GEARBOX/CLUTCH
The Renault/Maserati UN1 transaxle, used in the
Esprit since 1988, when it replaced the Citroen transaxle
of the Turbo Epsrit, has for long been the weak
point in the drivetrain
An
alternative transmission has been sought for the Project M71
Esprit for some years but a final decision has not yet been
made...
The gearbox visible
on the back of the V8 engine is actually just an empty
UN1 casing, with selector rods and a reverse gear
The UN1 has several weak points - the main one
being the two piece input shaft, comprised of the Clutch Shaft
and Primary Shaft (items 27 and 12 in the diagram below), which
steps down to a smaller diameter, introducing weakness but also
the overhanging 5th gear in the rear casing, which was added to
the original design and probably some undersized bearings
There have been several
upgrades, from a number of companies, to address these
weaknesses - GTO
Racing have this popular one piece input shaft with
close ratios 1st and 2nd gears and the UN1-027 had a larger
52mm rear shaft bearing
Similar upgrades were also developed by Jack
Knight and Bell Performance but neither are now trading
Click on the right for a descrition of an
upgrade kit for the UN1 used with a Chevrolet small block engine
GTO Engineering were also
developing a full kit with 6 speed
gear-set/shafts and up-rated bearings to replace
the UN1 internals, in the original casing
This is a close ratio 6-speed dog engagement (as opposed
to synchromesh), straight cut gear (stronger but noisier than
helical gears), gear and shaft set for the UN1
It still has a 2 piece input shaft but could reportedly handle twice the torque of the standard unit
A few Esprit owners fitted theses units but reviews were
mixed - Lotus
actually worked with Quaife to develop a 6 speed sequential
gearbox for the V8 but ultimately cancelled the project for
cost reasons
This Quaife
option is now no longer available
X-shift have a Universal Sequential
Gearbox 5/6 speed dog engagement transaxle, which can handle
torque levels of 900-1000 Nm
It reportedly has a bolt pattern that aligns with the standard UN1
Esprit bell housing and it has been campaigned in hill climbing
The clutch for the Project M71 Esprit will not be selected until the gearbox
The standard Esprit V8 clutch is shown on the right
- the V8 was fitted with a 215mm dia twin plate clutch, after a
short run of production with a 280mm single plate version
The hydraulically operated pull-actuated mechanism
permits a higher clamping load for the same pedal effort
JAE have a twin-plate Esprit V8 clutch upagrade with
one sprung/one solid hub,
It supports the pull type diaphragm spring, with an
aluminum basket and uses an advanced friction compound