Semi-Truck Drivetrain Maintenance 101

In this guide, we’ll break down the primary parts of the drivetrain and explain how regular upkeep can extend their service life and keep your rig rolling smoothly.

Drivetrain Structure and Its Critical Components

Transmission

As the first stop for engine power after combustion, the transmission is in charge of gear management. It adjusts torque based on driving conditions, ensuring that the truck can start from a stop, climb steep grades, and cruise efficiently. Whether your truck uses a manual, automatic, or automated manual transmission, fluid health is essential. Dirty or low transmission fluid leads to overheating, gear slipping, and delayed shifting.

Inspect the fluid condition regularly.
Look for signs of burnt odor or dark coloration.
Replace fluids and filters according to the manufacturer’s service intervals.
For manual transmissions, keep an eye on clutch wear, and don’t overlook signs like gear grinding or difficulty shifting.

Driveshafts

Spanning the distance between the transmission and the differential, driveshafts play a role in torque delivery. These spinning shafts rotate thousands of times per minute and are supported by U-joints and, in longer configurations, center support bearings. Over time, the stress and heat they endure can cause these joints to loosen or fail.

Routine inspection and greasing of U-joints is a must.
Listen for clunking noises during acceleration or deceleration and watch for vibrations at highway speeds—both are indicators of an imbalance or worn components. Any play in the joints is a sign it's time for replacement.

Differentials

The differential is what allows a truck’s wheels to rotate at different speeds, particularly when cornering. In most semi-trucks, the rear differential handles the heavy lifting, especially on tandem axle setups. Whether you're working with an open, limited-slip, or locking differential, gear lubrication is essential.

Check and replace the gear oil at specified intervals. Milky or metal-filled oil is a red flag.
Ensure that the differential housing and axle seals aren’t leaking.
For trucks frequently operating in challenging conditions, consider magnetic drain plugs to catch metallic particles and extend gear life.

Axle Shafts

Running from the differential to the wheel hubs, axle shafts must be strong and straight to endure the force they transmit. These shafts spin at high speeds, making their alignment and balance vital. A damaged or bent axle shaft can cause wheel vibration and compromise overall vehicle stability.

Inspect axle shafts during routine service, especially when dealing with noise, uneven tire wear, or vibrations.
Address bearing wear promptly, as a blown bearing can destroy the shaft and even cause wheel detachment.

Bearings and Races

Bearings reduce friction between moving parts, allowing components like axle shafts to spin freely. They sit inside metal channels called races. Without proper lubrication, these bearings heat up, leading to catastrophic failure. Symptoms of trouble include wheel-end overheating, a metallic screeching noise, or visible grease leakage.

To avoid these issues:

Re-grease bearings regularly using the correct grade of bearing grease.
Replace worn races and use bearing packers during reassembly.
Mechanics should also torque the wheel hub correctly to prevent pre-load damage.

Preventive Maintenance Practices

A good maintenance program doesn’t wait for failure—it anticipates it. For semi-truck drivetrains, a few consistent habits go a long way:

Perform fluid checks and top-offs during every oil change
Include drivetrain inspections in 90-day BIT inspections or PM schedules
Use high-quality synthetic lubricants where applicable
Document all maintenance to establish trends and spot irregular wear early

Small details, like inspecting for corrosion around seals or listening for unfamiliar noises, can signal issues before they cascade into costly repairs.

Common Signs of Drivetrain Trouble

Being aware of symptoms is just as important as performing routine checks. Here are some issues to keep on your radar:

Knocking or clunking sounds during shifts
Excessive vibration at speed
Grease splatter around U-joints
Leaking differential housing
Delay in power delivery from the engine to the wheels

Keep Your Drivetrain Rolling Strong

Maintaining a semi-truck’s drivetrain is not just about preventing breakdowns—it’s about maximizing uptime, efficiency, and safety. From the transmission and driveshafts to the differentials and bearings, every component demands attention. Scheduled servicing, quality lubricants, and attentive inspections form the core of a reliable maintenance routine. Treat your drivetrain with care, and it’ll return the favor mile after mile.

If you require drivetrain maintenance in Marshall, MI, contact B&B Services today!