When I purchased and fitted the Ashcroft Transmission ATBs into my D2 I spoke to Dave Ashcroft about what oil to use and he stated the normal oil as per standard specs. No worries.

As a result of this guidance I've been more recently using Penrite Pro Gear 75W-90 (< PRO GEAR 75W-90 (Full Syn.) | Penrite Oil > which states "Pro Gear 75W-90 is already dosed with the correct amount of friction additive for use in Limited Slip differentials, no extra additive is required, nor should it be added as seal degradation may result.") as it's listed in Penrites lube guide for the D2 and I assumed the few extra dollars for the full synthetic superior fluid would be worth it. For the past few years I just haven't believed my ATBs weren't fully functioning correctly as a sometimes when off road I just didn't have the drive that I expected and had previously had - there's a discussion on here I started about testing them but there wasn't a definitive method.

A side track chat with rick130 is Gear box oil and I learnt from rick about ATB's wanting the opposite of what clutch type LSD's want in their gear oil - in other words if the gear oil has the LSD additives in it then you don't want to run it with your ATBs. Here's rick's words:

Quote Originally Posted by rick130 View Post
Most 75w-90's have LSD friction modifiers added...

LSD friction modifiers increase slip % in a controlled way to reduce LSD clutch chatter.
If you've ever used a non LSD fluid in a clutch pack LSD they chatter and lockup fairly harshly.
The FM's in a manual trans fluid are optimised for manual gearboxes, their friction coefficient increases as rotational speeds approach each other, the opposite of an LSD fluid and for that matter engine oils and Dex II/III ATF's
The ATB relies on the helical gears in the pockets friction increasing to bias torque, whereas an LSD additised fluid will try to minimise that friction.
On the weekend I drained out my two ATB diffs (front and centre) and refilled with the cheaper semi synthetic Penrite Trans Gear 75W-90 < TRANS GEAR 75W-90 (Semi Syn.) | Penrite Oil >. This fluid is not suitable out of the bottle for LSD use - with the website stating:

For Limited Slip Differential applications, a dose of Penrite Limslip Additive is required to be added to the oil.
The difference on the road was noticeable fairly immediately with the front diff functioning again there is now some pull/resistance on the steering wheel when accelerating/powering through corners as the diff tries to self centre/pull straight. This used to be there years ago when the ATBs were definitely functioning correctly.

So big lesson learnt by me about what a large difference a small additive pack such as the LSD additive can make in the fluid, a big thanks to Rick for the oil and additive lesson and I'm posting this up as it might benefit others too in the future...


On a related note I personally default to Penrite for my fluids as they're well priced and easily accessible and stocked at a variety of retailers (Repco, Supercheap Auto, Autobarn, etc.) but I'm sure others are available too.

On the to use list are:
  • Penrite Trans Gear 75W-90
  • Motul Gear 300 - non-LSD version recommended by Rick


On the maybe list are:



On the do not use list are:


  • Penrite Pro Gear 75W-90 as has the LSD additive in it
  • Gulf Western Oil Ultra Clear Gear Oil Low Vis 75W-90 as states "Suitable for limited slip differentials calling for 75W-90 viscosity grade gear oil." on the product page < http://www.gulfwestern.com.au/produc...etic-ls-75w90/ >