Dexron equivalents

[Avocet]

I need to change the oil in my gearbox (Hurth HBW 50). The manual says "Dexron ATF". Looking round, I can find some Dexron II, II, ...up to VI, but no "original" Dexron. Does anyone know if any of the later grades would be compatible?

 

[VicS]

A bit of Googling will confirm that Dexron AT Fluids are backward compatible with earlier specs

 

[Avocet]

Ta. I tried that and although most sites I found seemed to suggest that this was the case, they tended to refer from the current "VI" back to "II", but few mentioned the original. I think I'll risk it. It's only transmitting 12 HP after all!

 

[Plevier]

Strictly speaking only Dexron VI exists now as a standard. All the earlier ones have been obsoleted by the owner of the standard (GM).
However you will find many non-authorised products labelled ATF and claiming to be to Dexron II or III and any of those will be fine.
I have read that you should not use Dexron VI in gearboxes - I don't know why, but possibly because it is too slippy for cone or disc clutches. I have also heard that that is why Volvo Penta changed their gearbox and saildrive oil recommendation to 15/40 instead of Dexron, in case someone used Dexron VI, but that's not gospel.
You aren't likely to get Dexron VI by mistake - much less readily available and much more expensive!
I don't think Dexron IV or V were ever released.
Good summary here http://en.wikipedia.org/wiki/DEXRON