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When the industry recommends 80/90W gear oil I would use that.
Hey folks, this is not intended to resurrect "the great debate" relative to people's
opinions on what should be run in the NP205. Instead I provided the inquirer with a clear and irrefutable set of facts from the vehicle manufacturer and fleet owner on what they specified for use.
It is true that prior to I believe 1981 GM specified 80W+ Gear Oil for the 205. But after that date it was Dexron II (or better) exclusively.
I know that the vehicle manufacturers typically requested different specs on the products they ordered from their suppliers and therefore cannot state whether or not something was changed in the newer GM TC's that either required or made possible the use of ATF. I also do not know if ATF's were made "good enough" for use in the TC's and that is why the specification changed. I do know what is documented.
Rusty, your documents come from a 3rd party source and the second pre-dates the cut over. They are not from New Process, GM or the military. Just an observation.
People often don't realize that automatic transmissions tend to run a lot hotter than TC's and have similar shear loads in their internal gearing. ATF's MUST meet or exceed specifications for shear resistance, wear resistance, resistance to thermal breakdown, etc. In some instances motor oils have been specified for use in manual transmissions and some esoteric TC's.
I would be interested to see if anyone has access to a formal engineering postmortem on a 205 that clearly indicates the
type of lubricant caused a failure.
As with anything, if it is your 205 you should feel free to run whatever lubricant you want to in it. If you feel better about running gear oil then do so. According to the manufacturers and the military ATF is fine for the 205's intended use.
All the best!