Diff oil level

[guye]

Originally Posted by Modena

I haven't purchased any so I am not sure (my diff was purchased brand new and was already filled), but I believe if you get the OE specified oil from Holden for your ZF diff it is all in one container (by the litre), I assume it would already have the additive in it, or was designed like that from the get-go. This is what I meant when I said the right oil. I think it's about $70 / litre.

This oil I bought, Ben, was specified by a) the Holden dealer, b) the lookup computer at Autobarn, c) my Pace manual, and d) my trusty mechanic (although he still doesn't believe I'm going to finish building a car!). Got four sources telling me the same answer - now that NEVER happens. Suss or what!

The additive choice was less scientific, I confess. Only one I found that I recognised (and respected) the brand name of!

Btw, all those oil recommendation sources also recommended that I should put additive in as it's an LSD.

[patrickt]

After thoroughly researching the issue, I can now confidently report that using synthetic lubricants in a Jag based differential will either 1) Help them; 2) Hurt them; or 3) Have no real effect on them. On this, I am quite sure.

[stephen low]

Ah but Patrick is this with or without the additive included??

[oilman]

Not all LSD's require an additive, only those that involve friction based designs such as clutches. These are the most common designs but there are others that for example just use gears (eg Truetrac). The additive is a friction modifier that gives the correct degree of slip and therefore prevents shuddering etc. The safest bet is to probably go with the OEM's recommendation but that's not always possible. If it isn't, then a 75W140 LSD oil is probably the safest bet followed by an 80W140. A 75W140 will definitely be synthetic in nature and most likely the 80W140 will be as well. There is no downside to using a synthetic (other than cost), only upside from a performance perspective. The treat rate of the additive (depending on the actual additive) is generally in the range of 3-6%. For example in the Holden/Ford V8 diffs, it was common to have to use 6% of the Sturaco 7098 so some manufactures (eg Nulon) now add 6% to the oil you can buy so no more additive is required. Many diff builders still swear by just using the LS90 mineral oil in everything, but I don't agree.