Rob Graham wrote:
On 05/02/2010 13:48, Douglas Payne wrote:
Dave wrote:
Rob Graham wrote:

That's what I thought of at first but you'd lose power steering and
servo-assisted braking.


I'm now informed that modern cars' engines won't go faster than a
certain amount, so won't blow up. In which case, going into neutral
would be fine.

I'm sure even engines before the advent of fuel injection will run for a
little while at a mechanical limit of revs which is set by the standards
of engineering in the engines internals. (c:

A friend's wife was driving their 1985 Merc when the accelerator linkage
popped off and she was left with a racing car. Although the vehicle was
not exactly new, it was injection. But I don't know whether it was
governed to a maximum speed. If I'd been driving it I'd have turned it off.

Brake servos on petrol cars are generally powered by the vacuum from the
engine sucking against the throttle butterfly in the inlet manifold. If
the throttle is open (engine running or not) the servo has no vacuum to
power it. What's stored in the servo for the power assistance may not
last as long as it takes to stop.

It takes a LOT more effort to stop a car designed with power assisted
brakes when the assistance is not functioning. That would add to the
panic in a runaway situation no doubt.

--
Douglas

Adrian C wrote:
On 05/02/2010 13:48, Douglas Payne wrote:


Power steering would work fine with the car in gear engine on or off as
long as its not a clever electrically powered system, and anyway, the
steering would just go heavy, not immovable with a loss of power.

Problem is that on some cars like the new Mini, manual steering is
unfortunately a bit on the heavy side of heavy.

http://www.bbc.co.uk/blogs/watchdog/..._failures.html

Sure, the Steering on my MX-5 can't be much more than 2 turns lock to
lock. Without assistance the wheel still turns though, and at motorway
speeds failure of the assistance would be noticeable but the car would
still be eminently steerable.

Parking would need some fairly serious effort.


Dunno what the answer is.


Eject a boat anchor out of the boot ...

Why don't the government do something!

--
Douglas

Dave Plowman (News) wrote:
In article op.u7ncurd1haghkf@lucy,
Duncan Wood wrote:
~I've yet to see a keyless ignition you can't turn off, or a Toyota
that wouldn't stop if you stood on the footbrake in 5th.

Indeed.

Don't know of any car which has such poor brakes. It would be
positively dangerous.

Check Autocar's figures for braking versus acceleration. You won't
find any car which can accelerate more quickly than it can brake -
and that's through the gears, not in fifth.

Yeah but, how about an automatic? If the throttle is jammed open then I
imagine as the vehicle speed drops, the box is going to react as if you've
hit a fecking big hill and start dropping cogs.

Could you stop a car at full throttle in first gear say? Add the possible
effect of reducing servo assistance with a wide open throttle and brake fade
(which I think could come on very quickly in those circumstances) it might
well not be possible to stop a full throttle auto with the brakes alone.

Does anyone know if there are any autos that *can't* be forced into neutral
whilst under load? Evidently some owners are under the impression that this
can't be done.

Tim

In article ,
Douglas Payne wrote:
I'm now informed that modern cars' engines won't go faster than a
certain amount, so won't blow up. In which case, going into neutral
would be fine.

I'm sure even engines before the advent of fuel injection will run for a
little while at a mechanical limit of revs which is set by the standards
of engineering in the engines internals. (c:

Indeed - you get valve 'float' on most which limits the maximum revs.

--
*The only difference between a rut and a grave is the depth.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Tim wrote:
Check Autocar's figures for braking versus acceleration. You won't
find any car which can accelerate more quickly than it can brake -
and that's through the gears, not in fifth.

Yeah but, how about an automatic? If the throttle is jammed open then I
imagine as the vehicle speed drops, the box is going to react as if
you've hit a fecking big hill and start dropping cogs.

Yes.

Could you stop a car at full throttle in first gear say? Add the
possible effect of reducing servo assistance with a wide open throttle
and brake fade (which I think could come on very quickly in those
circumstances) it might well not be possible to stop a full throttle
auto with the brakes alone.

I'd say it still would on one with half decent brakes.

Does anyone know if there are any autos that *can't* be forced into
neutral whilst under load? Evidently some owners are under the
impression that this can't be done.

Don't know of any. My BMW has a computer controlled auto and you can on
that.

--
*The longest recorded flightof a chicken is thirteen seconds *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:

Indeed - you get valve 'float' on most which limits the maximum revs.

I bought an 8v Punto, and there's really no question of it needing a rev
limiter. Just as well, considering what the kids do to it.

--
Electric cars are very healthy - when the battery runs out you have to
walk home.

On Fri, 05 Feb 2010 13:32:21 -0000, Conor wrote:

In article , Dave says...

That's what I thought of at first but you'd lose power steering and
servo-assisted braking.

And? You can still steer and stop.



If you leave it in gear & turn the ignition off you won't lose either.
Even if you do the you won't lose the servo unless you pump the brakes.

Duncan Wood

On Fri, 05 Feb 2010 16:10:10 -0000, Douglas Payne
wrote:

Rob Graham wrote:
On 05/02/2010 13:48, Douglas Payne wrote:
Dave wrote:
Rob Graham wrote:

That's what I thought of at first but you'd lose power steering and
servo-assisted braking.

I'm now informed that modern cars' engines won't go faster than a
certain amount, so won't blow up. In which case, going into neutral
would be fine.

I'm sure even engines before the advent of fuel injection will run for a
little while at a mechanical limit of revs which is set by the standards
of engineering in the engines internals. (c:

A friend's wife was driving their 1985 Merc when the accelerator
linkage popped off and she was left with a racing car. Although the
vehicle was not exactly new, it was injection. But I don't know whether
it was governed to a maximum speed. If I'd been driving it I'd have
turned it off.

Brake servos on petrol cars are generally powered by the vacuum from the
engine sucking against the throttle butterfly in the inlet manifold. If
the throttle is open (engine running or not) the servo has no vacuum to
power it. What's stored in the servo for the power assistance may not
last as long as it takes to stop.

It takes a LOT more effort to stop a car designed with power assisted
brakes when the assistance is not functioning. That would add to the
panic in a runaway situation no doubt.


But unless you pump the brakes you won't loose the servo assist. If you
turn the engine off the pedal doesn't rise up under your foot.

--
Duncan Wood

Douglas Payne expressed precisely :
Brake servos on petrol cars are generally powered by the vacuum from the
engine sucking against the throttle butterfly in the inlet manifold. If the
throttle is open (engine running or not) the servo has no vacuum to power it.
What's stored in the servo for the power assistance may not last as long as
it takes to stop.

If the pedal is pressed and kept pressed, it will use up a minimal
amount of vacuum. However repeatedly pressing and releasing could use
up all of the vacuum. Test it - climb in the car and without starting
it press the brake several times. Assuming there is no fault in the
servo, you should be able to press it four of five times before the
vacuum is exhausted.


It takes a LOT more effort to stop a car designed with power assisted brakes
when the assistance is not functioning. That would add to the panic in a
runaway situation no doubt.

One of the suggestions is to knock it out of gear - that cannot usually
be done when the car is accelerating or decelerating, unless the clutch
is pressed. Pressure on the gears keeps it in gear.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

Tim laid this down on his screen :
Yeah but, how about an automatic? If the throttle is jammed open then I
imagine as the vehicle speed drops, the box is going to react as if you've
hit a fecking big hill and start dropping cogs.

I checked this out for a completely unconnected reason about twelve
months ago on my auto and yes I can most certainly bring it to a stop
from in excess of 70mph.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk