).
In order to drive that beast, I had to learn to double clutch, and, often, to
shift without using a clutch at all. Perhaps a brief description of what
takes place during this manuever would be helpful.
When you are travelling along at a steady speed, or accelerating, the gears
on the input shaft are DRIVING the gears on the output shaft. The teeth on
the input gears are applying pressure to the output gear teeth. When you lift
off the throttle, and use the engine to slow the car, the gears on the input
shaft are now being DRIVEN by the gears on the output shaft. Now, the teeth
on the output gears are applying pressure to the teeth on the input gears.
During the transition between these two conditions, there is a period at
which no pressure is being aplied by or to either set of gears, and they are
rotating at the same speed. At this time, only the slightest force is
required to slip the transmission into neutral.
Once in neutral, the output shaft continues to rotate at the same speed as
before (at least until the car slows down). The input shaft is rotating at
engine speed. If you now rev the engine up to where the engine RPM nearly
matches the RPM it *WOULD BE* turning if it were in already in the lower
gear, the two shafts will now be turning at almost the same speed. Since they
are turning at the nearly the same speed, there would be very minimal
pressure applied to the gear teeth if the gears were to be meshed again.
Since it is impossible to exactly match the speeds, if you lightly press the
gearshift lever, the two gears will rotate till the teeth are in mesh, and
the transmission will readily slip into gear with no damage.
Of course, shifting up is the reverse of the above. You let the engine speed
drop till it matches the speed it will be at when in the higher gear.
With a little practice, except for starting from a stop, the clutch becomes
redundant. I don't recommend this method, but if you are having clutch
problems, or transmission problems, it can be a lifesaver. Combining this
technique, with the use of double clutching, significantly reduces the strain
on drive train components (and if you are a little guy driving a big truck,
it significantly reduces the strain on your left leg!).
Double clutching involves simply using the clutch to ease the burden of
getting out of gear, then releasing the clutch while you match the
engine/transmission speed. After you have matched the speeds, use the clutch
again to put the transmission into the new gear. By double clutching, it is
not as critical that the engine/transmission speeds match exactly. If you are
off a little, the gears still engage gently, with much less strain than
normal single clutching.
Driving the Mack was fun, but given my druthers, I'd druther drive an LBC!
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74
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