#ReplacePartsInPairs

David writes:

Over the last few years, I’ve had work done on my ’99 Ford F-150 at various places near my work. It seems that when a wear item goes (like ball joints), the mechanic wants to replace absolutely everything in the system — tie rods, pitman arm, trailing arm, etc. Or when the left side brake caliper goes bad, they want to replace the right one, too. Or give me all new hoses when I replace my radiator.

The reason the mechanic gives is always, “Well they are the same age, and if the left one is bad, the right one is not far behind.”

This gets really expensive really quick. Is this worth it? Why do mechanics always want to replace everything in the system, if only one part is bad? Is this strategy only to boost profit? Or is there some truth in their reasoning?