Caterpillar power shift transmissions used HDEO for a very long time. Around the early 90s however, the additives in diesel engine oil had become too good in some ways, as they didn't allow enough friction for the transmission clutches to work like they used to. A newer lubricant was introduced, "TDTO" transmission drive train oil, this fluid allowed for proper friction in the newer transmissions. TDTO is backwards compatible with older machines, but a great plenty of the machines built through the 1980s are still using HDEO as it is cheaper.
The hydraulics on Cat and a lot of other equipment through the 80s and in some cases later spec SAE 10W engine oil.
I've worked at John Deere dealers off and on since the late 1980s, while never on a Deere, I did run accross a few off brand tractors that specked 15W-40 for the transmission and differentials.
The first Caterpillars with torque converters actually used diesel fuel out of the fuel tank, the next model went to engine oil.
Last edited by D45678; 10/23/19 12:20 AM.