Q: I want to replace the entire rear differential on my 93 f150 - not take it apart, just replace the entire differential assembly.

Replacing the differential as a complete assembly is a routine, indeed mundane, repair and so it is possible and quite practical. Insofar as cost effectiveness, the answer depends on exactly what is wrong with your existing differential, if anything. If merely a side bearing is worn, making noise, then it will be less costly, and also much less risky (in comparison to installing a used differential for example), to repair what you have. If your differential has wear throughout though, but the rest of your vehicle is in good condition, it is cost effective (economic) to install a brand new, or commercially rebuilt (by a reputable vendor) differential. The drive shaft exists apart from the differential and is not serviced (re-balanced) unless a fault is suspected. It is always a good idea to have the balance on the drive shaft checked, and adjusted or optimized as needed, but driveshaft re-balancing is a separate issue from replacing the differential. If you want further advice regarding this potential project, and possible assistance with whatever repairs turn out to be actually necessary, please refer to YourMechanic’s service request page. If you have further questions or concerns, do not hesitate to re-contact YourMechanic because we want you to make the most of your repair dollars and help you to get the best possible results.