I need a gear oil history lesson!

[CTF]

I'm curious about the evolution of gear oil.

I have several Farmall tractors from the 40's and 50's. The original manuals call for 90w oil in the trans/rear. In the mid and late 50's IH came out with the Torque Amplifier (basically a gear splitter utilizing a planetary gear set and wet clutch that preceded the transmission) and lighter universal trans/hydraulic fluid was born to give better performance. The transmission and final drive were still the same design however.

I've been using GL-5/MT-1 as a replacement in non T/A applications but I'm a little bit concerned about formation of corrosive elements due to moisture and the EP additives required of GL-5. The shared case for the trans and final drive tend to collect moisture over time due to surface area available for internal condensation, even when stored out of the weather. Some are using the UTF fluids with no obvious ill effects, but there are no wet clutches or brakes or shared hydraulics on the earlier tractors that would make it a requirement.

Except for the reverse idler shaft, All shafts run on ball bearings. The reverse idler uses steel backed bushings. The gears are sliding type, straight cut. R&P are bevel straight cut.

I'm wondering where 90 weight refined in 1950 would fall on GL scale we use today and how it would compare even against motor oil in comparable weight and additives. What would be the viscosity of a typical UTF type fluid? And why is UTF always labeled as such and such "fluid" instead of "oil"? Is there something to the nomenclature? Would certain motor oils merit consideration as gear lubricant in this case?

 

[oilboy123]

Very good questions...... I sure you will get some answers to, just not from me. Be patient others will chime in.

 

[Jim Allen]

CTF: First some terminology and a little Tribology lesson. My pardon if you already know this.

Engine oils and gear oils use different grading systems, so the "30" of an engine grade has no relation to the "90" of a gear oil grade. Remember the "90" is a grade, not the actual viscosity. A grade will run a range of actual viscosity as measure in Centistokes (cSt). In fact, a typical 40 grade engine oil is the rough viscosity equivalent of 90 grade gear oil.

Do you mean "UTF" as the "Universal Tractor Fluid" that was a 40 Grade engine oil oil that could be used in the engine, trans or whatever? These were popular 20+ years ago but are becoming harder to find these days.

Or, do you mean "THF", "Transmission Hydraulic Fluid," like HyTran, the stuff that can be used on tractors that have a common sump for the trans, final drive and hydraulics. THF is approximately a 20 grade engine oil (approximately 80 grade on the gear oil chart). It's essentially a thick hydraulic oil with the anti-wear additives normally used in gear oils.

Based on the few VOAs and info I've seen, the UTF (my definition above) was a compromise that was so so in both category. The THF, is a better choice from the additive area, but it's a little light on viscosity compared the the 90 grade you are using now. If you don't work your tractors hard, the THF should be fine. I use it in my 40 year old Farmall 826... and it works! But then it was designed for it.

I don't know enough to comment in detail on gear oils of the '40s and '50s, but I do know that oils have improved radically in the ensuing years. I'd be willing to bet that a THF is every bit as robust as the oils of old, which likely sheared down thinner fairly rapidly. Vis-a-vis the corrosion aspects, modern GL-5s are pretty mild compared to what they once were, so in reality, you probably don't need to be afraid of them either. Some are even GL-4/Gl-5 dual rated.

Given that you have very little in the tractor to worry about, I think you are safe either way. Me, I'd probably use HyTran but If I had it full of GL-5 now, I'd run that out first.

 

[MolaKule]

Hi CTF,

Some time ago we had written a number of White Papers on Gear Lubes that you will find down in the Science and Technology of Lubricants and Additives section such as:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=729255#Post729255

So please read these and ask away.

 

[MolaKule]

You may be tinking of Universal Tractor Hydraulic Fluid or what we call UTTO's?

Some tractors have separate geare boxes that use only say a 89W90 gear lube and a separate hydraulic pump and hydraulic fluid for implements, and some (more modern units) use a Universal Tractor Hydraulic Fluid for both gear boxes and the hydraulic system.

The spec I have for a UTHF (mostly a Blend) is that it has a viscosity of 9.5 to 10.5 with an AW and other additive package about the same as an older HDD oil.

A 80W90 gear lube has a viscosity of about 15-18 cSt so it is a much thicker lubricant. The GL 5 spec is essentially a load/wear performance spec that includes an EP package for heavy gear loading and mainly speced for highly loaded offset gearing such as one would find in a hypoid differential.

An oil is a specific fluid that lubricates.

A fluid is a substance that flows relative easy.
With the exception of a grease, which is a semi-solid, most lubricants are fluids. Petroleum oil is a fluid. Synthesized oils are fluids.