52 Transmission Digest to Transmission-Fluid Questions By Wayne Colonna Technical Editor 1. Long life with carefree per- formance is something every transmission-repair facility expects to have with trans- mission fluid. And at one time it was easy and carefree; now we are seeing more and more manufactur- ers requiring specific fluids for their transmissions. Why? In my opinion, this is half mar- keting, half technology. Let me ex- plain: When automatic transmissions started to become common and popular in the late 1940s, many of the deficiencies of earlier fluids (straight mineral oils, mainly engine oil) showed that flu- ids used in automatic transmis- sions had to perform many demanding tasks that were beyond the capabilities of the available oils of the time. The tasks the fluids had to per- form were no small matter. They had to transmit power to the torque converters, while optimally performing in the hydraulic con- trol system for shifting; friction control and energy transmission for bands and clutches; lubrication of hard parts, bearings, bushings and seals; and last, but certainly not least, heat transfer for the re- moval of all this generated heat as the transmission changed speed ratio between the engine and drive wheels. It quickly became evident that ATFs would be the most sophisti- cated and most difficult of all lubri- cants to formulate. General Motors took the lead in 1949, and the first specification for automatic-trans- mission fluid was issued for “Type A” ATF. From 1949 until about 1960, most passenger-car automat- ic transmissions required the use of “Type A” or “Type A, Suffix A” transmission fluid. Ford, however, was not thrilled about specifying a transmission fluid for use in a Ford vehicle that was approved by General Motors! So in 1961, Ford released its fluid specification (M2C33-D) that eventually would evolve into the Ford Type F (1967) and Type G for Europe (1972). The passage of the Endangered Species Act of 1972 changed the di- rection of transmission-fluid devel- opment forever by eliminating the use of sperm-whale oil as an addi- tive for transmission fluids. When a suitable replacement for sperm- whale oil was not readily available, it resulted in immense sums of time and money being spent to re- search, develop and manufacture additive packages that worked as well as the sperm-whale oil. It was this huge R&D cost in new fluid- additive packages that convinced OEMs to release their own specific ATF requirement for their trans- missions, a fluid tested and trade- marked by them. Once this decision to differenti- ate and trademark their own ATF generated unexpected new sales, the collaboration among the OEMs to create a universal fluid specifica- tion for all automatic transmissions took a back seat to corporate iden- tity and profits. The OEMs used this opportunity to make “exclusive-use require- ments” that could now be imposed on the customer and the vehicle- service industry. These specific use requirements were justified by the OEMs in the name of improved protection and claims of “fill for life.” The end result has been a proliferation of ATF fluid types that vary by OEM and are available from them, at inflated prices and limited to the dealerships. Lest I be misunderstood, I feel it is important to note that the fluids specified by the OEMs are tested and designed to meet their specific fluid requirements and will protect the transmissions they are de- signed to be used in. There are transmission fluids that meet or ex- ceed the OEM requirements avail- able today that will work as well as or even better than the OEM-speci- fied fluid. This is another of those situations where knowledge is power from the standpoint of being knowledgeable enough about specific fluid requirements to be able to select the proper ATF to substitute when availability or price is a factor. 2. What is the basic composition of a transmission fluid? In most instances, automatic- transmission fluid consists of 85%- 90% base oil and 10%-15% of a transmission- fluid additive package. Because the Answers Publisher’s Note: An inquiry from one of our readers concerning fluids caused us to contact Technical Editor Wayne Colonna. Since the characteristics of ATFs involve a highly specialized science, Colonna called upon the chemists at Lubegard for help. Pat Burrow heads re- search and development at International Lubricants Inc., parent compa- ny of Lubegard. Burrow certainly is biased toward his company’s aftermarket formulations but has endeavored here to keep the discus- sion as generic and educational as possible. ATF 85-90% Base Oil 10-15% Additive Package

November 2004 53 base oil is the largest component of an ATF, it has a dramatic effect on the performance of the fluid over the life of the transmission. The biggest change in fluids over the past decade has been the unilateral move to base stocks that will im- prove the ability of the transmis- sion fluid to flow at very low temperatures, in great part because of the use of electronic controls. At the same time, retention of high- temperature viscosity is required for maintaining film strength for the operation of continuous-slip torque-converter clutches as well as enhancing pump performance by reducing pressure losses (a problem in high-temp front-wheel- drive applications). The additive packages used to blend ATFs are the most sophisti- cated of all lubricant packages. They require about 15-20 different chemical components that are fine- ly balanced to provide the protec- tion and performance required by the OEM specifications. The exact chemical compounds and amounts used for that additive package are specific to the additive manufacturer. Additive packages have had to change to keep up with the demands of today’s auto- matic transmissions. 