1986 international s1900 w/ eaton fuller T14607a Direct drive

[Autodiculous]

so eaton fuller recommends a straight 50 weight oil for this trans. I have a few questions:

Why specifically a straight 50 weight?

Could I use something like a 15w50? could the 15w50 be an engine oil since I have not been able to find a 50 weight mobil 1 or equivalent fully synthetic gear oil or is there missing additives / corrosive additives that would not be good for a trans in that engine oil?

Is there a synthetic straight 50 weight that is as reliable as mobil 1 fully synthetic gear oil?

Thank you for help, pointers, and opinions!

 

[krismoriah72]

You can buy the straight 50 transmission oil at almost any truck parts store. Its very common. But Kind of Expensive. $150/ 5gallon


On my older 10+ year old trucks i used 80w90 which is very similar viscosity.


15w40 in the engine, 80w90 in trans and 85w140 in the rears just keeps things easy.

 

[Rob_Roy]

Use the recommended 50w oil. The additive package is different than the other products you mentioned. Synthetic products are available, but more expensive and likely not needed for your application.

 

[AITG]

As a former fleet operator, I have seen both 50 wt and 90 GO used in Fuller transmissions. IIRC, the concern Fuller had with 90 wt. gear oil was that it was not as effective on synchronizers as the 50 wt. Since you don't have synchronizers (no range shift). Use whatever you choose.