A Closer Look at Drivetrains and Drivetrain Fluids


The purpose of a vehicle’s drivetrain is to draw energy from the vehicle’s engine to provide the thrust needed to induce motion. Through changes in gear ratio, the drivetrain adapts available torque to tractive force. Drivetrain components commonly found in modern equipment include the following: 


Transmissions provide the ability to change gear ratios and available torque. Transmissions may be manual, giving shift command to the operator, or automatic, shifting according to a variety of variables, such as load and speed.


When a vehicle turns a corner, the outer wheels must travel a greater distance than the inner wheels. The vehicle’s differential acts as a balance arm, allowing the outer wheels to rotate at a higher speed and establishing equilibrium of torques and forces between the outer and inner wheels.


Commonly found on vehicles in which the power unit and drive wheels are on the same end of the vehicle, transaxles are compact transmission/differential combinations.

Transfer Cases

Typically found on four-wheel drive vehicles, transfer cases distribute drive power between the front and rear axles.

Power Converters

Power converters are used to transfer energy to a secondary item often having nothing to do with thrusting the vehicle. Every drivetrain component has unique lubrication requirements, but drivetrain fluids in general must perform many of the same common duties: reduce friction and wear, dissipate heat and prevent rust and corrosion. In addition, they must dissipate shock loading, reduce gear noise and inhibit foaming.

Gear Lubricants

Gear designs vary depending on the requirements for rotation speed, degree of gear reduction and torque loading. Transmissions commonly use spur gears, while hypoid gear designs are usually employed as the main gearing in differentials. Bevel gears are usually found in the planetary portion of differentials and in industrial equipment. Various other designs, such as worm gear, herringbone and helical, are used in heavy-duty and industrial applications. When it comes to gear lubricants, performance and application criteria are set forth by the American Petroleum Institute (API). The U.S. military and many equipment manufacturers have their own separate guidelines, as well. API service classifications range from GL-1 through GL-5, with the number indicating level of service severity. GL-1 is the least severe, and its requirements are normally satisfied with motor oil. GL-2 requirements are met with rust and oxidation inhibited oils. GL-3 through GL-5 require the addition of extreme pressure (EP) additives, with higher GL numbers indicating a higher level of EP additive. The MT-1 classification requires good performance in high-temperature applications. Gear lubricants containing extreme pressure additives are required in severe service applications subject to elevated component loading, high sliding pressures and shock loading. By either providing a sacrificial wear surface or changing surface metallurgy, extreme pressure additives provide extra wear protection when the oil film alone cannot prevent component contact and wear. Because lubricants with extreme pressure additives can actually increase friction and wear at lower loads, they should be used only in applications which require their presence. Viscosity is the most important property of a gear lubricant. As with motor oil, the Society of Automotive Engineers (SAE) developed a viscosity grading system for gear lubricants. The SAE system lists requirements for both single and multi-grade lubricants, but does not differentiate between EP and non-EP fluids. Typical SAE gear lubricant grades include SAE 80, 90, 140, 75W, 80W, 75W-90 and 85W-140. Although the grade numbers are larger than those associated with motor oils, gear lubricants are not necessarily heavier. The two separate grading systems are used to minimize confusion  between motor oil and gear lubes.  

AMSOIL synthetic motor oils and gear lubes are formulated to meet the high-temperature/high-load demands of today’s hard-working transmissions and differentials for extended drain intervals. By dramatically reducing friction and wear and resisting the damaging effects of heat and oxidation, transmission temperatures are reduced by 20ºF to 50ºF, equipment lasts longer and requires fewer repairs and fuel economy improves.

Automatic Transmission Fluids

An automatic transmission acts as an energy transfer media, but instead of shifting at the command of an operator, it shifts automatically based on variables such as speed and load. Found in many different applications, automatic transmissions make use of a hydraulic system and a network of gears and bearings, and their design and lubricant demands vary from application to application. Viscosity requirements for automatic transmission fluids vary with the application. Transmission fluids in automotive applications are usually multi-viscosity, ranging from SAE 0W-20 to 10W-30, and include viscosity index improvers to allow adequate low-temperature performance. Powershift transmission fluids, on the other hand, are often single grade fluids.

ATF Viscosity Characteristics

Product SAE Viscosity

Dexron II & Type F 5W-20

Dexron III, Mercon V & ATF Plus 4 0W-20

Caterpillar Powershift 10W, 30 & 50

Different transmissions have different shifting characteristics, from smooth to aggressive, and call for different fluids. It is important to match transmission fluid with the requirements specified by the transmission manufacturer.

ATF Frictional Characteristics

Product Fluid Characteristic

Chrysler ATF Plus 4               Moderately slippery


Dexron II & III, Mercon V        Slippery


Ford Type F, TO-4                 Grabby

(AMSOIL CT Series & ART)

Transmission manufacturers generally specify service and performance criteria for automatic transmission fluids. The newest classifications are generally backward compatible, meaning they are suitable for use in applications calling for an earlier specification. AMSOIL transmission fluids provide automatic and powershift transmissions with unmatched friction and wear protection over a wider temperature range, avoiding breakdown and maintaining viscosity in temperature extremes. AMSOIL transmission fluids resist thermal and oxidative degradation, ensuring cooler and smoother transmission operation and longer transmission life, while also providing increased fuel economy and extended service life. 

Combination Fluids

Combination fluids are most common in agricultural and construction equipment applications, where the lubricant is shared between such components as the hydraulic system and manual transmission. Because the separate components have different lubrication needs, the lubricant must meet the requirements for each. Service classifications are generally set by equipment manufacturers:

Ford Motor Company M2C-134-D

John Deere Quatrol, J20C, J20D & J14C

Massey Ferguson M1127-B, M1129-A, M1135 & M1141

AMSOIL Synthetic Tractor Hydraulic/Transmission Oil (ATH) meets the above classi.cations and provides unsurpassed protection for modern agricultural, construction and industrial equipment. AMSOIL Hydraulic/Transmission Oil exceeds the performance requirements for virtually every piece of modern machinery and provides exceptional lubrication to reduce wear, resist heat, protect against rust and extend fluid and equipment service life.