Renault UN1 transaxle, everything

I thought that "The One Stop Shop" compiling all information under one roof would be nice to have.
Would you please post technical data, tips, specifications, dimensions, reworks, etc.

I"ll start with some specs for different versions of UN1 specimen:

UN1/xxx

> 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.


An original Esprit Renault UN1-016 is 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-Tork ... 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-ed reverse
... LEFT side shift translator
... 1998, modified cross shaft for DIRECT CABLE shifter, no translator.
... Minor durability improvements w/ Sport 350 intro.
... 400 Nm (295 lb.ft) torque rating

Esprit GT3 ......... UN1-028 ... 1998, for the most part like 027
... With lower third & final drive ratios (1.41 & 4.11 ??)
... With higher 5th gear ratio (.076)(0.76 x 4.11 = 3.1236:1 overall)
... 4.11 CWP ratio not suitable for torque of 910 or V8
... CWP is Renault parts, not as strong as Lotus 3.89 CWP
... 300 Nm (220 lb.ft) torque rating due to a weaker CWP
 
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TRANS OIL FOR UN1 w/QUAIFE ATB LSD QDF5M


The QUAIFE ATB Differential does not require any special lubricants.
When running
QUAIFE gearbox internals and a QUAIFE ATB differential we recommend FuchsTitan SYN5 75W90.
For a
QUAIFE ATB differential, running in a rear axle use a hypoid 90 or 75W90, as above.
For those applications that will accept a GL5 or SAE75W90 gear oil, we recommend and sell Silkolene SYN5 75W90 gear oil. We use Silkolene in all our own
QUAIFE racing transmissions.
In reality, any good quality gear oil is fine.

Thanks
Kevin/Lee Jones
GTO Racing Ltd.
Scarletts Farm
Scarletts Lane
Hare Hatch
Berkshire, RG10 9XE
 
Forget that legend about strength difference between a lotus gear and a renault one, there is absolutely none. A metallurgical test could confirm it, the treatment was the same.

What is true is that throughout the years, the gearboxes went upgraded with modifications to the housing, especially around the differential, better machining of the gear set.....

BUT, what is true, is that for Lotus the gears went upgraded with 3 stress risers (ie cuts on teeth). So, normally, but this is not always true, the gears for lotus can be identifed with the 3 cuts on their teeth.

The un1 is a very strong gearbox with a weak gear as the shaft has been extended without any holding structure, so it breaks.

It has been used in many cars : Renault obviously, Lotus, but also Alpine, Venturi and even a US car (not really a sporting one, as it is a motorhome...) branded Vixen TD, if I remember well. Early versions of the UN1 went also used in the delorean.

As our cars are light, they offer a good resistance especially with an oil cooler and a very good oil quality.

Here in France, they are widely used for racing, rallying etc with new gear set (dog teeth).

If you intend racing, I would recommend you to start with a late un1 + the Quaife upgraded primeshaft which then allows you to get rid of the weak points, offers better 1st and 2nd gear ratio with far quicker shifting and a LSD. Personnally, I added to this a custom cutted 3rd gear set (1.26) to maintain a good linearity to my new gear sequence.

Best regards

Stephane

PS : I even know of one guy running a standard UN1 (with oil cooler) , racing every week end, and the gearbox is still alive....
 
Sorry, I had a too quick readiing. You are right about crownwheel and pinion being different. Also , the difference is not in the material, but in the machining specifications. Thus, this gave an adjustable backlash on Alpine, lotus, venturi and a non adjustable on standard gearboxes. Obviously, the teeth end play is a big factor whenn considering fatigue.

Best regards

Stephane
 
Thank you Stephane. Your information is very valuable.

UN1 gear ratios:
............ .21 Turbo ... Esprit GT3 ... Esprit SE, S4, S4s, V8
........... .UN1-013 ... UN1-028 .. ... UN1-016 026 & 027
1st ...... 3.364 .......... 3.364 ........... 3.364
2nd ..... 2.059 .......... 2.059 ........... 2.059
3rd ...... 1.381....... .... 1.41 ?? ........ 1.381
4th ...... 1.03 ............. 1.037 .......... 1.037
5th ...... 0.8205 ......... 0.76 ............ . 0.8205 ... (V8 = 0.76)
Final ... 3.44 ............ . 4.11 ............ . 3.89

