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

When I last visited GTO, many years ago now, they were on their 2nd iteration of design (the first servived perfectly well in a 600 bhp single seater and the 2nd design had also been through prototype testing and was on test in the single seater...

This GTO option is now no longer available

Quaife had a 6 speed sequential transaxle for the Esprit for a period and tested it in their own demonstrator car

 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