Gearbox Oils in Heavy-Duty On- and Off-Road Vehicles

Authored by: Allan Zieser, STLE, CLS

Gearboxes for heavy-duty trucks face a lot of tougher applications than their cousins in the passenger car motor oil (PCMO) side of the family. They have a lot heavier shock loading on the gearboxes caused by the rough terrain and tremendous weights that are jarring the gears in them. Whether in a manual transmission, gear drive, or differential, heavy-duty trucks put a lot of pressure on the gears that drive them.

Gear oils for differentials in heavy-duty truck axels depend on extreme pressure additives and high-quality base oils to provide the protection that they need to maintain proper operation. In addition to the harsh operating conditions, many of these gearboxes also have smaller oil sumps in them and tend to build up heat faster than standard automotive gear drives.

Oils for manual or automated manual transmissions require heavy-duty gear oils without these EP additives in them to maintain proper operation and prevent internal damage.

The two oil types (EP and Non-EP) are not interchangeable with a few rare exceptions. Be aware that both the EP Gear Oils and the Non-EP Transmission Oils are marketed in 75W-80 and 75W-90 SAE weights. Please do not get them mixed up in your shops as you cannot use the transmission oils in differentials, nor can you use the differential oils in the transmissions.

During the next few weeks, we will be going over gear systems in heavy-duty trucks and equipment as well as the lubricants that they require. Be sure and stay tuned over the next few weeks as we continue our series!