Originally Posted by
rick130
Ashcroft's are covering their butts with that recommendation as most EP90 fluids available in the UK are just basic diff fluids and so will work ok.
First and foremost the ideal fluid wont contain LSD additives.
Any LSD friction modifiers will result in little to no torque biasing, you'll pretty much render the diff useless.
I also believe you need a multigrade as the lube holes aren't that big.
A few people have destroyed LT230 ATB's in race situations that appeared to be from a lack of lube.
A multigrade will flow much more easily into the gear pockets until the diff reaches operating temps. And Rover diffs run pretty cool anyway, they don't generate much heat.
The best fluids for a torque biasing diff IMO are transaxle fluids, eg, designed and formulated for manual transmissions.
They contain the correct friction modifiers for synchros, which also work well in helping the helical gears bias.
I've always plumped for Motul Gear 300 75w-90 (not the lsd version), and interestingly that's what Wavetrack recommend for their torque biasing diff.
Quaiffe recommend Fuchs Titan Syn 5 75w-90
Both are full synthetic fluids, with no LSD additives and have the correct friction modifiers for synchros.
Castrol Syntrax Universal, etc. would be good choices, too.
Oils like Penrite Pro Gear 75w-90 don't play well with ATB's, even though they're touted for manual transmissions as they contain LSD additives.