"Bill Hayles" wrote in message
...
The thought of having to drive a car without
synchromesh shares me ****less. As a matter of interest, how long did it
take to acquire the sixth sense of how much to blip the accelerator while
double-declutching to allow the new gear to engage?

Things are different now, but when I took my (car) driving test in
1968, many cars didn't have synchromesh, so you got used to it from
the start.

As recent as 1968? I thought all cars had synchromesh on all gears except
sometimes first and reverse (where it's less important, as you're unlikely
to want to engage first or reverse while moving) long before that.

One of the things we had to do to demonstrate our skill with a crash
box (on the bus, that is, not the car) was to show our ability to go
up and down the box without using the clutch. The philosophy was
that the clutch was a device for allowing the vehicle to stop and
start. Once you got the hang of it, it was surprisingly easy, and
is something I still do today.

I know that the Police driving manual "Roadcraft" makes reference to
double-declutching, and still recommends it even with a synchromesh box.
When I asked my IAM "observer" (instructor) his response was "that's a load
of archaic ******** [I'm paraphrasing!] - it's not necessary with a
synchromesh box and just slows your gearchanges down unnecessarily".

Why do rally-drivers use clutchless gearchanges? Is it quicker (ie less time
when the engine's not in one gear or the other)? Is this worth the risk of
muffing the gearchange, which would then take much longer?

With a synchromesh
gearbox, I've found the best way to do a clutchless gearchange is to
slightly over-rev the engine and let it slow down to the correct speed
when
the gear will engage under slight pressure on the gearlever; is the same
true of a non-synchromesh gearbox?

Not if you want to avoid a grinding noise.

OK, when changing down, you're describing *increasing* the engine revs until
the gear slips in whereas I was describing blipping the engine revs over and
letting them *decrease* until the gear slips in. Presumably the end effect
is very similar. Yours has the advantage that the engine revs are already
increasing, which is the direction you want them to go in when changing
down. I tried it in my first car (I wouldn't risk it in anything other than
a clapped-out car) and found it a very hit-and-miss affair.

Clutchless gear changes
in a fast revving car are different from on a slow, ponderous bus.
The technique when changing up was to lift the throttle, move to
neutral and, as the revs slowly dropped, to feel when the lever
wanted to drop into the next gear; you had a window of maybe a
second or so when it would go silently. Changing down was harder;
you couldn't get into neutral unless there was next to no driving or
over-run force. So you put your foot on the throttle and pushed on
the gear lever; it would drop into neutral. The revs would continue
to rise and at the right point the gear lever would move into the
next lower gear. In a car, this would all be over in a matter of a
second or so. On a Gardner diesel, you had all the time in the
world.

So very much the same technique as with a synchromesh gearbox. But... was it
as easy for the gear to engage when the engine revs matched if you didn't
have synchromesh? Do crash gearboxes actually engage the teeth of the
gearwheels or do they engage dog-clutches (ie like a synchromesh box except
without the synchromesh cones)?


FWIW, it was virtually impossible to change down without using the
clutch on a steep hill, as you were already at full throttle and
couldn't get out of the gear you were in without the clutch.


I presume no vehicles (cars, lorries, buses) produced nowadays have
non-synchromesh gearboxes.