1st, 2nd & 4th gear ratios are the same between the GT3 and Renault 21 Turbo versions, but 3rd, 5th & the final drive ratios are different. The final drive is very different, and that would make a huge difference in all the overall ratios (individual ratio X final drive ratio = overall ratio)

1st Gear ......... Overall
3.364 x 3.44 = 11.5722 21 Turbo
3.364 x 3.89 = 13.0860 Esprit SE, S4, S4s, V8
3.364 x 4.11 = 13.8260 GT3

3th Gear ......... Overall
1.381 x 3.44 = 4.7506 21 Turbo
1.381 x 3.89 = 5.3721 Esprit SE, S4, S4s, V8
1.41 x 4.11 = 5.7951 GT3

5th Gear ........... Overall
0.8205 x 3.44 = 2.8225 21 Turbo
0.7600 x 4.11 = 3.1236 GT3
0.8205 x 3.89 = 3.1917 Esprit SE, S4, S4s, V8

Amongst UN1 trans-axles, Lotus were always the strongest, so I've been told..


Beefing it up: Uprated Renault Gearbox

Holloway upgrade kit: Home

One piece, strengthened primary shaft; no 5th gear overhang
Closer ratio first and second gears; 3.00 to 1 and 1.94 to 1
Fifth gear synchro hub
Fifth gear sleeve and thrust washer
Strengthened front roller bearing
Strengthened rear taper roller bearing

See
http://www.hollowayperformance.com/B...ust%202011.pdf
Hi quality Kit made by EMCO Gears

 

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Howard Jones

Supporter
Has anyone tried these double lip half shaft seals?

Transaxle and Engine Pulley Shaft Seals

Any advice on changing half shaft seals, do I really need the special tool or can I do it with careful technique a nice flat plate wih a hole in the center and piece of tubing to slip over ths output shaft.

Any advice on best (easy) method to remove old seal?
 

Ian Anderson

Lifetime Supporter
Supporter
Howard

A piece of pipe. Well that is what it looks like. A neat fit around the splines turned on a lathe with a machined end will ensure the seal is pushed in square

Certainly worked on mine!

Ian
 
+1 with Ian.

Anyway, place it 1mm forward or backward when changing the seal, this will allow the lip to stand over an immaculate shaft section.
 
I think the complaints about the Renault UN1 gearbox are overblown.
The common problem people encounter is with the second gear synchro which can mostly be attributed to lack of driver skill/attention. The first gear on the Esprit is geared pretty low for good acceleration and as a result the 1-2 change comes up on you really fast. If you are not ahead of the car in terms of depressing the clutch soon enough and fully, you're going to wear out the synchro. Likewise you can't just slam it into second gear and not expect to wear out the synchro. You can be quick but you need to develop a feel for what the synchros are doing and let them do their job. You can feel that based on the resistance you get through the gear lever.
 
The 2nd gear trouble comes from several points:

- The mounting of the fork itself wich allows a spring and then introduce a delay between physically moving the gear lever and having the gears really engaging. This issue can be easily solved (getting rid of the spring or using a specific upgraded fork

- The synchro ring spring has to be slighty upgraded to increase the ring pressure,

- Then for cars with some mileages, a disassembly of the hub is necessary to remove by microabrasion the dirt that reduce its sliding capacity,

-Same has to be made on the ring itself,

- Obviously all this, considering that dog teeth are still ok and not rounded.

Few time ago, I designed an upgraded 1st/2Nd synchro ring using molybdenum rather than the standard brass grooves. We made a batch of 200 and the people are really happy with. Unfortunately, the subcontractor closed and my molds are gone. Anyway, I still have a few reserved for friends, I wil take a shot.

Greetings

UN1-027 are not available here in France. They are rather rare as they come from Lotus cars wich are not very common. Anyway, believe my experience and the experience of all these people using it in their gt40s or rallying/autocrossing with them since ages : the material is the same. Lotus people wants to believe that it is not possible that standard renault items are in their cars as the "value" is not the same, anyway the truth is that material is the same. The plant manufacturing them at that time, except having a contra measure to calculate the backlash were using the same material.

(a very close people to me worked there....)
 
I have a broken uprated Renault box which gave up last year- when I opened the box during the weekend the damage was quite obvious. The crown wheel missed 5 tooths, and the pinion were damaged......it seems like rest of the box is intact.....according to feedback I received from the company that provided me with the box, was that the achilles heel of this uprated box were the crown wheel an pinion, everything else would last......Anyone else who have the same experience ? What is strange is that I have been racing for a long time with a "standard" Lotus(with same engine...) box without LSD for years without any problems....
 
