The Ford Barn

Ramblin Reck · 10-10-2021, 09:52 AM

I understand that a Hypoid, 90W, NON-SYNTHETIC Gear oil is best for this vehicle's transmission. Even 75W/90 is fine. Finding it is proving difficult for this rookie. The objection to Synthetic GL5 is that it eats up the brass over time.

One suggestion is to buy Tractor Supply straight mineral oil and add 25% Lucas oil extender available at Walmart. Anybody else use this concoction?

O'Reilly's Auto Store recommended Pure Guard GL-4 140. They also recommended ordering A Valvoline Quart bottle that specifically said "real" oil, not synthetic.

I did not think that it would be this difficult to "buy" the correct transmission gear oil for this 1939 Ford.

Reading the instructions in my Ford Passenger and Commercial Reference Book 1939 it specifically says to Drain, Flush and Refill with Gear Oil:
Winter S.A.E. Viscosity 90
Summer S.A. E. Viscosity 140

Also by "Flush" I assume it means to overfill with oil and let that flush out the old gunk.

10-10-2021, 09:52 AM	#1
Ramblin Reck Senior Member Join Date: Jul 2021 Location: Savannah, Georgia Posts: 245	1939 Ford Transmission Gear oil I understand that a Hypoid, 90W, NON-SYNTHETIC Gear oil is best for this vehicle's transmission. Even 75W/90 is fine. Finding it is proving difficult for this rookie. The objection to Synthetic GL5 is that it eats up the brass over time. One suggestion is to buy Tractor Supply straight mineral oil and add 25% Lucas oil extender available at Walmart. Anybody else use this concoction? O'Reilly's Auto Store recommended Pure Guard GL-4 140. They also recommended ordering A Valvoline Quart bottle that specifically said "real" oil, not synthetic. I did not think that it would be this difficult to "buy" the correct transmission gear oil for this 1939 Ford. Reading the instructions in my Ford Passenger and Commercial Reference Book 1939 it specifically says to Drain, Flush and Refill with Gear Oil: Winter S.A.E. Viscosity 90 Summer S.A. E. Viscosity 140 Also by "Flush" I assume it means to overfill with oil and let that flush out the old gunk.