3. What is the difference be- tween paraffinic, naphthenic, hy- drotreated and synthetic oils? These oils all have one thing in common: They are, or have been, used as base oil for the formulation of transmission fluids. The viscosi- ty-temperature characteristics of an ATF are dependent on the choice of base oil and on the viscosity- index improver used (viscosity- index improvers reduce the change of viscosity with increasing tem- perature). Base oils are refined – by a number of methods – from crude oil, as pumped from the ground. The type of crude oil used and the method of refinement determine the properties of the base oil. Paraffinic oils, prepared by sol- vent-separation techniques from parafinic crude oil, give good yield of high-viscosity-index stocks con- taining a lot of wax. Paraffinics have good thermal and oxidative stability and good high-tempera- ture viscosity characteristics. Low- temperature dewaxing of paraffinic base oils also is required to achieve the low-temperature flow requirements of ATF. Naphthenic oils derived from naphthenic crude are very avail- able and inexpensive. They yield medium-viscosity-index and low- viscosity-index base oils with very little wax and naturally low pour points. Unfortunately, their poor thermal and oxidative stability coupled with their modest viscosi- ty characteristics rules them out for use in today’s high-performance transmission fluids. Hydro-treated oils are derived from almost any crude oil using an alternative refining process that substitutes deep hydrogen treat- ment for solvent extraction. This process can increase the yield of high-viscosity-index components instead of unwanted low-viscosity- index components. This process also reconstructs cracked waxes into branched paraffins, which offer excellent low-temperature properties. The benefits of hydro-treated base oils are key in formulating current and future quality ATFs. Use of hydro-treated base oils has led to the proliferation of “synthet- ic” transmission fluids that have hit the market in the past few years. The higher costs of these products reflect the higher cost to produce base oils. Synthetic oils are perhaps the least understood of all the base oils currently in use. In the lubricant continues next page

54 Transmission Digest market today, there is no absolute definition of the word “synthetic.” In Europe and the U.S., hydroiso- merized base oils (hydro-treated) are being sold and marketed as “synthetic.” Some engineers and chemists would argue that these base oils are not a true synthetic. For them, the definition of a “syn- thetic” would be a molecule built from simpler substances to give the precise properties required. The most-widely used “synthetic” base oils are the polyalphaolefins (PAOs). Others available include the synthesized esters but in gener- al are expensive and have limited availability. “Synthetic” base oils used for for- mulating ATFs all have viscosities in the range of the lighter high-vis- cosity-index mineral oils. Their vis- cosity indexes and flash points are higher and their pour points are considerably lower. This makes them the best choice for formulat- ing transmission fluids for extreme service in very hot or cold environ- ments. The main disadvantage of “synthetics” is that they are more expensive and, until recently, had somewhat limited availability. To further complicate the whole base-oil scenario, all the base oils mentioned can be mixed together in varying proportions to produce base-oil blends that have “the prop- erties of synthetics” and are sold as “semi-synthetic” ATFs. 4. We hear terms like “coefficient of expansion,” “shear factor,” “vis- cosity,” “thermal stability and durability,” “anti-oxidants,” “fric- tion modifiers,” “esters” or “phos- phates.” Can you define these terms, and do they describe the characteristics found in every vari- ety of transmission fluid? Some of the terms you have mentioned are used to describe ei- ther the properties of the additives or the additives themselves. Let me expand on this and define these terms and several others key to un- derstanding what they are and why they are so important to ATF quali- ty. Coefficient of expansion – Expansion in physics is the in- crease in volume resulting from an increase in temperature. The amount of expansion that any unit of volume undergoes for every 1° rise in temperature is called its “co- efficient of expansion.” That’s why it is well known that you are sup- posed to check the fluid level in an automatic transmission when it is at operating temperature, because the volume of fluid expands as it gets hot. Setting the fluid level when cold could result in overfill- ing the transmission. Shear factor – This is a term that is more rele- vant to measuring the distance a point moves because of shear. For our purposes, shear stability is a more-relevant property to use when describing transmission fluid. The operating viscosity of trans- mission fluid is extremely impor- tant to the function of the automatic transmission, especially critical for the performance in electronically controlled transmissions.  Any loss in operating viscosity below a criti- cal level will reduce long-term durability. (Viscosity is a measure of a fluid’s resistance to flow. It is im- portant to remember that viscosity ratings are always given for a spe- cific temperature. Viscosity will in- crease when the temperature drops and will decrease when the temper- ature rises.) Automatic-transmission lubri- cants experience shear stresses at surfaces inside gear and vane pumps, needle bearings and bush- ings, planetary gear sets, and clutches and bands. This mechani- cal shearing breaks the long-chain polymers and, in time, causes vis- cosity loss. Permanent viscosity loss (PVL) occurs after intense shear stress causes unrecoverable degradation of these long-chain molecules. Temporary viscosity loss (TVL) due to the orientation of the long-chain molecules under less-intense shear stress (operating at elevated tem- peratures will do this) with a return to its previous viscosity value indi- cates that the molecules return to their original shape when the stress (lower temperature) is removed. Fluids that do not experience PVL or TVL are defined as shear stable. Thermal stability and durability – A thermally stable transmission fluid is one that has the ability to withstand temperatures without decomposing. Do not confuse ther- mal stability with oxidation stabili- ty, where oxygen must be present and oxidation is occurring instead of thermal decomposition. The transmission-fluid durability, of course, is seriously affected by the onset of either decomposition or oxidation. Both conditions eventu- ally will result in viscosity loss that will cause failure of the transmis- sion fluid and then, shortly there- after, the transmission. Anti-oxidants – Anti-oxidants are part of the ad- ditive package used to formulate automatic-transmission fluid. Their purpose is to lengthen fluid life, permit high-temperature tolerance and prevent the formation of sludge and varnish. These addi- tives control oxidation by deacti- vating chains that start the oxidation that leads to sludge and varnish. Friction modifiers – Friction modifiers are additives that make the fluid more “slippery” by decreasing the coefficient of stat- ic friction. In other words, the frictional forces between clutches and bands are higher when there is no motion or sliding between the clutches and steels (or band and drum) as lockup occurs. When the clutches and steels (or band and drum) are slid- ing as lockup occurs, this reduces frictional force.