If you don't know your diff which oil do you use?

[someonestolecc]

Gday,

I have a mechanical diff of some sort and the oil has never been changed from Japan. I've been told you need to know the grade of oil that goes in.

I have no idea how to find this out other than hoping that there are markings on the diff somewhere that identify it.

Are there really grades of diff oils based on brands or will a certain grade of oil fit any mechanical?

[Busky2k]

Being diff, the first criteria is that the oil must be rated as API GL5. Secondly, being a mechanical diff, the fluid must be friction modified in order for the clutch packs to lock up properly without shudder etc. So the oil must say on the bottle it is suitable for mechanical differential applications. If it doesnt, don't use it. (for stock viscous coupling units, this is NOT an issue) For example, Motul Gear 300, Redline 75w90 NS and Castrol MTX are GL5 oils, but not diff oils. Castrol Syntrax, Redline 75W90 and Motul PA 90 on the other hand re. So take a look around at the performnce shops

[someonestolecc]

Ahh thanks!!

And as long as it's for a mech diff it's all the same so any of those should be ok?

And I should be using Castrol Syntrax, Redline 75W90 and Motul PA 90 for the aftermarket mechanical diff?

Also how many litres do you usually need?

[someonestolecc]

Just called UAS to see how much they sell this for-

redline mt90 - $29/quart

motul PA 90 - $22.99/2litre

Is the redline THAT much better that its more than double the price?

[Busky2k]

Yo man, Redline MT90 is a GL4 gearbox oil, not a diff oil! Hehe but Redline 75W90 Gear oil is the same price.

If I were you, i'd go for the Motul PA 90 or Castrol SAF-XA which is a full synthetic. (Sorry I said Syntrax before, thats not a diff oil, but a gearbox and non LSD diff oil). You can easily find SAF-XA in any auto store or Big W (its in a silver bottle). Alternatively you can use Castrol LSX 90 which is a mineral version of SAF-XA (white bottle).

[someonestolecc]

Ahh thanks. Oops didn't realise it's gearbox oil haha I have found my gearbox oil atleast!

Thanks for that I will go for the motul PA90 - it's cheaper anyway and the redline they said I will need to bring my own container cos they dont have bottles of it.

How many litres will I need you think?

[Busky2k]

2L is enough! Im suprised they dont sell Redline in containers.. Sounds a bit dodgy...

[someonestolecc]

err thats meant to read "UAS said for the redline I'll have to bring my own container".

The guy said they only use it in the workshop and not sell it but happy to sell from the drum (or whatever) they got if I bring my own container.

Sweet I'll just get 1 bottle then. Is it worth cycling diff oil or no? I know it hasn't been changed for a very VERY long time and it's been (ab)used for a very VERY long/hard time