The unglamorous drive axle—don't ignore it

The unglamorous drive axle—don’t ignore it

Drive axles are the silent heroes in a truck’s powertrain, but due to their position at the back of the truck, the drive axles remain more or less out of view and out of mind. Sharp looking custom wheels may be the only reason the drive axle gets so much as a glance from anyone other than the service technician.

Granted, drive axles are visible, just not very exciting to look at. All the interesting stuff is going on inside the axle. Power comes into the axle after it leaves the engine, passes through the clutch and transmission, flows through the driveshaft and arrives at the axle pinion shaft. The power transfers from the pinion gear to the ring gear where it changes direction to flow right and left to the wheels at a different ratio than when it entered the axle.

The pinion and ring gears where this transition of ratio and direction takes place mate up to one another through some amazingly complex geometry in the gear tooth machining. The tolerances between these gears demand accuracy for proper operation. If the tolerances are not within specifications, as identified in the service information, then the gears can make excessive noise. Noise in the differential is vibration and that can lead to improper wear, overheating, and shortened component life.

While there is a lot of precision needed to initially set up the pinion and ring gears, along with the supporting bearings, there is typically not much effort needed to keep the axle trouble free for many miles. Nevertheless, critical maintenance does need to take place on a periodic basis.

While axles may have additional maintenance points, there are a few general guidelines that work with most axles.

The first point in maintaining an axle is to check for any lubricant leakage and repair as needed.

Second, make sure the proper lubricant is used to fill the axle and that the fluid level is properly set. See your truck service information like TruckSeries from Mitchell 1 for fluid specifications and correct levels.

Third, when checking the fluid level, inspect the fluid for discoloration caused by any water that may have entered the axle. In addition, check the fluid for any metallic residue that has mixed into the fluid from failing gear surfaces or bearings. If there is any indication of water having entered the axle, inspect the axle vent to ensure it is located securely and operating properly.

Fourth, inspect mounting hardware and brackets attached to the axle. This inspection can also include any suspension components. Inspecting these peripheral components can also be helpful in identifying axle gear related noise that radiates into the cab. Gears and tires always make some noise but those noises can be amplified all out of proportion through grounded components that are meant to be isolated through mounts and cushions.

Drive axles may not be the most glamorous part of the truck but they are vital to keeping the truck moving down the road. Taking the simple steps to ensure axles are properly maintained help to keep this system operating smoothly and efficiently.

Additional tips for repair and maintenance of Class 4-8 trucks may be found in the Mitchell 1 ShopConnection Truck blog.

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