NP 205, ATF or Gear Oil?

[SquareRoot]

Np205- Gear Oil vs ATF
It seems at some point, mid-80's (?) GM switched the fluid in the 205 from gear oil to ATF. Anybody know why? Was it an efficiency thing or does ATF actually perform better? Personally, I'd think gear oil would protect an all steel gearbox better but what do I know.

 

[Bextreme04]

Np205- Gear Oil vs ATF
It seems at some point, mid-80's (?) GM switched the fluid in the 205 from gear oil to ATF. Anybody know why? Was it an efficiency thing or does ATF actually perform better? Personally, I'd think gear oil would protect an all steel gearbox better but what do I know.

Yep, they changed the spec in the 80's when they went to the round pattern adapter. I've read a bunch of different things on this and it seems that plenty of people run both and have no issues. I use 80-90 because mine gets garbage MPG anyways and leaked a bunch with gear oil, I didn't want to see how bad the leaks would be switching to ATF.

 

[SquareRoot]

That's my

Yep, they changed the spec in the 80's when they went to the round pattern adapter. I've read a bunch of different things on this and it seems that plenty of people run both and have no issues. I use 80-90 because mine gets garbage MPG anyways and leaked a bunch with gear oil, I didn't want to see how bad the leaks would be switching to ATF.

That's my thoughts as well. Milage doesn't concern me. I know the guts are all the same regardless of year. I have early guts in a round pattern case. To me ATF is like water. I can see it in an automatic but I prefer gear oil in a gearbox. Thanks

 

[bucket]

Iirc, they went to ATF when the "synchro" 205 went into use and auto hubs became available. So it would have been when the figure 8 pattern case was still in use.

 

[SquareRoot]

Iirc, they went to ATF when the "synchro" 205 went into use and auto hubs became available. So it would have been when the figure 8 pattern case was still in use.

Makes sense. Since mine is non synchro and manual hubs, I'm gonna go with gear oil.

 

[bucket]

Makes sense. Since mine is non synchro and manual hubs, I'm gonna go with gear oil.

I guess I should clarify. I don't remember if all of them in those auto hub years ran ATF, or if only the syncro 205's ran ATF at first.

 

[Dooley]

T case and Differential Lubricant recommendations Lubricant recommendations

The service manual I referenced calls for Motor oil For the transfer case if it is full time 4 wheel drive and Gear oil if not. I believe my 1977 blazer was born with full time And was modified by a previous owner. I bought it with manual locking hubs. Does anyone know what I should be using...

www.gmsquarebody.com

Excellent info in this thread in previous thread..
GM had a us run 10W30/40 weight motor oil in the 205 in 1980 after earlier gear lube and before ATF.
My 1988 V30 squarebody was ATF.