1991 BMW 735i Drive Axle Assembly Drain & Refill Cost

If the gears in the differential are making noise while driving, or a slapping noise when going into gear, but no leak is present, the fluid may need to be changed due to age, or incorrect type.

Replacing gear oil is quick and straightforward. The gear oil is drained from the lower drain plug, or by removal of the differential cover. The differential cover, if not already, is removed, and the differential housing will be cleaned and inspected. If no further repairs are needed, the differential cover is installed, and the differential will be filled with the appropriate type and grade of gear oil.

There are many brands and types of gear oil available to consumers. Many manufacturers supply a proprietary type that is designed to meet the specifications of that vehicle. They may also indicate optional recommended brands. These recommendations should be followed to help ensure the longevity of the differential.

If vehicles are used in a method consistent with severe duty, as described by the owner’s manual, the severe duty service schedule should be followed. This will include a shorter interval for changing differential oil. Some FWD and AWD vehicles have front differentials that share the differential fluid with the transmission fluid and these two services are essentially one service.

The experienced DIY'er can handle this job with a set of jack stands and a few basic tools and a small torque wrench. This job requires working underneath a raised vehicle, and extreme caution should be exercised. If the individual completing the repair is not experienced with safely lifting and supporting a vehicle, this job should be left to a professional technician.