Here's why:
* Similar Wear: If one CV axle has failed, the other is likely worn to a similar degree, even if it hasn't completely failed yet. Replacing only one means the other might fail shortly after, requiring you to repeat the labor-intensive job.
* Cost-Effectiveness: The labor cost of replacing a CV axle is often significantly higher than the cost of the part itself. Doing both at once saves on labor costs in the long run.
* Balanced Drive: Having axles of different ages and wear levels can subtly affect the drivetrain balance and potentially lead to premature wear on other components.
The exception would be if you have a very specific reason to believe only one axle is bad (e.g., a visual inspection shows significant damage to only one). However, in most cases, the peace of mind and cost savings associated with replacing both axles simultaneously outweigh the potential cost of replacing just one.