The issue you are describing is common for gearboxes that have been opened and reclosed without the right process to do so. Without the original renault tool to adjust the bearing load and without having controlled (and adjusted even if the manual says it is not to be done for standards assemblies, it can & must be)the crownwheel teeth end play, it drives to this issue.

Every time I saw this, I controlled the points above and EVERYTIME it was wrong.

Beside this, oil cooling is an other keypoint. Without oil cooler, they will break

From my side, I have built a lot of these boxes for really hard driving and at the moment none has broken. Even, one I was sure it would break as the guy is racing every week end its gt40 on various circuits and he couldn't afford an upgraded assembly, so basic components, good assembly and oil cooling and still alive. This is for me still a miracle as it should break.
 
The box in question were fitted with an external pump and oilcooler- I would like to believe that the company that build the box for me have the correct Renault tools available, as this is what they are doing- The name of the company is GTO Engineering in the UK...I tend to believe that the box simply has reached its limit for racing use.......the engine is a fairly standard 347 with around 500hp and approx 600nm....Comments apreciated.....

The issue you are describing is common for gearboxes that have been opened and reclosed without the right process to do so. Without the original renault tool to adjust the bearing load and without having controlled (and adjusted even if the manual says it is not to be done for standards assemblies, it can & must be)the crownwheel teeth end play, it drives to this issue.

Every time I saw this, I controlled the points above and EVERYTIME it was wrong.

Beside this, oil cooling is an other keypoint. Without oil cooler, they will break

From my side, I have built a lot of these boxes for really hard driving and at the moment none has broken. Even, one I was sure it would break as the guy is racing every week end its gt40 on various circuits and he couldn't afford an upgraded assembly, so basic components, good assembly and oil cooling and still alive. This is for me still a miracle as it should break.
 
For sure, GTO has a good knowledge of these boxes. Thus, I would not go with what could be called an "amateur" rebuild.

There are few considerations :

The first one is that there are no more new parts (gears, shafts) available for these boxes, thus a specific build or rebuild is done with used parts wich may have been weakened previously. these can not been seen during the build and then they get out when the material stress is very high.

2nd point is that obviously the material of the housing itself has evolved with time, do you have an early or a late housing? Also, is the housing bolt at the bottom uprated to 12 mm or is it still the 10 mm version ?

3rd point : 60 Mkg and 500 hp doesn't mean a lot just considering these numbers as the resistance to motion and the rotation speed are the factors to add to be in position to calculate id the material resistance went reached or not.

4th point : The positive point is that you can easily find a replacement shaft for approx 300 euros wich is nothing by these days....and verify that the builder did the right settings to the assembly.

I hope it will go all fine for you.

Greetings

Stephane
 
Thank you for valuable comments-The box were pit together using new gears and LSD as well as uprated input shaft....I will do what you suggest, to buy a new set of ring and pinion etc, in order to overhaul the box....I agree with your comments related to horspeower and torque- and ability to transfer all of them thorugh the asphalt and not waste it by e.g wheelspin etc. In fact that was the difference when the box gave up compared to previous races...the tire width were increased by about an inch, and the traction were noticeably better....

I will take a look at the numbers of the box and revert.....

Anyway for the coming season I will fit a bigger engine with substanstially more torque and hp over a wider rpm range- so the gearbox will have to be replaced anyway, and I have just purchased a G96/50 or 88 box which I intend to use in the future....

If anyone are interested in 2 UN1 boxes(One original that were supplied with the car from GTD, and the uprated one mentioned above, newly overhauled and with Ford bellhousing), please let me know.....
 
Hello Andre,

It could be interesting if you could post the settings of your car. I mean, it seems that here you may have reached the limit of this gearbox, thus it is a valuable information for the community.

Weight of car
CX (If it is a gt40, this is not necessary as it is known)
Tyres
Engine and torque you already specified them

Also, I believe it was the 3.44 final as it is (due to its cutting) the weakest?

Best regards

Stephane
 
Hi Bruce, no it doesn't. All primeshafts , whatever the UN1-XX versions were all helical and with the same ratios.

The only straight cut gear is the reverse. Maybe, what you consider to be the first gear is the reverse one, as it is a bit different than the earlier versions : teeth stand over a wider surface on the shaft because ont these UN1-XX versions , reverse gear is synchronized.

Best
 
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