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Hello all,

I compete in Classic Trials events. My car is based on a Herald chassis with a 1500 Spitfire engine and gearbox. The differential used is a late (larger crown wheel/pinion) Vitesse assembly. Ratio 4.1:1

I am relativley new to the sport and have competed only a few times with this car. In this short period I have broken one diff assembly during an event. This is not the first time in my cars life that it has suffered from diff failure and I'm sure it wont be the last.

The nature of the sport means that one wheel is often spinning hunting for grip. Limited slip diff units are not allowed within the rules.

Upon inspection of the broken diff assembly (which had privoisly been stripped and the diff pin replaced with a phosphor bronze item) I found the diff pin to have sheared in two places, just in board of one planet gear and just out board of the other plannet gear. Both planet gears had broken into many pieces each. As a consequence of the broken parts the crown wheel and pinion gears were damaged (I was towed a short distance). Thier was evidence of fretting/pick-up on the pin where the planet gears run. I am unsure if the planet gears or the pin failed first. At the instance of failure the clutch had just been let out, their was no wheel spin at all immediatley prior to failure.

I have replaced the diff with another 4.1:1 late Vitesse diff, the diff pin is EN36B hardend to approx 55Rc modified to include a neddle roller bearing between the pin the planet gears. I have filled the diff with Redline heavey weight shock proof gear oil.

The reason for this posting is tap into this vast resource of knowledge and start a thread about how the triumph diff unit(s) can be strengthend for trials car use. Does anyone know of other developments first hand or otherwise? Has anyone heard of a modified diff to include 4 planet gears to spread the load?

All suggestion/comments are welcome.

Thanks for reading.

Regards

Daniel Minett-Smith