Transmission oil or Gear oil in transmission?

[Soupermike]

I am totally confused on what to put in my transmission. I have been reading many posts about what people are using in their trucks (mostly deuces) and the discussions say to stay away from GL-5 because it attacks the yellow metal and others say it doesn't matter because it needs a high temp to activate the sulfur which leads to damage. I have also seen the posts saying to use 85w-90 gear oil. What are y'all using in your M37s?
Thanks
Mike

 

[Roller]

I am totally confused on what to put in my transmission. I have been reading many posts about what people are using in their trucks (mostly deuces) and the discussions say to stay away from GL-5 because it attacks the yellow metal and others say it doesn't matter because it needs a high temp to activate the sulfur which leads to damage. I have also seen the posts saying to use 85w-90 gear oil. What are y'all using in your M37s?
Thanks
Mike

I use 85w-90 gear oil.

Frank

 

[Soupermike]

Do you have a preference on what GL spec you use?

 

[Roller]

Do you have a preference on what GL spec you use?

GL 4 is what I have used, although GL5 could be used also. As I recall the syncros in the NP420 are aluminum not brass.

 

[M35A2-AZ]

I started used this in my Deuce and M37. Been working well. It is a GL-4, It is a Sta-Lube
CRC 24239 Multi-Purpose Gear Oil 85W90 SAE

 

[John Mc]

When I rebuild mine, I think I'm going to try the Amsoil SAE 50 synthetic transmission oil. Charles at M Series Rebuilds seems to be a fan, as are several others with whom I've spoken. I've got 85W-90 gear oil in the transmission now. It is really stiff in the winter and takes a while to loosen up, even when it's just moderately cold out.

I just tried the Amsoil Z-ROD 10W-30 engine oil at my last oil change. It's not cheap, but I was curious if I would see any difference. I did notice that the engine seems to be running about 15˚F cooler (even with the warmer ambient temperatures we are seeing now).

Lubes have come long way in the almost 70 years since my truck was new. IMO, there is no good reason not to take advantage of the advances, particularly in a transmisson, where lube change intervals are so long.

 

[Soupermike]

I think I am going to use this as I can get it locally. Thanks for the info/help.