97 ram 1500 4x4 9.25 gear lube type? Google says 75-140 but I don’t have limited slip. Some other people say 80-90. Can’t find the fluid type anywhere in service manual or owners manual. What do you guys think or recommend?

 

It's in there, 80W-90.

 

80W90 for normal use. 75w140 if you do heavy hauling/towing.

 

Ok, I don’t do much towing or hauling but would it be a good idea to just run 75w-140 anyway in the event that I do have to tow or haul anything, for peace of mind?

 

It's more expensive, but, it won't do any harm.

 

IMHO the 75-140 is simply a better all around oil. I have a 49 Dodge that calls for 80-90 GL1 ..... I'm using 75-140 GL5.

I found a chart on the internet (must be true) It listed the oil and improvements in quality over the years .... Basically the lower number gives you the viscosity when the oil is cold ... the 2nd number is not really the viscosity when warm but the protection it offers. ..... Sooo, 75 or 80 are pretty equivalent. .... the 90 or 140, the 140 is superior in protection.

Then there is also the GL1, 2, 3, 4, 5.
Pretty much is for the additives in the oil. Newer vehicles need different additives for protection as different metals or plastics are included in the transmissions/rear ends.

There was a issue with GL5 in older vehicles several years ago. The problem was, GL5 dropped support for softer metals like brass. Many vehicles up into the 70's still had brass and they started to get transmission failures with GL5 .... The oil companies were getting sued and held responsible .... So they simply put back in the protection for softer metals.
Anyone with a older vehicle needs to read the label and see that the oil supports softer metals .... almost all do support it since it is cheaper to add it in then to get sued and get a bad reputation.

I had to do my research when looking for oil for my truck .... It calls for 80/90 GL1 .... Honestly it can be hard to find, not everyone sells it.
The reason is it is really poor quality .... nobody that researches wants it. It just sits on shelf's taking up space and eventually it does get sold.

Again just my opinion from what I have read. Many will insist to use what the manual says .... when the manual was written for that vehicle, it probably was the best. Since then the qualities have improved.

 

Honestly, it doesn't matter. Use whatever's least expensive. Dino is fine. FM won't hurt anything if it's already blended in.

 

I'm with Keith, as long as its reputable you'll be fine. I personally run 75w-90 in the front and 75w-110 in the rear of my 2500.

 

I'm currently running 80W90 gear oil in both of the front and rear Dana 60s in my truck. In the rear, I do run CRC limited slip additive to keep the chatter down on the clutches in the rear diff.