The full story on transmission/hydraulic fluid for use in N series tractors

The transmission fluid in an “N”:-series tractor lubricates the transmission, differential, rear wheel bearings, PTO and hydraulic pump drive, and it also cats as the working fluid for the hydraulic lift. In 9N/2N models, it also lubricates the steering sector and shaft system.

The owner’s manual for the 9N and 2N models specified the use of only two fluids. They were STRAIGHT MINERAL OIL SAE 90 (above freezing) and STRAIGHT MINERAL OIL SAE 80 (below freezing). Caps in original. By the time 1950 rolled around, and the 8N was the only Ford tractor, oil technology had advanced a bit, and Ford specified the use of “Mild EP GEAR OIL conforming to Ford specs M4864A (SAE 80) (below freezing) or B (SAE 90) (above freezing)” . Caps in original.

Today, if asked, Ford-New Holland will specify the use of a combined hydraulic/transmission fluid which conforms to their specification M2C134D in all “N” series models.

The original specification for STRAIGHT MINERAL OIL would conform to the present-day API gear oil designation of GL1. Although less normal today, this can still be had – it is still used in non-synchromesh truck transmissions, for example.

Ford M4864 “mild EP GEAR OIL” would conform to the present-day API gear oil designation of GL3. It contains some Extreme Pressure additives (sulphur and phosphorus compounds) which make it a better lubricant for transmissions and for bevel-gear final drives where there is high-pressure sliding contact. It should be noted that the EP designation refers to contact pressure between moving parts – it has nothing to do with hydraulic pressure.

Combined hydraulic/transmission fluid is a compromise product. It contains many additives to make it work reasonably well as a hydraulic power transmission fluid, as a hydrostatic power transmission fluid and as a gear lubricant. It is not typically specified by SAE viscosity number (or “weight”) although it may be.

The Ford M2C134D fluid, for example, is not specified by SAE “weight” although its viscosity is defined by maximum numbers on various scales at various temperatures. Its viscosity on the SAE scale, based on those numbers, would be between 40 and 50.

True hydraulic fluids – fluids intended only for hydraulic and/or hydrostatic power transmission - are also typically not specified by SAE viscosity number. The ATF familiar to every driver with an automatic transmission, for example, carries no SAE viscosity number – instead, it is specified by a whole range of performance requirements, of which its viscosity is just one part. True hydraulic or hydrostatic fluids are typically of the order of 10 to 20 on the SAE viscosity scale. So there is no such thing as "SAE 80 Mild EP hydraulic fluid", for example.

If we go shopping at TSC, for example, we will find two types of fluid for our “N”-series transmission/hydraulic application on sale. One is marked “Ford Tractor Transmission Fluid – High quality oil for use in older Ford tractors”. This is the original stuff, almost. It has an SAE viscosity number of 80W90. It is not “straight mineral oil”. The sniff test tells us that it has sulphur additives, so it is at least an API GL3 gear oil. Most likely, it is an API GL5 gear oil, because that’s the universal automobile standard for gear oil these days. It is exactly the same type of oil that would be used in a conventional automobile or truck differential, although it may not be up to the latest standard.

Our other choice is “Universal Tractor Hydraulic Fluid”. This is a pig of a different grunt. It is a 10W20 oil (much thinner, and multigrade) which is “recommended” for use in place of the Ford M2C134D, as well as a whole list of other manufacturers specifications. Note that it does NOT say “Meets Ford M2C134D specification” – it can’t do that, just based on the stated viscosity alone. This oil does have an additive package which is intended to make it work reasonably well as both a gear lubricant and a hydraulic fluid.

We may also see “Hydraulic fluid” on sale. This is something else again. It is not intended for use in transmissions or final drive applications, and indeed it says so in big letters on the jug. This is for hydraulic systems ONLY. As it happens, it is marked with an “equivalent” SAE viscosity number of 20. It should be noted that there are no such designations as “EP” or “mild EP” for hydraulic fluid, and indeed, API and SAE don’t really get into specifying hydraulic fluids at all – some of their tests and standards are sometimes used for hydraulic fluid, but the full specifications are typically originated by the makers of hydraulic equipment. To use this in an N transmission would be quick and sure death for the transmission and differential - it simply lacks both the viscosity and the additives required to do that work. The hydraulics would probably work quite well using this, though.

