On Sat, 19 Jun 2004 17:05:09 GMT, "Martin Underwood"
wrote:


"Bill Hayles" wrote in message
.. .
On Fri, 18 Jun 2004 16:12:41 +0100, Clive
wrote:

Just to complete the picture from that (my) era, the GS class was
the only LT bus with a crash box, which worked back-to-front (just
like the Citroen "H" van I once owned).

When you say "back to front" do you mean that the layout was:

3 1
4 2

(ie a left-to-right switch of the gear positions)

or

2 4
1 3

(ie a top-to-bottom switch of the gear positions)

Neither.
4 2
3 1

i.e. first where you'd expect fourth.



When people refer to "crash gearbox", do they literally mean one without
synchromesh (ouch!) or just a manual gearbox as opposed to a pre-selector,
clutchless or automatic?

(a bit of self promotion; some of this can be found at
http://billnot.com/lcbs/index.php
)


(Very brief bit of history may be in order. In 1970, what was the
London Transport Country Bus Division was hived off to become London
Country Bus Services, inheriting all of LTs country bus fleet, hence
the mixed LT /LCBS attributions)

I was driving true crash (although LT and LCBS always called them
"clash") box buses until 1978 - The Royal Blue / Bristol LW6G, which
LCBS hired during a time of shortage. These buses were built in the
mid 1960s.

The GS (referred to above) was also a crash box, London Transport's
last.

At LCBS, we were also taking delivery of some awful small Bristol
single deckers with synchromesh manual boxes: many of us preferred
the crash boxes on the older buses.


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.

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


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. 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 slow. On a Gardner diesel, you had all the time in the
world.

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

Thanks for the nostalgia trip!

--
Bill Hayles

http://billnot.com