N4S - No, I have put plenty of new belts on, but not since I've replaced the diff pulley, so I am hoping when I get my delrin diff pulley and the new belts that my problem will be solved.
Jon - They are freying, not just a straight snap. I've just noticed that the pulley fence is loose on that side of the diff, maybe the edge of the pulley is rubbing on the belt??
Protc3 - That's what I'm thinking it might be also? I may have set the guides slightly crooked maybe and that with the loose fence is rubbing on the belt causing it too weaken??
To everyone - how does your belt look after a race meeting?? As mine looks worn, like a feathering only after a couple of runs? Which may point to it rubbing on something?
Thanks everyone for your ideas, as it really is frustrating, I'm really starting to get the car handling awesome. This is the only thing holding me back with it.
So once I've got my Schumacher order with my parts in it, I'll rebuild it, double checking the guides and fences and I'll let you all know how I go on the weekend.
Iain