There has been a great debate on proper lubrication of certain components so I have come up with a little bit of lubrication tech for those of you that do not know exactly how different lubricants work, motor oil, gear lube, and tranmission fluid. This should help you make a knowledgeable decision when choosing your next lubricant.


Lubrication can be a daunting obstacle to someone unfamiliar with the basic concepts. Even someone with experience can be confused by the technology of current machinery combined with the multitude of lubricants available on the market today. Reviewing a few basic principals of lubrication can make it easier to see why lubrication is necessary in every application.

Friction
Webster’s defines friction as the “the rubbing of one body against another,” and as “resistance to relative motion between two bodies in contact.” Friction can be beneficial. As we overcome this resistance to motion between two objects in contact, heat is generated. This heat is what warms our hands or starts a fire. Friction is also the principal behind the braking systems we find on our automobiles. In fact once we were able to get a car moving, there would be nothing to stop it without friction except the effects of gravity or other objects.

However friction can also be our enemy. The heat generated as a result of friction can cause damage. Because contact is required to cause friction, wear in the areas of contact can occur. This can lead to material failures, overheating, and the formation of wear deposits.

Although there are many ways to reduce friction, the most common way is through the use of a fluid or semi-fluid material. The key characteristic of such material is that they are not readily compressible. Fluid and semi-fluid materials allow us to minimize component contact or eliminate contact altogether. These fluids are commonly referred to as lubricants.

Types of Lubrication
There are three types of lubrication situations that can exist between two surfaces separated by a lubricant. Whether or not these situations occur is dependent on the ability of the lubricant to provide adequate protection to the moving surfaces.

When a fluid lubricant is present between two rolling and or sliding surfaces a thicker pressurized film can be generated by the movements of the surfaces( at their respective velocities). The non compressible nature of this film separates the surfaces and prevents any metal to metal contact. The condition in which surfaces are completely separated by a continuous film of lubricating fluid is commonly referred to as Hydrodynamic or Full Fluid Film lubrication.

Although hydrodynamic lubrication is the ideal lubrication scenario, in many situations it cannot be maintained. Hydrodynamic lubrication is limited by the lubricant’s viscosity, the rotational speed or RPM and by component loading. An increase in load decreases oil film thickness.

Boundary lubrication is a condition in which the lubricant film becomes too thin to provide total surface separation. This may be due to excessive loading, low speeds, or a change in the fluid’s characteristics. In such a case, contact between surface asperities (peaks or valleys0 occurs. Friction reduction and wear protection is then provided via chemical compounds rather than through the properties of the lubricating fluid.

The third type of lubrication situation is known as Elastohyrodynamic Lubrication, (EHD or EHL). This situation occurs as pressure or load increases to a level where the viscosity of the lubricant provides higher shear strength than the metal surface it supports. As a result, the metal surfaces deform elastically in preference to the highly pressurized lubricant. This increases the contact area and decreases the effectiveness of the lubricant.

To minimize friction, an effective lubricant should be able to handle the pressure and speeds of the surface it will separate.

Continued below.

Continued

What Every Lubricant Must Do
Though the ability to minimize friction is the number one function of a lubricant, there are other major functions that must be considered. A lubricant is likely to also be required to:

Clean: A lubricant must maintain internal cleanliness by suspending contaminates from adhering to components.

Cool: Reducing friction will reduce the amount of heat that is generated and lower the operating temperature of the components. A lubricant must also absorb heat from the components and transport it to a location where it can be safely dissipated.

Prevent Contamination: The lubricant should act as a dynamic seal in locations such as the piston, piston ring and cylinder contact areas. This minimizes contamination by combustion chamber by products (for example) in the lubricating system. Lubricants are also relied heavily upon to support mechanical seals found elsewhere and to minimize external contamination and fluid loss.

Dampen Shock: The lubricant may be required to cushion the blows of mechanical shock. A lubricant film can absorb and disperse these energy spikes over a broader contact area.

Transfer Energy: A lubricant may be required to act as an energy transfer median as in the case of hydraulic equipment or lifters in an automotive engine.

Prevent Corrosion: A lubricant must also have the ability to prevent or minimize internal component corrosion. This can be accomplished either by chemically neutralizing the corrosive products or by setting up a barrier between the components and corrosive material.

