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new defender
automatic
Change
for the better
Defender auto conversions have been around for years – but never like this.
Ed Evans reports on a new Defender 2.4 with electronic auto transmission
W
PHOTOS: SIMON HIPPERSON
ere in the thick of Luton’s
traffic, skimming around
three-lane roundabouts and
powering away from traffic lights with
the best of them. Inside the Defender’s
cab, the atmosphere is relaxed but for
the occasional surge of the torque
converter as it spins the power from the
tuned 2.4DCi engine through a superslick automatic gearbox.
A 2007 Defender should have a sixspeed manual gearbox that has you
stirring gears every few revs for the sake
of reduced emission levels. But that
gearbox is under the bench back at
Ashcroft Transmissions’ workshop.
In its place, we’re having great fun
with the company’s latest conversion:
a four-speed electronically controlled
auto box that’s so smooth, you’ll forget
there’s even a gearbox there.
But this conversion is no simple
component swap. It’s taken months of
painstaking design engineering and the
co-operation of specialist companies to
mate the ZF automatic gearbox to the
latest Defender’s Ford-derived engine.
We’re long past the era of simple outand-in conversion jobs – the trick today
is in orchestrating the engine and
transmission electronically, and
Ashcroft and its engineering colleagues
have gone overboard to match these
units and give the driver full control of
how the gearbox will perform.
In basic modes, this set-up has all the
competency you’d expect in a Discovery
3: full auto, semi-auto ‘sport’ flick-shift
and manual hold. But the Defender
deals with extremes, and that demands
an extreme transmission that’s fully
programmable by its driver – a bespoke
transmission with characteristics that
can be altered at will.
Set your own individual gearchange
speeds; control the hydraulic pressure to
set fast or gentle gearchanges; have the
torque converter lock up when you want
it to. It all adds up to a gearbox that can
be programmed for optimum off-road
performance, best towability, easiest
town driving, sports acceleration or
even the mood of the driver. All that,
and you can watch it happening on the
programmable control/display unit.
And it gets better. Even the 2.4 4cyl
Ford diesel has been tinkered with – or,
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for normal run-out tolerance of 0.005-inch
between engine and transmission.
A new bellhousing (strictly, a torque
converter housing) was designed to mate the
ZF gearbox to the engine and house the
torque converter.
The complete drivetrain is assembled by
fitting the flywheel, boss and flexplate to
the engine, bolting the bellhousing to the
gearbox and fitting the torque converter in
the bellhousing, then offering the
transmission to the engine.
It’s a seamless arrangement that looks,
from under the vehicle, like standard build.
Compushift
The Compushift is the input
point for bespoke gearbox
settings, allowing it to be
customised to the driver’s needs
This shot inside the auto box shows
typical clutch pack of alternating
friction and steel plates, which are
clamped together when shifting gear
This shows a clutch assembled in its
drum. Clutch packs are operated by
hydraulic pressure generated by the
pump and then applied by valves
rather, remapped by tuning specialist
Superchips to best suit the gearbox
electronics. That mod just happens to include
another 99Nm torque and 38bhp over the
standard (already high-performing) diesel.
Most of us know the ZF4HP22EH
gearbox, even if that name hardly trips off
the tongue: it’s the standard auto unit from
the Discovery 2. This unit is well proven
and fairly bombproof, certainly capable of
distributing a lot more load. But it’s the
Compushift-derived electronic control that
sets Ashcroft’s system apart. Before we get
our heads around that, it’s worth recapping
briefly on how an auto box works.
Automatic transmission
The engine drives a torque converter, which
drives the gearbox. Turbine blades and
impellers in the fluid-filled torque converter
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Dave Ashcroft displays the friction
and steel discs of a clutch pack taken
from a Tdi – typically burnt out by
either wear and tear or excess heat
amplify engine torque at low engine speeds
until the engine develops more power. The
converter then ‘locks up’ and acts as a fluid
flywheel transmitting the drive directly (and
more efficiently) from engine to gearbox.