TSC is not the only game in town, but broadly the same choices are available at your local ag supply store. The “universal” transmission/hydraulic fluid is perhaps the least best choice. It attempts to meet fifty different manufacturers specifications in one fluid. Some of those specifications are mutually exclusive – as will be seen in the example of viscosity noted above. It would, however, be a good hydraulic fluid for a hydraulic lift system in good working order. The originally-specified 80 or 90 weight gear oil is probably a better transmission and final-drive lubricant – the downside is that it is not so good as a hydraulic fluid, especially in cold weather. For those reasons, a combination transmission/hydraulic fluid which does conform to the Ford M2C134D spec is probably a better compromise between hydraulic system performance and gear lubrication.

That's the straight dope. Sorry it's so long, but it's a multi-facted subject, and obviously it's hard for some to understand. Additions and comparisons with other products available in other parts of the country, from those who know what they're talking about, are welcomed.

llater,

llamas

I have just purchased a 41 9N and need to change the transmission oil - it is milky tan. Can you tell me the required amount of oil to purchase?

Also, I notice there are two drain plugs, one lined up below the seat section and the other below the shifter section. Are these both the same fluid? And if I drain both, do I have two refill plugs??

Thanks in advance for any help!

Pigue

I have one question however. Since there does not appear to be any one fluid that is perfect for the combination of gear lubrication and hydraulic system in the summer and winter both would a mixture of 50/50 85W140 GL5 gear oil and Ford's M2C134D spec oil be better. My thinking on this is that the heavier gear oil would increase the viscosity of the M2C134D spec oil while the M2C134D spec oil would kept it from getting too thick in the winter.

Also I would think the GL5 oil would be a lot better gear oil than the old straight mineral oil.

I mostly do light bush hogging in the summer in 90-100 degree weather and would like to use my tractor for occasional snow removal in the winter, normally around 15-30 degrees.

Any thoughts on this or am I off in left field somewhere.

Just what I've always claimed, M2C-134D is my tranny oil of choice because of the additives of EP-90 oil, it is not the same 90 wt "mineral oil" of 1930's & 1940's.

I've seen what EP-90 can do to a BMW tranny's brass syncromeshes, turns a hot knife thru warm butter shifting tranny into a real gear grinder. Non-warrentee-able (you can smell the additives). In 1975, the customer really complains about the $1200 rebuild fee. My parts man had to "import" the correct tranny oil which was not the same as the hypoid differential oil.

Thanks..... Dell

Straight mineral oil (GL1) has no additives of any sort. Anything described as "hypoid gear oil" (which would be at least GL3 grade) should have at least some. "Hypoid", incidentally, doesn't refer to the oil, but to the type of gears it's good for - the differential gears in your N, for example. Any "hypoid gear oil" rated GL5 will have some anti-foaming agents in it.

I wouldn't worry about the lack of them in any case. Nothing in the rear end runs fast enough for this to be an issue, and the air space is so huge, and the volume of oil so large, that it's doubtful that you could turn a significant amount of it into foam. The pump is completely submerged, so no problems there. The transmission shouldn't need them either.

llater,

llamas

I presume that Llamas did not have access to the Aug. 18, 1948 or Mar. 1, 1949 manuals or he would have commented on the motor oil option. None the less I feel sure that it would be within the relm of things he noted regarding the various "proper" oils for the N-Series.

EXCELLENT post as usual, Llamas. THANKS!!

Regards
Larry
8N75381

Maybe that explains why they recommended the use of lower-viscosity oils for a couple of years in the late 40s, then backpedalled to a higher viscosity, with EP additives, in 1950 and on. The EP additives speak specifically to the differential gearing - that's where they'd do the most good.

Anyone else have better data?

llater,

llamas

Jumping forward to current manual transmissions, many of the manufacturers are specifying motor oils or even ATF for their transmissions. This can, and does, work; provided the owner is rigorous in changing the transmission oil on schedule. Something most people do not do. It reduces drag, increasing fuel economy. With many of the tiny cars, the loss of EP lubrication is not a significant issue; again, provided the oil change intervals are adhered to without fail. Most motorcycles lubricate their transmissions with engine oil btw, and have for many decades.

Taking that and jumping backwards, the knowledge of the basic oil similarities existed in the 1940's. If there was a problem with the availability of the typically specified gear oil at that time (wasn't around then, don't know), Ford may have been officially acknowleding a make due alternative oil. Though why it was listed first, and not as a poor second choice, I do not know. Alternatively, it may well have also been to do with an error of engineering understanding by a marketing type or such that was later corrected. I do not know, just rumenating on the subject.