Components of a Lubricant
Lubricants are generally composed of two groups of materials. The first is a base or stock fluid. This fluid will make up 75 to 95 percent of the finished product. The most commonly used stocks today are derived from petroleum crude oil. The stocks are often referred to as mineral or synthetic stocks.

To this, base or stock chemical compounds may be added to enhance or impart new properties to the mineral oil. These compounds are commonly referred to as additives. The use of such special compounds is another way to minimize friction and wear. The main role of these compounds is to offer protection when the lubricating fluid can not maintain component separation.

Bitchin!

But why in Chevy instead of Gen4x4?

Using the text above as a guide this is how we determine what products are used and to what capacity they are useful for.

For instance in an automatic tranmisison, you would want a thin viscous fluid that will dissapate heat, remove contaminates and offer some lubricity, as heat and particulate contamination from wearing hard parts are the main casue of failure in an automatic transmission. You would also want this lubricant to transfer the energy as hydraulic power.

In a gear driven transfer case, or in a rear end, the lubricant is there to act as a shock dampener, hydrodynamic lubricant, and as coating to prevent corrosion. A transmission type fluid will not offer the protective and lubricating properties that a gear oil will.

Now, the exact opposite can be said for a chain driven transfercase, where an automatic transmisison fluid would be used to maintain cleanliness, and eliminate excessive wear on chain links and pins. The auto tranny fluid would act as a scrubber, to help keep the chain links clean.

Some manufacture's recommend an automatic transmission fluid on a gear driven tranfer case, unfortunately this defies all logic and serves no purpose but to anticipate an increase in fuel savings. When in reality it won't save much when you consider the damage that is being done by the gear driven transfer case not being properly lubricated.

Just My .02,

Bitchin!

But why in Chevy instead of Gen4x4?


There has been a large debate here recently about tech and advice not being credible and I have seen some information posted in the Chevy Forum specifically about transfer case lubrication. I figured throwing this little gem out here would help elimnate any confusion,

I honestly don't give a shit who puts what in there transfercase, hell you can fill it with rocks for all I care, but for the newbs who really have no clue, this little nugget will make them think before they make a decision.

I agree Grump, someone will try and refute this as BS, but then again it's hard to ague with science.

Just trying to prove that not all newbies are ignorant to the ways of PBB, and some come bearing actual knowledge, it just took us a little longer to find the board.

In reality the OP is very much correct in his assement of what the purpose of lubrication is. And touches on the broad spectrum of different fluid types and there usage(s).

Only the smallest tip of the iceberg however.

So I have the best of both worlds in my 77 Jimmy with Turbo350 trans and 205 transfercase, it always leaks tranny fluid into the transfer case so I drain it off and refill it every so often. Pulled the transfercase once and redid the O ring, still does it. ^%$#&^#&$$&^ POS.:homer::laughing:

so, if I am reading this correctly, the thicker viscosity the oil has, the more "padding" the gear teeth will see on impact, right? Heres a question:

Do the helical teeth in a gear drive transfer case require a thicker lubricant to spread and cushion the load as it is transferred from one gear to another?

so, if I am reading this correctly, the thicker viscosity the oil has, the more "padding" the gear teeth will see on impact, right? Heres a question:

Do the helical teeth in a gear drive transfer case require a thicker lubricant to spread and cushion the load as it is transferred from one gear to another?

Well yes and no. Depends on the additive formulation that the OEM reccomends. Case in point is the NV4500.

The NV4500 calls for an additive package that in essence is a LOWER grade then the more common API formulations found off todays shelf. GL-4 vs. GL-5

Another example is the common motor oils that have the "newer" formulations that contain lessor amounts of ZDDP. Even if you compare a 5w-30 to a 20w-50 of an SJ API formulation. You will not have the additional ZDDP of an older SG API oil. Yes the 20w-50 is "thicker" but does not have the anti scrub additives of the "lower" grade SG. So the "padding" factor is different.

In reality the OP is very much correct in his assement of what the purpose of lubrication is. And touches on the broad spectrum of different fluid types and there usage(s).

Only the smallest tip of the iceberg however.


I have studied this for hours on end it's part of my job. What i covered above is just a small part of the basics.

When I get time I will add more about polyalphaolefins, ,Synthetic additives, and EP additives.

Well done, anatram. Do you think you could better explain the difference between viscosity and film strength? The two terms get thrown around interchangeably but are not necessarily...well...interchangeable. I know they are typically related, but it isn't necessarily a direct relationship.

