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benjamincalleja

Question about UN1 strength vs engine

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No you get just the ATB diff... you will need to swap over the CW. The pinion is part of the secondary shaft.

Just a note, fitting an ATB or slip diff will increase the loads within the box, because you will have doubled the

traction grip from the wheels..

As i said before it is rare for a 4 pot to destroy a box, unless blatantly abused.. I put 370 ft lbs through mine with

quite a bit of abuse for 6k miles, it was only when i went up to 409 ft lbs that 5th let go.. The rest of the box seems

to be able to take a lot ..

And the CWP can shatter if you do snap changes while spinning the wheels, or aggressive burn outs.

The weakest point on the GTO competition  box is the CWP , but it take some doing to brake it on a road car..  

That's interesting considering the amount of V8 owners with (supposedly unmodded) vehicles losing 5th... 

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> The initial Lotus unit - UN1-016 had a Torque Limit set at 315 Nm (232 lb.ft).

This Version used different Crown Wheel & Pinion Material compared to most other Renault Applications (except Alpine, which had a different direction of rotation). Differential also had 4 Pinions like the Alpine & some of the Agriculture Units
 (UN1-023 and UN1-024).The Lotus Version also had extra Dowels in the bell housing Joint to further control bending.

 

>The UN1-026 (known as the High Torque Box) had new Casings which were stronger to reduce Bending under the increased Torque. The Main Fixing Bolt Size & Torque was also increased. There were some revised bearings and retaining plates introduced at that time. The Torque Limit was increased to 400 Nm (295 lb.ft)

> When the V8 came along (UN1-027),  it carried over all the 026 features. Plus, there were also updates to the shaft machining & gear assembly procedures as well as well as the revised 5th gear ratio, synchro was added on reverse.
> For the GT3 (UN1-028) we changed 3rd gear the Final Drive Ratio to suit the Engine Performance. This revised Final Drive Ratio came with a lower Renault torque limit of 300 Nm (220 lb.ft).

 

 The Gearboxes had to use a specific lubricant to eliminate Severe Crown Wheel & Pinion wear (Mobil SHC-630M... no longer produced, or Castrol TAF-X... also recently discontinued by Castrol).This was introduced during the initial development testing. The standard Renault lubricant (Elf Trans elf TRX) did not give enough protection due to the Load and Heat produced by the rapid Esprit Turbo Engine Torque rise.

> At all times the gear ratios used in the Lotus application were standard Renault, but the Lotus Crown Wheel and Pinion used upgraded materials. The Renault CWP parts will fit, but they're not as strong.

 The main problem was in the stiffness of the Transmission Casing and the loading on the Crown Wheel & Pinion. The Lotus versions of the Renault UN1 Transaxles are the strongest variants available. The only thing that comes close is the later Renault Alpine GTA UN1-019, but it has a different direction of rotation and different final drive Ratio.
> The UN1-013 from the Renault 21 Turbo would provide some of the gears (not 3rd, 5th or final drive) and synchros suitable for the GT3.

 *****
Yours is the original Esprit Renault UN1-016... standard in the non-SE and the SE.
The high-torque box started in 1993... 1993.5 SE and the S4 in Oct 93.
Just by looking, the shift translator is on the left side, and there should be an ID tag, or stamping, on the gearbox
.
*~*~*
Esprit Original .... UN1-016 ... Started with first Renault equipped Esprits
... 1988
DOM / ROW intro
... 1989 Federal intro, non-ChargeCooled, and SE.
... With 0.8205 5th gear ratio (0.8205 x 3.89 final = 3.1917:1 overall). Left side shift translator, 315 Nm (232 lb.ft) torque rating
Esprit Hi-Torqe . UN1-026 ... 1993 intro (1993.5 SE and the S4 in Oct 93)
... Stronger case with new castings
... RIGHT side shift translator
... 400 Nm (295 lb.ft) torque rating

Esprit V8 ..... UN1-027 ... 1996 intro, for the most part carried over 026 features
... V8 bell housing - does not share 4-cyl bolt pattern
... Higher 5th ratio (0.76)(0.76 x 3.89 = 2.9564:1 overall)
... Synchro reverse

A082F4150F,right side translator UNI 027 - V8, prior to '98 MY http://www.deroure.com/applications.asp?MAK=1&ST=A082F4150F

... 1998+, modified cross shaft for DIRECT CABLE shifter, no translator.
... Minor durability improvements w/ Sport 350 intro.
... 400 Nm (295 lb.ft) torque rating, LEFT side shift translator

 

 

UN1 – 028 – 4 cylinder G/Box for the Esprit GT3 (2.0 Litre) w/different Axle &Gear Ratios - 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 realize is that the Lotus versions had some very important differences. The main issue is the crown wheel & 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.