For rapid acceleration, a ‘kickdown’, which
is operated by fuller movement of the
accelerator pedal, quickly selects a lower gear.
Gears are selected and deselected by
multi-plate friction clutches clamped
together by hydraulic pressure during
gearchanges. The torque converter is locked
up and released by a similar clutch pack.
Failure to achieve torque converter lock-up
speed for prolonged periods, such as when
towing or climbing, can cause overheating
that, in turn, can cause clutches to burn out.
Ashcroft’s system avoids these issues by
programming the gearbox to suit the loads
and driving conditions.
This is the automatic gearbox’s oil
pump, which pressurises the fluid in
the gearbox to operate the gearchange
clutches hydraulically
hardware development
Unlike Ashcroft’s earlier Td5 auto
conversion, the new Ford engine had never
been mated to a suitable automatic gearbox.
To develop a prototype, Ashcroft bought a
Ford engine and cut it in half to install it on
measuring equipment. You’ll see this halfengine in our mock-up pictures. Ashcroft’s
conversions are designed to retain as much
of the vehicle’s factory specification as
possible. That meant the new auto box must
be developed as a ‘drop-in’ unit: a direct
replacement for the manual box. This
ensures the rest of the vehicle remains
unaffected, including the transfer box
position, which, on the latest Defender, is
angled over an additional 10º.
A boss was designed to fit the 2.4 crank
and carry a flexplate that holds the new
torque converter. The flexplate compensates
The Compushift electronic control is the
brain in charge of the ZF auto box. It’s also
the input point for those bespoke gearbox
settings, allowing the transmission to be
customised to the driver’s needs.
Compushift has three menu levels, so
there’s no need to be a genius to adjust the
settings. Simply select the level that’s
comfortable for your own understanding,
or ask Ashcroft to programme it for you.
The Compushift system has long been
around in the US, handling brutal torque
from drag racers and muscle cars.
Ashcroft worked with its manufacturer,
HGM in California, to adapt the logic to the
Defender. Maddison 4x4 in North Yorkshire
(www.maddison4x4.com) had already
worked with HGM on its own Td5 auto
conversion, and assisted Ashcroft in
submitting the ZF auto-box data for a new
system to be developed.
The Compushift system has four basic
settings, each easily selected by the driver:
1. Automatic – conventional auto with
normal facility to hold individual gears,
subject to safety override;
2. Auto with switch shift – fully automatic
plus the option of using a rocker switch for
manual up/down gearchanges;
3. Auto with towing mode – an additional
switch raises gearchange pressure and
speeds to values preset by the driver, so the
box delays the upchanges, spending longer
in lower gears. The torque converter stays
locked up until the driver shifts down to
third, improving downhill engine braking;
4. Manual –overrides the ECU for
competition use where full driver control is
needed. The system is not overridden to
prevent over-revving the engine, so the
driver must change gear at the necessary
times, as with a standard manual.
If the vehicle is towing hard at 50mph
and lock-up speed is 55mph (which is the
Range Rover Classic’s speed), the oil will
eventually overheat.
Conventional automatics have a fixed
lock-up speed that can be changed only by
modifying the hardware inside the unit, but
Ashcroft’s system can be programmed to
lock up at, say, 48mph – giving efficient,
economical towing with no risk of
overheating the fluid. It’s programmable
to any reasonable cruising speed.
Ashcroft designed this
bespoke torque converter
housing (bellhousing) to
mate the ZF gearbox to
the 2.4-litre engine
Housing bolts directly to
auto’s existing mounting
holes. Square cover gives
access to bolt the torque
converter to the engine
Torque converter fitted
inside housing, engaging
its output shafts with
the gearbox input and
oil pump drives
Torque converter is well
inside housing, leaving
room for the new
engine adapter boss
and flexplate
That’s the auto box, new bellhousing and torque
converter assembled – now for the engine fittings
In this mockup (using the
2.4 halfengine), a new
adapter boss
is bolted to
the engine’s
flywheel and
crankshaft…
…followed by a flexplate bolted
on to the crankshaft boss and
driven by it. The flexplate
compensates for run-out
Automatic transmission is then
fitted and bolted to engine. Torque
converter is bolted to flexplate
via bellhousing access hole
Compushift display
and controller
The in-cab display/control unit allows the
driver to customise the gearchange points in
respect to accelerator position, the firmness
and speed of gearchanges and the torque
converter lock-up speed.
