Another UN1 Crown/Pinion failure - doh!!

Hi all -

Got to the bottom of Roys transmission failure today.... The crown wheel/pinion has let go. Counted some 10 teeth missing + punched a 30mm hole through the differential housing casing.

Anyway - spare box stripped for bits and all should be together again for Brighton Speed Trials on Sept 10th.


Did it have lSD? Have you considered using oil cooler? what are the tranny's oil temps during event? My experience suggests that when things go over 130C it is a "safe" way to disaster.

I remember when my first final drive let go - first minute I was starring at the windows - I expected to see some kind of helicopter or something chasing me! Than I realized that it was my car making all that noise...

Thank You
Hi Ted
yep - it had a Quaife ATB fitted + external oil cooler + pump.. No Temp guage though but it will get one now!

One thing we wondered is we currently use a solid centred 6-paddle AP clutch. (i.e. NO dampening springs at all)

IT is a bit fierce, but the sprung centre type exploded last year and this is stronger. What we wonder though is whether this is likely to shock the crown wheel too much?

Anyone got any experience with these solid centre paddle clutches???
Hi Paul,
I always raced solid center clutch discs. I don't really think that ring/pinion failure is caused by tranny shock loads. It seems that usually this is due to insufficient lubrication -> local temp raise. Insufficient lubrication is normally caused by excessive oil temp - it simply foams and there's no oil film on cogs. If you look at usual curves of steel strength vs temp (I don't have it handy) it's obvious that high temps doesn’t help at all. Also fatigue life is severely reduced.
I usually used Castrol SAFX -J oil. Don't put it in a synchronized box as it will eat sinchros rapidly.
Our problem was (raced BMW320 in RTCC - same tech.reg as WTCC) that they (shitheads at BMW) use same weak and tiny ring and pinion from 316 to 320 models and they failed to homologate usage of say 325 diff. How ever with sufficient cooling (external pump and proper ducting to cooler)we had no more probs.

I would suggest to fit an diff oil temp sensor - this way you'll know exactly what is going on there. Eliminating LSD will reduce diff temps drastically.... it will also make you slow.

Thanks for the insight Ted, for the moment, clutch plate will stay, crown and pinion has been replaced, temperature sensor fitted to differential chamber below fluid level and pump will be used for sure...

We currently use the Quaife reccommended Silkolene Syn Tran synthetic gear oil, but am considering the 'Redline' racing alternative.... Any thoughts...??

Will let you know readings once we have some data - fingers crossed! /ubbthreads/images/graemlins/wink.gif

Oh - and the ATB diff is definately staying - transformed the handling when initially fitted. /ubbthreads/images/graemlins/grin.gif
Thanks Paul, keep us informed.
I have no experience with Redline - we used Castrol because we didn't have to pay for it. But I know teams who used Redline with great success. Also you may want to install an oil filter in the line out of diff to the pump. Goodrich makes some - they fit in their oil lines and fittings. We used to inspect the filter after each race/test day. If ferrous debris was present we would inspect ring and pinion and if it has signs of eccessive heat and dents on the cogs we would replace it. We replaced diff ahd engine oil after each day (aprox. 100km). I believe that oil, when subjected to extreme conditions (9000+ RPM), degrades very rapidly.
What was in the diff before ATB? Would you like to describe cars before/after handling?
What is car usage?


PS: Sorry for my English
Paul, we are useing the new MOTUL 75W90 oil in Martins ZF, I am advised by Techcraft that this oil will take extreme temperatures and is used in most race cars they service. Frank
Hi Ted
Pre ATB, the box had a standard Renault diff. These we know suffer when you wheel-spin a lot. What tends to happen is when wheelspinning, the planet gears within the diff spin extremely fast. They are of plain bearing design and the pins on which each are mounted then get very hot. Once hot, they risk siezing and the pins then break. Once broken, then you either lose drive (not too bad), or the pin (or part of) exits the large hole in the side of the diff and then either locks the rear wheels, or it then gets between the crown and pinion (ouch!!) - I know of 4 other competitors who sufferred this type of failure before changing to Quaife ATB.

Roy and I fitted I believe the first ATB to a UK competetive car (I think) but had not sufferred failure of the Renault type. (Gentle aren't we? /ubbthreads/images/graemlins/grin.gif)

Anyway, the differences have been described before but I will repeat our own observations again.

PRE ATB - the car was more difficult to launch well, especially if wet and the more power Roy provided, the worse it got.

POST ATB - the car can be launched with confidence, we often launched in second gear with the 347 motor and acceleration at Longleat Hill climb was logged at 0-60 3.7s and 0 to 100 at 7.6s. It was also noticed that the car would readily leave two, 12" wide black lines from a standing start if pressed hard. (checkout the 2004 Brighton Speed trials clip on our Website Video Section )

PRE ATB - when driving round circuits it is always difficult to press hard, when cornering, a small amount of body roll + a little too much throttle would lead to the inside wheel spinning. This loss of traction also resulted in both a loss of lateral grip and a reduction of forward drive, which would tend to make the rear end suddenly step out and break-away with possibly fairly dramatic oversteer. Whilst it can be caught if you are quick, it never gave what i would describe a 'positve feel' and having additional power available just made matters worse.

POST ATB - Circuit driving is much fun, the car feels more stable, you can push hard through corners, knowing that if you start to lose traction, it is on both tyres and progressive. i.e. no sudden loss of lateral grip - which in turn leads to an ability to 'drift' the car around some of the faster corners. This was being done to reasonable effect at Lydden circuit when only Roys car was fitted with the ATB. As we double drive, and I ran out of class, the other drivers got a chance to view/video and whilst I was not aware it was happening to any great extent, you could clearly see the car drift first its rear then the front (slightly) through the fast right hande at the bottom of hairy hill (?). It also meant that if the car was understeering slightly, which it tended to do at the tight hairpin at the top of the hill, a bootful of right foot would loosen the rear in a more controlled manner allowing the front to tighten up on the corner. It is a lot more fun now, especially with more powerful engines.

Of the bunch of us in the UK that Sprint and Hillclimb - I think they ALL now have ATBs. I also recently fitted one to Club member Bjorn Arnils GTD40 (Also UN1) and he too is amazed at the difference. Again he has a fairly powerull car (400+BHP) and its road manners, especially when pulling off from junctions, or in the wet, are far less frantic than when the std diff was fitted.

So there you have it - 'A Totally Biased' opinion /ubbthreads/images/graemlins/grin.gif

Once last thing, the unit has been on Roys car now for at least 3 maybe four seasons (or is it five?) and it has been totally reliable. The one time we thought there was a problem, in fact there wasnt....

ps - we have a filter on the g-box and will be checking it after each event.