Ask the Expert: Transmission Oil Analysis

Transmissions are highly complicated systems for converting and directing power from an engine to a drive train or other end application. They are generally on mobile equipment and contain gear sets as well as torque converters, valves, and clutch and brake sets. Mobile transmissions are generally divided into two types: off-highway and highway. Off-highway includes agricultural equipment, heavy-duty construction equipment, mining equipment, and other mobile equipment often used somewhere apart from on a paved road.

Ask the Expert: Transmission Oil Analysis

Representing one of the largest applications of gear sets in the globe, transmissions are a very huge consumer of oil. In the United States, 160 million gallons of oil was used by transmissions in 2016, representing 7% of the global usage of transmission oils.

Lubricants for transmissions are highly specialized and therefore due care must be taken to make sure that the right lubricant is used. Lubricants for transmissions should lubricate the gear sets as well as aid to cool and clean the transmission’s components. Thus, these lubricants must be relatively flexible as they are lubricating fixed drives, differentials, and hydraulic systems.


Generally, these lubricants have a relatively low viscosity, and have plenty of anti-oxidants for durability, anti-friction modifiers, and additives for reducing the potential formation of varnish. The right lubrication must be matched to the transmission. Some of the more popular lubricants are listed by supplier:

  • Allison - TES
  • Ford - Mercon
  • Caterpillar - TDTO/FDOA
  • General Motors - Dexron

The gear sets in transmissions are generally made from tool steels, and torque converters and clutch bands are usually ceramic for dry clutches and paper-based products for wet clutches.


Why Monitor?


Excessive wear can signify an impending failure and hence must be monitored.


Usually, transmission fluids break down as a result of extreme usage or heat.


Dirt, water, and sand are common contaminants. Specifically, if there is an intercooler, the coolant can sometimes end up in transmission fluids.


Recommended Tests

Ferrous Wear

Wear in transmissions can usually be observed as a metallic "fuzz" on the bottom of the transmission housing. While some amount of wear is common in such a system, trending ferrous wear helps to establish whether abnormal wear is occurring or not.

Glycol Contamination

Measurement of glycol contamination is specifically important if an intercooler is being used by the transmission system. Glycol is an unpleasant contaminant that can make the oil useless thereby damaging the transmission. This contaminant is usually measured with the help of elemental spectroscopy or infrared spectroscopy. Generally, elemental spectroscopy detects the presence of high concentrations of metallo-organic corrosion inhibitors in the glycol coolant, but not native to the oil composition. Normally the coolant is added with potassium, boron, silicon and sodium for inhibiting corrosion.

Particle Count

Apart from ferrous or metal wear, transmission systems can suffer from non-metallic wear due to sand particles and dirt. If filter systems are not monitored, these particles can clog them which can lead to premature failure.

It is recommended to use the MicroLab series for monitoring transmissions. It is unusual that people monitor only transmission oil. A normal use case would be to monitor transmission oil, engine oil, and perhaps hydraulic oil. The MicroLab 42 and 40 are perfect solutions for this kind of applications. The MicroLab 42 adds a ferrous wear monitor for tracking and trending ferrous particles.

Spectro Scientific

This information has been sourced, reviewed and adapted from materials provided by AMETEK Spectro Scientific.

For more information on this source, please visit AMETEK Spectro Scientific.


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