Spectro Scientific Blog

Ask the Expert: Oil Analysis for Transmissions

Posted by Professor Dan on May 01, 2018

truck transmissionTransmissions are very complex systems for converting and directing power from an engine to a drive train or other end use. Transmissions are typically found on mobile equipment and consist not only of gear sets, but also brake and clutch sets, torque converters and valves. Mobile transmissions are typically broken down into two categories - highway and off highway. Off highway consists of mining equipment, heavy-duty construction equipment, agricultural equipment and other mobile equipment typically used somewhere other than on a paved road.




Transmissions represent one of the largest uses of gear sets in the world and are a very large consumer of oil. In 2016, in the United States, transmissions used 160 million gallons of oil. This represented 7% of the worldwide usage of transmission oils.

transmission 3 intro

Lubricants for transmissions are very specialized and careful consideration must be taken to ensure that the correct lubricant is used. Lubricants for transmissions must not only lubricate the gear sets, but they also must help to cool and clean the components in the transmission. For this reason these lubricants must be quite flexible as they are lubricating differentials, fixed drives and hydraulic systems.


transmission 3 oil usage

Typically these lubricants have a fairly low viscosity. They have a lot of anti-friction modifiers, anti-oxidants for long life, and additives to reduce potential varnish formation. The correct lubrication must be matched to the transmission. Some of the more well known lubricants are listed by supplier:

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

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

Why Monitor?


transmission 2 why monitorWear - excessive wear can indicate an impending failure and should be monitored. 

Chemistry - if transmission fluids break down it is often due to excessive heat or usage.

Contamination - common contaminants include water, sand and dirt. Sometimes coolant can end up in transmission fluids, particularly if there is an intercooler present.

Recommended Tests

Ferrous wear - wear in transmissions can often be seen as a metallic "fuzz" on the bottom of the transmission housing. Some wear is normal in such a system, but trending ferrous wear helps to determine if abnormal wear is taking place.

transmission 2 recomended tests

Glycol contamination - measuring glycol contamination is particularly important if the transmission system is using an intercooler. Glycol is a pretty nasty contaminant that can render the oil useless, thus damaging the transmission. Glycol is commonly measured using infrared spectroscopy or elemental spectroscopy. Elemental spectroscopy typically detects the metallo-organic corrosion inhibitors that are present in high concentrations in the glycol coolant, but not native to the oil formulation. Sodium, boron, potassium and silicon are commonly added to coolant for corrosion inhibition.

Particle count - in addition to metal or ferrous wear, transmission systems can suffer from non-metallic wear due to dirt and sand particles. These can clog filter systems if they are not monitored, leading to premature failure.

MicroLab_Operator_SampleBottle_20145rev_Mrg copyWe typically recommend the MicroLab series for monitoring transmissions. It's rare that people monitor only transmission oil. A typical use case would be to monitor engine oil, transmission oil and maybe hydraulic oil. The MicroLab 40 and 42 are ideal solutions for this type of usage. The MicroLab 42 adds a ferrous wear monitor to track and trend ferrous particles.

Topics: Fleets