Esprit Gearbox Testing
Lotus carries out exhaustive testing to validate Transmission components. The Transmission includes Clutch, Gearbox & Driveshafts. The following is an outline of the Renault Gearbox Program in the late 1980’s
At this time Lotus needed a replacement for the Citroen C35 unit which was going obsolete. The Citroen had been used since the introduction of the Esprit in 1976. What Lotus needed was a gearbox that replaced the Citroen without any modifications to the chassis (this would allow the new unit to be fitted to old cars if necessary) and provide increased torque capacity for future engine upgrades. The Renault UN1 was identified as one of the few possibilities.
This was a good option for Lotus as it had a separate clutch housing and we could design and produce our own unique unit. (Other units did not offer this possibility). Before the first Development gearboxes were built by Renault we evaluated all the options available and discussed and agreed a validation program. (This program was based on their experience with the Alpine).
Input Shaft Length (2 options)
Gearshift Lever on rear cover (several variations)
Gear Ratios (many options)
Final Drive Ratio (2 possibilities) also special material
Speedo Drive (Mechanical or Electrical)
All the Gear Ratios & Final Drive options were subjected to the necessary calculations to identify the vehicle performance. Final variations were subjected to the Lotus ‘Performance Prediction’ computer program.
Prototype vehicles were prepared (Esprit Turbo HC’s) which would be the development vehicles for the gearbox program. Both Turbo & N/A vehicles were used for the exercise. Initial testing consisted of some high speed running at Nardo, Italy to determine Gearbox oil temperature levels. This included the vehicles running at Maximum Speed with many prototype components being used (Clutch Housing, Clutch Fork, Gearbox Mounts, Rear Hub Carriers, Radius Arms, Outboard Brakes, Exhaust System Etc.)
All the parts had to be designed and produced in prototype form as well as production specification. (e.g. Hub carriers were fabricated steel for prototypes and cast aluminum for production). It was interesting to note that the N/A Vehicle recorded a higher gearbox oil temperature than the Turbo. This is because the N/A Esprit had a gearbox undertray that restricted airflow past the gearbox.
The validation testing consisted mainly of road durability mileage, which was similar to the Renault procedure for the Alpine. This included High Speed (Autobahn), City & Alpine Climbing (Germany & Switzerland). The basic Renault test covers 80,000 Km. The Esprit was approved after 100,000 Km.
During this testing the gearboxs were removed from the vehicles at regular intervals and stripped and inspected by Renault.
It became obvious from the first inspection that Lotus required a special gearbox lubricant (Mobil 630M) to ensure satisfactory durability results. This oil was necessary to protect the Crownwheel & Pinion and also ensure satisfactory synchromesh operation. It could also cope with the high oil temperature experienced in some models.
1,000 Mile Abuse Test
1,000 Mile Track (abuse) test.
This consists of 1,000 miles of rapid acceleration (WOT) through the gears followed by deceleration through the gears locking the rear wheels on the downchanges. This works the clutch & driveshafts hard and at the end the clutch life (cover & friction plate) is over.
Standing Start Test
The car is subjected to 100 performance standing starts. This tests the integrity of the Clutch, Gearbox & Driveshafts.
Most of the above was repeated when any increased performance or any gearbox updates introduced. At the Introduction of the V8 other tests were introduced which included repeated hill starts to abuse the clutch.
Over the years the Gearbox has progressed from the original UN1 – 016 with a Torque limit of 300 Nm. to the latest V8 version – UN1 – 027 at 400Nm. To achieve this Renault has made many improvements to the Gearbox such as new Casings, Revised Shafts & Bearings and Revised Gears & Special Build conditions..
We have been able to bring in some Lotus particular improvements when Renault were able to accommodate the revisions on their production line. This became easier as the Renault build volumes reduced and they were able to handle variations with less disruption.
These changes included Revised Gearchange & Synchro on Reverse Gear. The introduction of the Esprit GT3 created another variant of the UN1 gearbox. This variant is only approved for the 2 Litre version of the Lotus Turbocharged engine. This version of the UN1 is designated UN1 – 028 and has a different Crownwheel & Pinion that is only suitable for use and validated for the GT3 engine. It is not recommended for use on the 2.2 Litre Engine.
Basic History of UN1 Gearbox
All the UN1 Lotus Gearboxes are very similar. This is the 'simplified' history.
UN1 – 016 – 4 Cylinder G/Box – First variant of Lotus UN1– First used on X180 Introduction in 1988. This 'Box had rear cover with L/H shift lever.
UN1 – 026 – High Torque G/Box – Stronger Casings etc. introduced circa 1993. This 'Box had rear cover with R/H shift lever
UN1 – 027 – V8 Gearbox – Introduced in 1996 on V8 Esprit. This box was basically similar to 4 Cyl High Torque unit with new Clutch
Housing. It carried over the R/H shift lever. It had synchro on Reverse Gear. A higher 5th gear. The shift mechanism was changed to an improved version of the R/H mechanism from VIN W2272 – this requires a different shift master unit and cables.
UN1 – 028 – 4 cylinder G/Box for the Esprit GT3 (2.0 Litre) with a different Axle Ratio and Gear Ratios - this Axle Ratio is not suitable for 2.2 Litre Engine Torque.
In a nutshell the 026 & 027 Gearboxes are very similar except for the Clutch Housing, Synchro on Reverse, 5th Gear Ratio. The clutch Housings & Rear Cover (with shift lever) can be changed over easily. Minor improvements were introduced at the time of Sport 350 to improve durability.
The Lotus versions of the Box were very similar to Renault units at first sight. What people do not realise is that the Lotus versions had some very important differences. The main issue is the crownwheel & pinion. Although the Ratio is identical to some Renault vehicle applications the material is different. The Renault material will not survive the Lotus application (even the earliest non intercooled cars). Running on the approved oil is another critical item.