Esprit Models
Esprit History
For Sale
Other Stuff
Buying & Running
Parts & Specialists
Other Esprit Stuff

Uprated Renault Gearbox
The greatest Esprit weakness is finally tackled at a user friendly price

GTO Racing Ltd do all of the upgrade kits for the Lotus Esprit. They actually do the Derek bell kit (see below) with even more mods (Strengthening), a 6 speed for the same casing and they are the only producers of the Quaife ATB. all of their parts are from us (They are not middle men).

We can give assistance to all the esprit people out there. we currently stock over 150 gearboxes for the Esprit!

Kevin/Lee Jones

GTO Racing Ltd.
Scarletts Farm
Scarletts Lane
Hare Hatch
Berkshire, RG10 9XE


T: +44 (0)1189 401101 • F: +44 (0)1189 401372 • M: +44 (0)7985 609231 • M: +44 (0)7714 209695 • E: info@gtoracing.co.uk

Lotus Esprit World is currently in contact with a company which already has a successful UN1-13 upgrade and who has just finished the design of a prototype (see above photo) uprated Renault UN1-26 gearbox that will fit straight into the Esprit. The UN1-13 box has been tested in other vehicles up to 500 hp and 550 Nm of torque, which is well within the Esprits requirements. The Esprit version should be at least a strong if not more so!

Lotus Esprit World, working with the company developing this box, hope that an exchange service for a complete uprated Renault gearbox will be possible as well as perhaps a parts kit, to uprate current gearboxes.

Obviously there is quite a lot involved in this project, but the ball is rolling and hopefully an uprated gearbox will be available to Esprit owners for the first time at a sensible price.

Photo above shows a comparison of the original 2 piece shaft and the new one piece upgraded shaft. No nasty undercuts or grooves in high stress areas, and a better material


Left: Close up above showing the straight 3:1 ratio cut 1st gear and closer ratio heavy duty 2nd gear.
Right: Close up of the vulnerable 5th gear end of the standard first motion shaft and the new shaft!

The first uprated Lotus gearbox!

The First Gearbox Upgrade update.
The first Esprit upgrade has now been installed and road tested!

There were some teething problems, one requiring a small increase to the clearance on the reverse idler which is a different shape from the UN1-13 the upgrade was developed for. This is resolved and future upgrades will be made with this modification.

The other problem was actually caused by damage to the 5th gears. These appeared to have been undamaged when the shaft broke, but some teeth were deformed slightly. They appeared to mesh correctly but when the gearbox was installed and the engine run, it was clear that there were problems. As the noise varied with the gear selected, the problem had to be related to the output shaft and it was eventually traced to the damaged 5th gears. When replaced with new gears, everything returned to normal . The car has now been tested and returned to the owner for longer term testing.

The gearbox refitted. (photo courtesy of Ramspott & Brandt)

Note the shiny new end cover, necessary because of internal damage caused by the 5th gears flying free! See next photo. This doesn’t look too bad, but the loose 5th gear has machined off whole parts of the inside of the housing!


I have now seen two broken Esprit gearboxes. And they both had similar damage.

Each has needed:-

5th drive gear and needle bearing

5th driven gear

And in one case

5th selector fork.

spot the deliberate mistake!

It is also clear that the gearboxes fail in a highly similar way

Close up

In my opinion, these shafts have broken due to a fatigue failure due to flexing of the shaft where it leaves the roller bearing. The crack starts at the step reduction in diameter exactly where the roller bearing ends, it then proceeds through the oil hole rapidly followed by failure.


In the upgrade, the shaft is larger in diameter, and there is no reduction in diameter of the shaft ( an obvious stress raiser), as well as being made from a superior material.

The upgrade design is being updated to take into account lessons learned from these rebuilds, and then the definitive Esprit version upgrade will be available later this year.

Upgrades Update
November 2005

New Esprit Version of Bell Gearbox upgrade
As a result of feedback from Esprit users, an Esprit specific version of the upgrade has been developed. Stronger than previous upgrades due to material and design improvements and high quality manufacture by Jack Knight Developments, makers of gear kits for more than 50 years!

Close ratio heavy duty 1st and 2nd gears, with strengthened synchro teeth and improved synchro effectiveness (option)

NO gearbox modifications needed

Compatible with existing Esprit clutches or can use Ford 1" spline clutches

Lower cost! £1995 (exchange price)

Road going LSD option (with upgrade) £500

Professional Gearbox rebuild option with 12 month Warranty on rebuilt box. £375 plus parts

Based on the only proven 5 speed UN1 upgrade with a clean record .

Professional Gearbox rebuild option with Warranty on rebuilt box. Based on the only proven 5 speed UN1 upgrade with a clean record. Next batch delivery late January '06

Contact Derek Bell for further details and to reserve your kit!