Rudimentary shift speed adjustments can
also be made using screws on the side of the
electronic control unit (ECU).
When installed in the vehicle, the
automatic gearbox and torque
converter housing blend into the
typical Defender underside
The display gives a live read-out of the
gearbox conditions. Tab through the menus
to see the following:
l Selected gear;
l Gearbox mode –auto, auto/switch-shift,
auto/towing mode, manual;
l Gearbox oil temperature;
l Shift speed adjust – raises or lowers gearchange points (the road speeds at which the
gears change) as a group or individually;
Dave Ashcroft explains
his choice of torque
converter for the new
system. Auto gearbox
with converter housing
stands behind
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I’m a fan of autos for off-roading and would
have liked to plunge Ashcroft’s only auto
demonstrator into some serious mud. But
with no support vehicle, no winch and no
one else around, Dave was understandably
keen that I didn’t sink his investment.
Anyone who’s been here will know that the
surface consists of clay mixed with Evo-Stik,
which instantly transformed the road tyres
into larger-diameter slicks.
The traction control should deal with that
– and it did. Steep, rutted climbs and
descents on mud that has the adhesion of
cooking fat made no difference to the 90 as
its wheels locked and released under traction
control, with the auto transmission taking
the whole deal quietly in its stride.
The transmission worked well in full auto,
manual hold and switch-shift modes, with
both high and low range on the transfer box.
Engine braking was good in switch-shift
bottom gear low-range although, when
releasing the throttle, there’s a momentary
l Pressure adjust – raises or lowers the
hydraulic pressure activating the clutch
packs. Raising the pressure causes the
clutches to clamp harder, giving a faster
gearchange – useful for heavy towing to
avoid slipping or burning the clutches.
Lowering the pressure gives a smoother,
slower change;
l Hydraulic pressure can also be raised for
low-range and reverse gears to give accurate
driving control;
l TCC – Torque Converter Clutch can be
set to lock-up and unlock at desired road
speeds. To increase longevity and prevent
damage, the TCC will not lock-up above
65 per cent throttle;
l Downshift offset –adjusts kickdown
sensitivity. The higher the offset, the more
readily the box changes down when the
accelerator is pressed;
l Diagnostics mode – for electronically
displayed troubleshooting.
Engine upgrade
Standard ECU maps have an anti-stall
function that depends on sensing a steady,
solid drive from engine to transmission via
the manual’s conventional clutch. So the
Defender’s ECU needed modification to
accept the varying torque transmitted from
the auto box’s torque convertor. This, plus
the engine performance upgrade, took three
months of development.
Inside the cab
The auto gearlever is mounted in a new
injection-moulded console that matches the
colour and texture of the existing trim.
The auto lever is nicely positioned where
your hand naturally drops on to it from the
steering wheel, though it slightly restricts
access to the hi/lo and diff lock lever until
you’re used to it.
Compushift from top clockwise:
wiring for petrol/diesel engines,
essential bling stickers, display/
programmer, ECU, instructions
The ‘CommandShift’ in luxury Land
Rovers, which allows gearchanging by a
simple push forward or back on the
gearlever, is replicated here by a rocker
switch mounted flat on the console – rock
forward to change up, back to change down.
Ashcroft has designed useful extras into
the robust console. There’s a mobile phone
recess with grip mat, and a top recess for
oddments. The rear incorporates a sturdy
cubby box with a lockable lid that folds back
flat to form twin cup holders.
