"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)


I've seen a car somewhere which had a five-speed gearbox but the gears were
arranged as

R 2 4
1 3 5

rather than the more conventional

1 3 5
2 4 R


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? 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? 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?

In message m, Martin
Underwood writes

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? 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?
No bulk rings and no synchromesh Driving with a crash box is as natural
ordinary driving. It just takes a few hours practise.
--
Clive

"Martin Underwood" wrote in message
s.com...
"Bill Hayles" wrote in message
...

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

3 1
4 2

That's the way some of the Guy Arab utility double-deckers were set out.

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? 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? 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?

No synchromesh. If you do a clutchless change on a synchromesh gearbox, the
synchromesh cones will align the speeds if you are a little out of synch.

50 or 60 years ago, almost all cars had crash gears on bottom, and Rovers
had it on first and second gears, but they also had a freewheel, as I
recall. The Bedford OB, for example, had a crash gearbox, while the Dennis
Lancet III had a crash box on 1 to 4, but a pre-selector overdrive 5th
speed. Some were "constant mesh" gearboxes, where dog clutches engaged the
gears.
--
Terry Harper, Web Co-ordinator, The Omnibus Society
75th Anniversary 2004, see http://www.omnibussoc.org/75th.htm
E-mail:
URL: http://www.terry.harper.btinternet.co.uk/

"Terry Harper" wrote in message
...
"Martin Underwood" wrote in message
s.com...

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? 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? 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?

No synchromesh. If you do a clutchless change on a synchromesh gearbox,
the
synchromesh cones will align the speeds if you are a little out of synch.

Further to that, I worked with one driver on the East Kent whose method for
downchanges from 5th to 4th was to declutch and keep his foot flat on the
accelerator and the engine at governed revs. When the speed had fallen to 36
mph he snicked it into 4th. Most other drivers just kept their foot on the
floor and did the downward change at just over 36, with a pause as the speed
fell slightly. You can do the same on any governed engine with a synchromesh
box. With a petrol engine and no governor, like a Bedford OB, it doesn't
take long to get used to timing your changes. The "snatch" change from 1st
to 2nd on a steep hill is another matter.
--
Terry Harper, Web Co-ordinator, The Omnibus Society
75th Anniversary 2004, see http://www.omnibussoc.org/75th.htm
E-mail:
URL: http://www.terry.harper.btinternet.co.uk/

In message , Terry Harper
writes

50 or 60 years ago, almost all cars had crash gears on bottom, and
Rovers had it on first and second gears, but they also had a freewheel,
as I recall. The Bedford OB, for example, had a crash gearbox, while
the Dennis Lancet III had a crash box on 1 to 4, but a pre-selector
overdrive 5th speed. Some were "constant mesh" gearboxes, where dog
clutches engaged the gears.
I understood all crash boxes to be constant mesh.
--
Clive

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

"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.

In message m, Martin
Underwood writes
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)?
Cog meshing went out in the 1920s and since then it has always been
dogs.
--
Clive

"Clive" wrote in message
...
In message m, Martin
Underwood writes
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)?

Cog meshing went out in the 1920s and since then it has always been
dogs.

So, given that post-1920s gearboxes had permanently-engaged cogs, of which
one at a time was locked onto the shaft by dog clutches, why did it take so
long for manufacturers to add that other little refinement, synchromesh
cones?

"Martin Underwood" wrote in message
s.com...
"Clive" wrote in message
...
In message m, Martin
Underwood writes
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)?

Cog meshing went out in the 1920s and since then it has always been
dogs.

So, given that post-1920s gearboxes had permanently-engaged cogs, of which
one at a time was locked onto the shaft by dog clutches, why did it take
so
long for manufacturers to add that other little refinement, synchromesh
cones?

Just had a look in Alan Townsin's "The Bristol Story, Part 1", which has a
picture of a KS-type 5-speed gearbox, with its top cover removed, on page
58.

That had constant mesh 3rd and 5th gears, direct drive 4th gear, and sliding
mesh cogs for 1st and 2nd. It was superseded in the 1950s by a synchromesh
version.
--
Terry Harper, Web Co-ordinator, The Omnibus Society
75th Anniversary 2004, see http://www.omnibussoc.org/75th.htm
E-mail:
URL: http://www.terry.harper.btinternet.co.uk/