 

Italy was one of the principal markets for the GT3, and Romano Artiolli's company (Lotus' Italian Distributor) was one of the motivators behind getting the GT3 built.
             

Edited by MrDangerUS

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That's interesting considering the amount of V8 owners with (supposedly unmodded) vehicles losing 5th... 

 

I think all depends on how they drive them,  Powering along in 5th then backing off then reapplying power

will flex the overhung gear stressing the shaft..  Its only a matter of time before it goes in that case..

Because of those extra torques the V8 has , it is easy to cruise in 5th and power away, in the four pots

you would tend to drop a gear..

At 370 lb ft (500 Nm)  I was 20% over the manufactures spec and a tad more than the std V8's . I knew this

was pushing the limits even accounting for the allowance manufactures build in..  How much damage got

done in the 6k miles with flexing can only be surmised.  When pushed to 409 lb ft (554 Nm )  the inevitable

failure occurred... 

What should be noted was I using the tall 5th with power a lot , not just for cruising.. If i had used 4th for the

power surges,  and lets be honest here , that give a 148 mph capability, and 5th for cruising then it may of 

lasted longer..  We have not seen regular catastrophic failures on any other gears even with modified engines.  

 So driving style may have a lot to do with failures and the reason why some and not others last the time they do.!

My suggestion to those who have concerns is to use 5th for cruising and 4th for full power..

 

For reference, I was using a 2001,  UN1 027. with direct cable shifter..  and TAF X oil ..

   With the later installed GTO set up I also used  TAF X , However after recent service rebuild I installed  Millers

Nano tech oil as a replacement.. During testing with this oil we noted a 3% reduction in loses..

( Tests are ongoing at 450 lb ft - 610 Nm )

 

Hope that help throw any light on your query.  

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If the UN1-016 used in the (early) SE can only handle 315Nm, how come we don't hear of more problems, with the engine producing 354Nm?

Not questioning the info above, just wondering because the difference is quite large.

 

Filip

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I think all depends on how they drive them,  Powering along in 5th then backing off then reapplying power

will flex the overhung gear stressing the shaft..  Its only a matter of time before it goes in that case..

Because of those extra torques the V8 has , it is easy to cruise in 5th and power away, in the four pots

you would tend to drop a gear..

At 370 lb ft (500 Nm)  I was 20% over the manufactures spec and a tad more than the std V8's . I knew this

was pushing the limits even accounting for the allowance manufactures build in..  How much damage got

done in the 6k miles with flexing can only be surmised.  When pushed to 409 lb ft (554 Nm )  the inevitable

failure occurred... 

What should be noted was I using the tall 5th with power a lot , not just for cruising.. If i had used 4th for the

power surges,  and lets be honest here , that give a 148 mph capability, and 5th for cruising then it may of 

lasted longer..  We have not seen regular catastrophic failures on any other gears even with modified engines.  

 So driving style may have a lot to do with failures and the reason why some and not others last the time they do.!

My suggestion to those who have concerns is to use 5th for cruising and 4th for full power..

 

For reference, I was using a 2001,  UN1 027. with direct cable shifter..  and TAF X oil ..

   With the later installed GTO set up I also used  TAF X , However after recent service rebuild I installed  Millers

Nano tech oil as a replacement.. During testing with this oil we noted a 3% reduction in loses..

( Tests are ongoing at 450 lb ft - 610 Nm )

 

Hope that help throw any light on your query.  

Thanks for the insights. Thing is, of all the failures I've heard of, it was people cruising in 5th that it happened. I generally don't touch 5th in the V8 as a result.... 

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If the UN1-016 used in the (early) SE can only handle 315Nm, how come we don't hear of more problems, with the engine producing 354Nm?

Not questioning the info above, just wondering because the difference is quite large.

 

Filip

 

Most manufactures will build in a safety margin and the difference in this case is less than 15% over, As a result

it probably falls within these margins which is why we don't see the failures...

Also as I previously said, on the four pots we tend to use 4th as the angry gear..

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I agree about the margins, but that should also apply to the later box. Yet the V8 that (on paper) doesn't need to rely on the margin does seem to be hard on 5th? I couldn't imagine not using 5th on my SE and am planning to change the ratio to the taller V8 one, as I did on my previous one. I do have a gentle driving style though.

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I believe the 'box was revised twice - first for the S4s then again for the V8. No clue about v8 margins. But I have a feeling that it probably has none...

Gentle or not 5th seems a bit hit and miss on the v8, although people losing 5th while cruising might have lucked out - previous owners could have abused 5th at some point weakening it in the process..