On the road
An automatic should come into its own in
town driving. Leaving Ashcroft’s works to
hack through the Luton traffic provided the
ideal test, and it took little time to get used
The stand-alone Compushift electronic
control unit (housed under the console)
computes driver input to control the
automatic gearbox selection parameters
The ECU sends out its control signals
via this pin-pack on the gearbox to the
electro-hydraulic valves operating
gearchange and torque converter
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Mock-up: half-engine, with boss,
flexplate, torque converter and the
torque converter housing/auto box
(flywheel excluded for clarity)
Oil temperature sensor in
auto box oil sump tells ECU
to vary gearshift pressures
with the viscosity of oil
ECU gets signals from
gear position switch, and
from accelerator pedal
throttle position sensor
All parameters can be adjusted and
monitored by this Compushift
controller and display unit, which
can be mounted in the cab
to this auto box. In traffic queues the auto’s
creep speed is gentle and controllable, and
drive engagement is imperceptible.
Take-off, as traffic moves away, is smooth,
progressive and rapid. There’s the usual
revviness when working on and off the
throttle as the torque converter spins up
and down, but its not intrusive, and gives a
useful, audible indication of exactly what’s
going on down below – in a modern Range
Rover you’d hardly hear this and hardly care
anyway but, in a working Defender, you
need to know what the driveline is doing.
Brush away the town traffic and the
Defender settles out on the open road with
the torque converter locked up into relative
silence after 55mph. It was only after the
Defender stopped changing gear that I
realised I hadn’t even felt the gearchanges –
it really is that smooth.
To my mind, that puts this system
alongside the best contemporary autos.
On kickdown, there’s a satisfying roar
from the engine and torque converter,
justified by a respectable gallop that has the
Defender overtaking 60mph traffic briskly.
On the way back into Luton there was
time to play with the auto’s switch-shift,
using the rocker switch mounted alongside
the main selector lever. Press forward to
change up, backwards to change down. In
this mode the gearchange is sharper (it’s
adjustable) but still smooth.
As a way of controlling the gears manually
it’s more convenient than using manual
select on the main lever, and handier than
the relatively cumbersome CommandShift
on non-utility Land Rovers. To revert to full
auto, the main selector lever has to be moved
to third gear and back to drive, which feels a
tad clumsy. Ashcroft expects to rectify this
soon with a new-generation ECU.
Off-road test
That wasn’t just an out-and-back trip. We’d
been to the Devil’s Pit off-road centre at
Barton-le-Clay (www.devilspit.co.uk).
Console houses conventional auto gear selector and
rocker switch-shift. Phone recess and grip mat to
right of hi/lo lever, oddments tray at rear of console
Armrest opens up to reveal lockable cubby box
whose lid folds back flat, giving twin cupholders
and sandwich platform – neat, user-friendly touch
delay before the engine revs come down.
That feature has to be factored in when
approaching severe descents.
Otherwise, it’s so controllable and slick
off-road that there’s a tendency to forget it’s
an automatic and simply concentrate on
what the wheels are doing, where they are,
and where you’re driving – and that’s just
how it should be.
No mpg figures are available yet, and our
test run wasn’t long enough to give an
impression. But given the minimal effect the
auto box has on Discovery 2, the relative
economy of the 2.4 engine, and the fact that
a chipped engine doesn’t necessarily need to
be thirsty, running costs could be close to
those of the standard manual version.
If so, it’s the ultimate auto Defender.
Getting
converted
Conversion of the new Defender
2.4 to automatic at Ashcroft’s works
costs £5816 and takes two weeks. Book a
test drive in its 90 XS auto to try it for
yourself. The company expects to offer the
conversion in kit form in the near future.
Ashcroft still converts Td5 models to automatic
– and they are now also available with Compushift.
Contact Ashcroft Transmissions, Units 5 & 6,
Stadium Estate, Cradock Road, Luton LU4 0JF:
www.ashcroft-transmissions.co.uk, 01582 496040.
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