PhillipM

If it looks like this it's a '5:

The slight efficiency increase is as much from reducing the lateral thrust loads than the actual torque transfer efficiency itself, but yes, helical gears are actually stronger for a given size/material.

I asked Opie about Millers CRX 75w-90 NT as a replacement and they agreed it should be fine, I'm just waiting to hear back from Millers themselves but the specs look right.

^I'm still trying to find a plate-style diff for that though if anyone has any ideas....

Hey all, newbie here, but I have to agree with the above, there's no real strength issues with anything bar 5th - and that's down to the design of the shaft and the gear being hung outside the casing, rather than an issue with the gearpair itself. As mentioned, the differential's don't take kindly to one wheel spinning for too long - in fact the only time I've damaged a diff* so far is when it was spinning one wheel a lot faster than the other for a good 30 seconds of full throttle - I think the oil overheats given the spur gears just run on a backing pad, and then you get galling and a tooth lets go. The preload on the crown and pinion is vital too. Input shafts can be a little weak but tend to just wear the splines rather than outright snap unless you have silly amounts of load. Syncro's are relatively old design and fairly fragile - if you baby them until the oil is warm, they are fine. The other option is use an oil such as Total BV75w-80 which massively improves things but possibly at the expense of wear on the hypoid diff gears - although it hasn't been an issue for us so far. The box will quite happily take 10,000rpm's of input speed from what I've found, but the nose bearing on the input shaft is worth replacing beforehand! *Albiet using the UN5 diff with it's 4-spider internals rather than the 2 spider.