1991 Mercedes-Benz 420SEL Drive Axle Assembly Leak Inspection Cost

Differential cover fluid leaks are commonly repaired in the process of servicing the differentials for factory scheduled maintenance. Wheel seals, differential and transmission output seals, and CV boots fail at a significant rate. Most vehicles will need one or all of these repairs at some point in their serviceable life.

Inspecting for axle leaks is very straightforward, diagnosis only requires simple observation while the vehicle is on a lift. If any leaking or seepage is detected, the seal or boot must be changed.

Replacing a wheel seal requires the differential cover to be removed and axles to be disconnected from the differential. Then the wheels, tires, brake drum or caliper and rotor, and axle must be removed. The seal is pulled, and replaced, and the axle housing can be reassembled. For the pinion seal, the drive shaft must be removed, then the pinion nut must be marked and removed. The seal is replaced, and the pinion nut preload will be set. After both repairs, the differential will be refilled with the appropriate type of gear oil. CV boot replacement or output seal replacement require the wheel and the lower ball joint to be removed to free the CV axle. Then the CV boot or output seals can be replaced, and the CV axle may be installed. If the CV joints are popping while the vehicle is turning, the CV axle should be replaced. Then the ball joint can be installed, and the axle nut can be torqued to specification.

We recommend replacing a leaky axle seal or boot as soon as possible. As time passes, the leak will become larger, and there is a very limited amount of gear oil and axle grease to protect expensive components.

There are many types of differentials on modern vehicles. Some are traditional clutch-type, limited slip differentials, or are electronically controlled, torque-vectoring types. The gear oil used in these differentials will vary by manufacturer, and filling with the wrong type of fluid can cause damage to the expensive differential units, requiring replacement.

Anyone can inspect an axle for leaks. The undercarriage of the vehicle is normally very dry and dusty. When a leak occurs, the oil will create a dark, wet spot. This will enable anyone to locate the leak, and decide whether the mentioned repairs are within their abilities. Only a very experienced DIYer should attempt these repairs, as there are assemblies that require experience, skill, and training to properly service.