Coping with Specialty Fluids for Hydraulic Testing #2: Automatic Transmission Fluids

July 30, 2014 - "Blog"

Tuesday, July 29, 2014

This is the second in a series of articles outlining the system requirements and considerations when using specialty fluids for product test stands.

Automotive Transmission Fluids

Since its introduction, Automatic Transmission Fluid, or ATF, has been in use since the early 1950’s. Through the years, several changes have been introduced, from the use of whale oil as a friction modifier up until the 1970’s, to fluid developed to increase oxidation resistance and anti-wear performance in the mid-1970’s. In the early 1990s, we saw changes to low-temperature viscosity requirements, volatility requirements, viscosity change limits after high temperature exposure, and new improved oxidation limits..Since that time, new fluids have been developed, on what seems to be a yearly basis, to meet the new demands of modern transmission design. With the development of each version come new fluid and components testing and qualifications, creating a steady demand for transmission and control components.
ATF is manufactured by several companies, and product branded under various names such as Ford’s® Mercon®, GM’s® Dexron®, and Allison’s® Heavy Duty ATF to name just a few, and can be easily be identified by its red color. While generally a forgiving fluid to operate on, ATF does present some challenges to the design, operation, and servicing of Servo-Based Hydraulic Test Stands in today’s marketplace.
Health and Safety Requirements
Automatic Transmission Fluids can become an irritant to human tissue after repeated exposure. Gloves and goggles are recommended as a minimum in safety equipment when servicing ATF systems.
Skin Protection
Prolonged or repeated skin contact should be avoided as ATF’s can create an itchy red rash. If left unattended, this could result in complications such as dermatitis or even secondary infection from bacteria. Once the fluid is removed by washing with soap and water, any pain should subside.

Eye Exposure

First aid is recommended by immediately flushing the eyes with large amounts of water or a standard eye irrigation solution. Continued washing with water will usually be enough to remove the fluid and cause the irritation to cease. Secondary treatment should be sought by a medical professional, as possible infections could occur. Always remember to wear safety glasses or chemical goggles to prevent eye exposure when working around all fluids.

Inhalation of ATF Fluids
ATFs have a low vapor pressure and generally do not present an inhalation hazard at ambient temperatures. However, care should be taken to prevent aerosolization or misting of the fluid, especially at higher temperatures.
In all cases, users should review the fluid’s Material Safety Data Sheet (MSDS) and fully understand the effects and treatments required by the specific fluid being used.

System Design Requirements

System design can be a challenge when automatic transmission fluids are utilized. System material, seal composites, and the large swings in fluid viscosities should be taken into account in all aspects of component selection. This includes secondary components such as wire coatings, electrical connectors, grommets, gaskets, and seals.

Component Materials

Since Automatic Transmission Fluids are fairly forgiving, most materials used on standard petroleum hydraulic systems can be utilized in systems. Care should be taken to avoid selecting components with external or internal materials, such as copper or bronze, as some brands can react quite aggressively with these materials.
Seal material selection is critical in hydraulic components. Components utilizing fluorosilicone, fluorocarbon, or polyurethane should never be used, and materials such as neoprene, butyl, and nitriles (Buna-N) should only be used as static seals, if at all. Preferred seals include ethylene propylene, VitonTM, and styrene-butadiene rubber (SBR), but the operational temperatures must always be taken into consideration.


A quality high-temperature epoxy should always be used with ATF. Enamels can peel and turn an odd shade of pink when exposed to the fluid. Generally, most manufacturers who build test systems utilizing ATF fluids will use stainless steel reservoirs and structures to avoid the failure of painted surfaces.

Reservoirs and Conductors
While ATF are not considered hygroscopic, care should be taken when testing from ambient to very high temperatures, as water can form within the fluid. In order to keep moisture in the air from absorbing into the fluid, fluid reservoirs should be designed as sealed systems, or desiccant breathers utilized to absorb moisture from the air. Flat-faced O-Ring fittings seal material must also be changed out to be compatible and avoid potential failures.

Because ATF can degrade quickly at high temperatures, systems also require a rigid preventative maintenance and condition monitoring plan as part of the lab’s regular routine.

Other Requirements

Other areas to consider when using ATF fluids are items normally not taken into account when working with standard hydraulic fluid systems. For example, you must consider compatibility issues related to plastic or coated tools, clothing worn by employees, shoe or boot sole materials, and computers located with the immediate exposure area.
Automatic Transmission Fluids can omit a rather strong smell, especially at higher temperatures. Test stand and plant vapor collection and filtration system should be included when testing. Activated carbon mist collection elements can be used to greatly reduce the orders associated with testing.
Regular fluid testing should also be conducted on a compressed timeline basis. The fluid appearance should be closely monitored along with particle contamination counts. Frequent particle counts and contaminate material make-up can provide an indication of possible component breakdown and immanent failures associated with ATFs..
For more information on hydraulic servo-based test systems for specialty fluids, please contact Wineman Technology for a system audit and recommendations today.
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