Best gear oil?

[drdon]

What is the recommended gear oil for 1937 trans w o.d. 90? 140? I read a lot of variance. 

PS: sticking with GL4. 

[Spinneyhill]

MoToR's 1947 says SAE 70 in summer and 50 in winter. Shop manual says this too.

 

If you use an oil containing EP additives, as there are in GL4, make sure the copper strip corrosion test result is 1a. 1b will pass muster, but only just. Try for 1a.

Edited July 15, 2019 by Spinneyhill (see edit history)

[drdon]

What about Sta Lube 85-90 GL-4?

Heard about it on another site. 

[Gary_Ash]

Most auto parts stores carry Synchromesh fluid for manual transmissions.  I usually get the Pennzoil brand.  It's rated for transmissions with brass or copper parts.  Otherwise, non-detergent straight 40 or 50 weight oil is fine.

[Spinneyhill]

16 hours ago, drdon said:

What about Sta Lube 85-90 GL-4?

Heard about it on another site. 

And those on "another site" were experts, yes?

 

Try to find the ASTM D130 (Copper Strip Corrosion Test) data about that stuff. I can't. If it has EP additives and you can't find the ASTM D130 test results, don't use it. Simple.

 

The manual says SAE 70. Use it! No EP additives. I believe there are bronze baulk rings in the gearbox and there is probably a big bronze part in the overdrive.

 

I wouldn't use "non-detergent" = oil with no additives because it will turn to sludge with use and also will foam.

[drdon]

Bought GL-1 Ford Tractor gear oil (90w) at Tractor Supply. Thanks all.