All prices plus relevant taxes

Upgrades Update
November 2004

There are now two upgraded V8 Esprit gearboxes in use. In each case the upgrade was straightforward, and they are giving good service, the problems were caused by the damage to the gearbox components when the 5th gear failed.
In each case both the 5th gears, the end cover, and some smaller items needed replacing over and above the new items in the upgrade. These three main items add up to more than £1000. In one case a new crownwheel and pinion, and 5th gear selector fork were also necessary, that's another £1000.
Some think the smart move is to wait to upgrade the gearbox until it fails. There is some logic to this, but could well prove a false economy as it more or less doubles the cost of the upgrade to repair a broken box as well. As well as getting the job done at a convenient time rather than when 5th decides to let go! Similarly, a new clutch is needed to use the upgrade which uses the stronger 1" 23 teeth Ford clutch spline, however as this clutch is not a Lotus specific item, it is available from  clutch makers (e.g. AP) at a significantly cheaper price.
As a result of information gained from the upgrades, the design of the main shaft will be improved to give an even stronger resulting gearbox.
The new upgrades will probably be available early in 2005 once the drawings have been changed and the next batch made.
As part of the upgrade, the gearbox casing needs a small machining operation, the intention is to offer a pair of machined casings on an exchange basis where the upgrade is to be carried out by a competent workshop.


Alternatively, the gearbox can be overhauled and blast cleaned, rebuilt with the upgrade and any new small items needed (seals, gaskets etc) for £500. the result will be a gearbox that looks like new, and is functionally stronger with better ratios than a reconditioned box at a some what higher price. there is also the option of changing the final drive ratio from 3.88 to 3.44:1 which with the higher ratio 1st and 2nd  really makes  the lower gears  taller.

UN1 upgrade kit, exchange price                             £2250
UN1 upgrade kit outright price                                  £2750
Machining Esprit Casings                                           £100
Cost of rebuilding Gearbox and fitting upgrade         £500
Supply and fit ATB LSD                                                £750

For further details contact Derek Bell  
Tel    : +44 (0)1594 826631
Fax   : +44 (0)1594 826466
Mob  : +44 (0)7799 888857
Email: derekbell1@bell-performance.co.uk
Web  : www.bell-performance.co.uk
Gearbox Web: www.un1.co.uk

Ordering/Delivery:-  the upgrade are made in  small batches depending on demand.
Contact Derek Bell for the current situation.
Gearbox's can be turned around in less than a month if the upgrade goes straightforwardly as it should with an undamaged box.

© Alan Paterson

See Derek explaining the upgrade in the Quicktime movie (6.9mb).
Click here for info on playing the movie.

for more details contact derekbell1@bell-performance.co.uk

Jack Knight UN1 gearbox upgrades
JK goes into administration (September 2006)
Jack Knight developments who were making UN1 gearbox upgrades for the Esprit, have just gone into administration, eventually leading to liquidation I am told.

This is very frustrating and disappointing as JKD had been making high performance gear kits for British sports cars since the 50's, they seemed a natural choice as maker of the upgrade. I (Derek Bell) had no knowledge of the impending collapse or any control over the situation, in fact I only found out after the event when I visited them on the off chance when in the area.

I have recovered all the gearboxes there that I could find, but will anyone who has submitted a gearbox or money recently to JKD, please contact me by email (derekbell@bell-performance.co.uk) as soon as possible so I can update you.

I am sorry for any problems this has caused, I was only trying to help keep the Esprit on the road as the supply of Lotus UN1's was drying up due to high power breakages, that was what Lotus told me.

Derek Bell

Living with the Gearbox Upgrade: The Story So Far
by William Ives

An update after 4000 miles on my experience with the Esprit since fitting the updated gearbox. So far I've had no problems with the gearbox, and my original concerns that it would be less 'useable/drivable' as an everyday car have proved unfounded.

If fact from a usage point of view, there is very little difference between the car now and before fitting the upgrade. It is possible to hear a slight additional 'whine' from the straight cut 1st gear but only if you try to listen for it. Selecting 1st gear is no problem at all, and reverse is perhaps a little harder to select but once the technique is mastered its as easy as the standard gearbox.

There is no difference in appearance part from the fact that Derek cleaned and painted the casing so that it appears 'better than new'. In fact this point should be highlighted, after Derek had rebuilt the box it was hard to imagine that it was the same box. The ratios are slightly different in 1st and 2nd gear now being closer together, which I find better than the originals.

When the gearbox was removed from the car, we found we unfortunately had to replace the flywheel as well. The clutch had to be replaced as part of the upgrade, the new gearbox input shaft has the larger ford standard 1" spline in place of the lotus standard 24mm renault spline. Aside from the obviously technical advantage, this provides a very significant cost advantage. The new clutch can be purchased direct from AP racing, AP assembled a special clutch with the 1" spline but with the standard lotus specification otherwise for only £500 plus VAT (part number : CP5082-18GRY(special)) This was about half the cost of the standard lotus item which can only be bought thought lotus dealers.

The installation was relatively straightforward (the only significantly difficulty was the removal of the old clutch due to the distortion in my old flywheel) All in all, a very sucessful replacement, which also came with loads of support from Derek Bell.

Once final point has been the quality of the gearchange, this appears to be inproved and very precise. I did also change the standard lotus ball joints (at the gearbox end) on the selector cable for proper 'rod ends' supplied by PNM Engineering for £19.95 each (x2), part number : PNMF9788 which I would also recommend.

Note: This Gearbox upgrade was not used on the Fifth Gear 200mph Esprit. Although Derek was contacted in regard to the project, his kit wasn't fitted into the V8 Esprit used for their TV show.

Please note that the original Bell Performance UN1 upgrade is

not in production anywhere.

Other "suppliers" cannot be vouched for, some very poor upgrades are in circulation as well as what may be some well engineered ones. The information on this page is just for reference only.

November 2008


If you have an interest in this project email: admin@lotusespritworld.com

return to top
home email news esprit models road tests buying an esprit running an esprit esprit owners maintenance pictures for sale history Lotus models links