The Stovebolt Site Forums The Shop Area Driveline 80W-90 in 4-speed?

Good morning Stovebolters.

I've had a hard time finding 90 weight mineral oil here locally, and wondered if 80W-90 is ok to run in my SM-420 4-speed. The closest thing I've found that would probably work is at Tractor Supply; 90 weight mineral "Traveler" brand Ford tractor transmission oil. This would probably work just fine wouldn't it?

Yes , the Tractor supply mineral oil is the correct oil to use as it is the mineral oil that many on this site swear by. Others more knowledgeable would tell you that the some of the newer oils don't work well with the brass synchros.

The SM-420 is a pretty forgiving transmission, but it's got big, heavy gears with enough inertia that the synchronizers have a problem matching gear speeds when shifting. Stay away from the super-slippery synthetic lubes that might not let them do their thing. The Tractor Supply 90 weight mineral oil sounds like the best choice, and it's probably a lot less costly than the fancy Moose Juice to boot! Use it in the transmission only- - - - -it won't have the hypoid lube additives the rear end needs. The 80W-90 would be a better choice there, or any general purpose hypoid gear lube.
Jerry

Makes sense, thanks Jerry. Rear diff flush is coming up, so I'll pick up some 80w-90 as well. It's purring like a kitten

According to my '48 owner's manual, a single number like 90 (w/o the W) is a defined viscosity at 130 deg F. The W indicates a viscosity scale determined at 0 deg. The 80W-90 gives the extra cold info but it seems to me the 90 mineral oil has a W number that could be measured but it just isn't given.

I mean, 20W-20 used to really puzzle me.

I haven't bothered to Google the modern definitions and I'll just rely on my owner's manual. I use the 80W-90.

If they tested straight 90 weight gear oil at 0 deg, it would probably come out at about 140W-90 (yes, you read that right ).
So 20W-20 would be the same viscosity at both 0F and 130F.
I ran 140 weight in my Model A (Straight Tooth non-synchronized) tranny. Then I got clever and put some STP oil treatment in it. One morning it was in the 30's and I nearly bent the shift lever trying to get it into gear.

Not sure exactly what specific 80W-90 oil you are referencing, but many of the gear oils on the shelves of auto parts stores (at least the ones by me) contain an API service rating of either GL-4, or GL-5.

While the EP (Extreme Pressure) additives contained in GL-4/5 rated gear oils are great for reducing wear in hypoid gear sets, most are not particularly friendly to any yellow metal components in the transmission - i.e. synchronizer blocker rings....

The following link has a lot of interesting information on this topic:

Gear Oil

While there are exceptions, many of the data sheets for these oils contain similar warnings.

At one point, I might have leaned toward finding one of those "exceptions", but after looking at some of the spec. sheets for some of the plain old 90 weight GL-1 oils, it looks like the manufacturers are putting in a pretty substantial additive package (corrosion inhibitors, anti foaming, etc.).

That said, here is the data sheet for the "Tractor Supply Traveler Ford Tractor 90 weight oil".

Ford Tractor Oil

While the top of the data sheet says "API Service GL-1" (which is good for you) , further down the page it says: "Performance Standards: GL-4" - which is confusing to me. If it meets GL-4 performance standards, does it include any EP additives?

Perhaps you could shoot them an email telling them your application and see what they say. The fact that many on this site are already using it without any issues is obviously good sign, but it would not hurt to double check.

Best Regards....

Besides Tractor Supply, NAPA also carries 90w Mineral gear oil API GL-1. Besides, do you really want to use a oil designed for Fjord Tractors in your Chevy gear box ? Ewww! LOL

PSC.Com carries 5gal buckets of 90w gear lube. Thats what i use. And its nice to have it available at home when you decide to change trans or differential lube on an off time.