I need to learn more about this too, so school us old bastards with info that we can use!

My understanding is the design of helical gear teeth, does spread the load more than straight cut gears, along with being quieter.

Well done, anatram. Do you think you could better explain the difference between viscosity and film strength? The two terms get thrown around interchangeably but are not necessarily...well...interchangeable. I know they are typically related, but it isn't necessarily a direct relationship.

I got this is from a friend of mine who works for a large oil company:

Viscosity is a measure of a fluid's resistance to flow. It is ordinarily expressed in terms of the time required for a standard quantity of the fluid at a certain temperature to flow through a standard orifice. The higher the value, the more viscous the fluid. Since viscosity varies inversely with temperature, its value is meaningless unless accompanied by the temperature at which it is determined. With petroleum oils, viscosity is now commonly reported in Centistokes (cSt), measured at either 40°C or 100°C (ASTM Method D445 — Kinematic Viscosity). An earlier method for reporting viscosity in North America was in Saybolt Seconds Universal — SSU or SUS — or, for very viscous oils, in Saybolt Seconds Furol — SSF (ASTM Method D88). Other less common viscosity units are the Engler and Redwood scales, principally used in Europe.

I will ask him about viscosity vs film strength.

Well done, anatram. Do you think you could better explain the difference between viscosity and film strength? The two terms get thrown around interchangeably but are not necessarily...well...interchangeable. I know they are typically related, but it isn't necessarily a direct relationship.

Viscosity is the measurement of flow between different grades of oil based on ambient temperatue and operating temperature. The viscosity of any oil changes with temperature.

The higher the temperature the lower the viscosity, it can be compared to pour point, example, when syrup is cold it is thick and doesn't pour very well, this would be considered a high viscosity oil, if you warm that syrup up in the microwave, the viscosity changes and therefore pours easier.

Now, a lower viscosity oil like a single grade engine oil 15wt, will not show as much pressure on an oil pressure gauge, but becausee it flows better it will allow the oil pump to pump more volume. The exact opposite can be said for a higher viscosity like a 40wt, the 40wt will show high pressure at the gauge, but becasue it is thicker it will not flow as well through the oil galleys.

Multi grade oils like 10W40 were introduced to counter the effects of using just a single grade oil, the multigrade allows for easier flow characteristic when the engine is cold, but will also maintains it's viscosity to a higher degree after the unit is at operating temperature.


Multigrade oils are formulated from a base stock of oil and additives are added, long branched chain polymers, that lessen the chance of viscosity change due to high temperatures. This allows a 10W40 oil to flow like a 10W at cold temperatures and a 40W at higher temperatures. Multi grade oils are formulated to pass the viscosity test across a wider range on the viscosity index scale.


Film Strength is the test used to determine the amount of pressure the oil's film can withstand before rupturing.

What this means as the oil is circulating between bearing surfaces, the hydrodynamic cusion that the lubricant provides is being sheared in opposite directions. When this shearing occurs a lubricant's film strength is it's ability for the oil molecules to stay together and continue providing the hydrodynamic cushioning.

Some people also confuse film strength, with the lubricant's ability to cling to gears, bearings, etc....

The film strength of a lubricant is its inherent ability to withstand the effects of load, speed and temperature without breaking down or rupturing, enabling the lubricant to maintain an unbroken film between lubricated surfaces under operating conditions.

In reading about the reduction of ZDDP, I came across an article written by a person who says all oils have the same viscosity once they reach a certain temperature. He went on to talk about some other stuff I felt was not correct and then found out he was basing his theorys on his knowlege of the human vascular system! I will try to find the article again. I think he is a cardiaolgist in Florida that owns a Ferrari and posted this article on some Ferrari Forum. It is entertaining reading.
In response to Grumpy's question about helical gear teeth, since helical gears have a greater contact area, I would suspect you could use a lighter lubricant in the gear drive t-case or anything else for that matter as opposed to straight cut gears.

Hot Damn,school back in.Thanks, I just love learning something new like this.This answers the old question about gear oil or auto trans fluid in a gear transfer.I have heard people argue about that for years.I understand that some oil refiners have started putting in less additives. Have heard that there is less antiwear additives now in Shell Rotella, than before.::(

Yes supposedly it is down to 1200, but I forget the original number as for as the zddp number. All of us with old cars that have flat tappet cams need to keep on top of this! Kind of a hijack, sorry.