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Just curious - my car's data plate says it was built NOV 92. It was registered as a 93 SE by the first owner. What do I really have in hand? a 92, 93 or 93.5 as far as this topic goes and which UN1 tranny? I am thoroughly confounded now. lol.

 

And the final question: I have supposedly installed a Lotus Motorsports  (JAE sourced) - paid to have it done and provided it to Jamie Goffaux) but not truly sure I even have my original transmission internals in the case as he gave me back one that looked completely different than the one he showed me as mine and in a completed state while in his shop months before I got a totally differently looking one back when removing my bits from his shop to another that actually started working on the car after 18 months in his shop. VIN's match but that is just the casing... I am still at risk correct? lol.

Edited by MikieP

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You have a 93 SE.  There were no '92 SE's in the USA, they took that year off;)

 

The 93.5SE  had the later body colored door handles, a taller wing, and the later interior similar to the S4.

If you raise the wheels off the ground, and turn one wheel, you'll be able to tell if you have the limited slip differential, though you should be able to feel while driving as well.

 

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Thanks, Travis! How would I know I have one by driving one. I am completely in the dark as to how it should feel. Also, someone told me the reaction of the rear wheels when rotating them for the Lotus LSD was not the same as was for the other types of LSD's out there? Would have replied earlier but did not know you had placed comment as still no email notifications from TLF on followed threads.

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If it's got a Quaife then the LSD test won't work. Do a hard start with one wheel in the gravel and the other on the tar. With a Quaife you should get good hook up and not an excessive spinning wheel in the dirt than an open diff will give you.

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The Quaife and Lotus ATB (automatic torque biasing differential) are very similar to a Torsen type LSD.

Quaife

1bb58694db9a6f659820305f842ed27f.jpg

 

Lotus ATB

 

lotus%252520sport%252520300%252520lsd.JP

 

 

 

 

 

Edited by Vulcan Grey

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By the way, just tried it with my Quaife.  With the car up in the air, and the transmission in neutral, if you spin one rear wheel, the other wheel does not spin.  That is with the hand brake slightly dragging.

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By the way, just tried it with my Quaife.  With the car up in the air, and the transmission in neutral, if you spin one rear wheel, the other wheel does not spin.  That is with the hand brake slightly dragging.

That would be because there is no input torque to the crown wheel. Without torque, there will be no (or insufficient) forces on the planet gears to make the differential lock. We saw the same thing when playing with torsen diffs in Land Rovers, you always need input torque and a minimum of resistance to one wheel to make them work. TorSen stands for torque sensing, as opposed to speed sensing LSD, that use friction plates to keep the speed difference between both wheels limited.

I wonder if you'd put the transmission in gear and then try to rotate a wheel, it would be enough to make the diff lock instead of having the other wheel rotate in the other direction as in an open differential.

Filip

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Pretty sure I have the second one shown. If you pick it up wrong way round things fell apart. And after reading all above, I am getting the impression I will have better traction and I am more at risk of chunking things up when going up the torque scale then?

Edited by MikieP

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On 12/9/2015, 12:23:00, CHANGES said:

keep in mind too these will be quoted as the highest acceptable torque on the weakest link.  ie, the weakest gear can take 315nm, the others can probably take alot more.  so perhaps the SE simply reduced boost (and thus torque) on the 5th gear (im presuming that was the weak one) down to around 315nm and kept the 354nm on the others where appropriate.   that would mean though that the "analogue" turbos could be prone to breakage without that feature?  guessing here.  funny though, you never really hear of the pre SE turbos having gearbox trouble, probably because of the lower engine power/torque in general?

 

Most manufactures will build in a safety margin and the difference in this case is less than 15% over, As a result

it probably falls within these margins which is why we don't see the failures...

Also as I previously said, on the four pots we tend to use 4th as the angry gear..

 

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1st and 2nd gears ratio is tough on the synchro rings, (are too tall).

This says it all:

Bell_renault_un1_info_02.pdf

Bell_renault_un1_info_04.pdf

Edited by MrDangerUS

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John,

You do realise you are posting in a thread that is 3 years old without any posts other than yours since January 2016?

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Just going to add my experience for those with a GT3. Everything I'd read said that the GT3 has the weak box until I saw one post that said they started with the 026, switching to the 028 in mid '98. I had a look at mine last night and the tag on the box shows it's an 026, so one of two things must have happened:

1: The box has been replaced at some point, either with an 026 or something labelled as one.
2: The GT3 started out with the 026 and switched later

Best to always positively identify what you have, as I was fully expecting to have to buy a new gearbox based on what I'd read.

I'm still going to try and identify it through the ratios as well, rather than just trusting the tag. I also have to thank Dave (Changes) for all the advice he's been giving me on Esprit transmissions.

Edited by cammmy
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