Allison transmission oil 15/40wt ?

[To it and at it]

My local factory Allison shop insists that we use Dexron III that meets Allison's spec TES 389. Other oils may lead to seal problems.

[NealinNevada]

Matt, interesting that you bring up TES 389 spec. I am looking at this Service Information Letter from Allison (dated 8/2011) and it states:

DEXRON® III and DEXRON® VI fluids are no longer approved for use in Commercial On Highway transmission products and have been removed from the Allison Approved Non-TES 295 or Non-TES 468 fluids list.

[rrueckwald]

Originally Posted by NealinNevada

FYI, all oils are backward compatible. So Dexron VI (the newest iteration) is compatible with all previous versions of Dexron.

I believe that the oil must meet Allison C-4 designation...Dexron III does (as well as IV, V, & VI).

Neal,

As I understand it, backward compatible does not mean forward compatible. I wouldn't put Dexron VI into any Dexron III machine.

Seems like we need an oil expert here.

[NealinNevada]

Originally Posted by rrueckwald

Neal,

As I understand it, backward compatible does not mean forward compatible. I wouldn't put Dexron VI into any Dexron III machine.

Seems like we need an oil expert here.

No, all new oils have to be able to go backward (i.e. backward compatibility) in time. That is Dexron VI can be used in a unit specing Dexron III. Dexron III should not be used in a unit that spec's Dexron VI however. As an example...Dexron VI has a lower viscosity than Dexron III does, but it is so much more resistant to shear, that after Dexron III is used a short time it has the same viscosity as Dexron VI. Therefore, Dexron VI can be used in a older vehicle specing Dexron III....but...you can't use Dexron III in a tranny that specs Dexron VI (it would be to high a viscosity).

[To it and at it]

Originally Posted by NealinNevada

Matt, interesting that you bring up TES 389 spec. I am looking at this Service Information Letter from Allison (dated 8/2011) and it states:

DEXRON® III and DEXRON® VI fluids are no longer approved for use in Commercial On Highway transmission products and have been removed from the Allison Approved Non-TES 295 or Non-TES 468 fluids list.

The main point they stressed was TES 389, no matter what type of oil you use. If it says 389 on the bottle, you're good to go. I'm talking MT643's here.

I used a Valvoline product lately that meets the spec.

[Rollin' OldSchool]

The only reason i was asking is I had to reseal the torque converter and the input shaft seal so had to drain the fluid, so I guess im going back with dextron since I didn't rebuild the whole trans and the othere seals are use to it

[rwoody]

all military Allison use motor oil!

seen a bunch of humvee with it too~!~