Secondly, a lot of folks have said (in some form of words or other) that the SAE viscosity number scales are "different" for gear oils and crankcase oils. By outcomes, this statement is true, but saying it that way might lead someone to think that there are two different scales when there are not.

SAE viscosity is SAE viscosity. What's different is the temperatures at which viscosities are measured. Viscosity reduces as oil gets warmer - how much it reduces is defined by its viscosity index. Oils defined as "gear oils" are specified by viscosity at 150°F. Oils defined as "crankcase oils" are specified by viscosity at 210°F. So,for example, a gear oil with SAE viscosity 90 , at a given temperature, will have the same viscosity as a crankcase oil with SAE viscosity 40, at the same temperature.

Put another way, heat SAE 90 viscosity gear oil to 210°F and it will flow like SAE 40 weight crankcase oil.

The basic difference between "gear oils" and "crankcase oils" is that you can't get plain old mineral oil to do what's required at crankcase temperatures without additives - additives which stabilize the viscosity of the oil and keep it high enough at high temperatures to do its work. If you needed 40 weight oil in a motor at operating temperature, for example, without viscosity enhancers, it would be molasses in the motor when it's cold. Viscosity enhancers reduce the amount by which viscosity changes with temperature (improve the viscosity index).

Gear oils may have some viscosity index additives, but they're relly not required because the temeperature differences are not nearly as great as they are for crankcase oil. Gear oils also have another much more critical function, and that's taking care of very high pressure contact/sliding friction - between gears, especially hypoid and bevel final drive gears - at high torque and low speed. To this end, they contain lots of friction enhancing additives - sulfur and phosphor compounds. Crankcase oils need much less of this because most of the lubrication in a motor is hydrodynamic - the surfaces don't touch like they do in a transmission. The downside of these additives is that they can be corrosive (especially to bronze and alloy bearings), and they should never be used in a crankcase, even if the viscosity has been "corrected" for temeperature difference.

So, in summary, gear oils and crankcase oils are measured under different conditions. It may be useful to understand the scale differences - what's the viscosity of an SAE 90 gear oil in terms of a crankcase oil number - but it doesn't tell you very much. It's more important that you be sure that you have the right stuff - look beyond just the SAE viscosity number.

llater,

llamas

If you don't mind, I'd like to further clarify (confuse?) two points that seem to need it;

1, When you compared SAE 90 gear oil at 210 degrees F and said it will flow like SAE 40 engine oil, both oils are at 210 degrees F.

2, When you referred to viscosity enhancers with regards to the SAE 40 weight motor oil so that it wouldn't pour like molasses when its cold, you were refering to making it a multi-weight oil. Like 10w40. There are no viscosity enhancers in straight weight oils. It's just the multi-weight oils that use them.

There is a down side to using viscosity enhancers. They make the oil weaker. The wider the span, the more easily damaged the oil molecures are. A straight 40 weight will hold up better to shear and heat then a 20w40. And a 20w40 will hold up better then a 5w40. The wider the span, the weaker the oil. I bring this up as a point only because multi-weight oils are common here. People do need to use care and judgement on how wide a span then need based on their climate conditions.

SAE has once again changed their web page, and now locked everything away, so I can't link to them directly. But the attached link has right at the top a good graph showing the relationship of gear oil and motor oils at 100 degrees C, which is what I was trying to describe. It also contains a heck of a lot of general oil information, from an undisclosed time in the past (it's dated, so use the information with care).

• Everything you never wanted to know about oils.

Also, is this list complete?? What is the number on the 1951 manual? It will be something like 3729-51-?? i.e. what is the letter at the end?

tia
Larry
8N75381

Printed and filed. Thanks again.

llater,

llamas

My LBC (little british car) and I thank you!

This wouldn't be the first time Ford saved the day either. Ford makes the best DOT3 brake fluid, in the form of their Heavy Duty Truck fluid.

Have a care and look for the grade marking. The "mild EP" gear oil which Ford specified from 1950 on would be a GL3 equivalent. That's not to say that what's sold today for that application meets the GL3 spec - I suspect it would be GL5 or equivalent. But I have no evidence of that. I do note, for example, that my local TSC sells the 80W90 oil "for older Fords" at about $3 for 5 gallons MORE than rated, plated GL5 80W90. So maybe it is different, but in what way, who can say?

Have a great day.

llater,

llamas

Original Henry liked splash oiling - the original Model T had no oil pump, for example, and everything was oild by just throwing it around a lot.

llater,

llamas

Please, keep EP gear lube as one topic and mineral oil as a hydraulic power transmission substance separate in your thinking. IHank