Brake pad installation

I need to replace one of the rear wheel calipers on a 2000 Mercury Sable Wagon, OHV enine, 97,000 miles. 4 wheel disc brakes. Both rear calipers were replaced less than year/3000 miles ago, so I am not replacing both sides. The replacement caliper is a warranty exchange and matches the existing other side. I know that it goes against anything I have ever heard or read, but, my question is, do I have to replace the pads on the recently installed caliper on the other wheel? What is the theory behind the necessity to replace both wheel pads at the same time? Is it just so that the “older” pads do not get forgotten and go beyond their usefull life? All comments appreciated…

I don’t think you “have” to replace the pads with new, but many mechanics choose to do so. A lot depends on when the pads were last replaced and how much use they have been given. Safest approach is to replace.

I would also think that the pads may still be under warranty if they were installed at the same time as the calipers, so you might be able to get free replacement pads.

So much depends on the condition of the pads that a fully detailed answer is hard to provide. I would inspect the pads, and if they have plenty of lining on them, re-use them. On the other hand, I don’t think pads are all that expensive for your vehicle (price range is $20 for generic organic OEM pad set to $70 for Motorcraft OEM), so installing new, along with verifying rotors are true and in spec would be a logical thing to do.

One potential issue you might have is uneven braking if the pad material is different from the other side. Different pad formulas can have different friction characteristics under differing temperatures. That would be my main concern.

I didn’t realize you could buy just one wheel worth of pads. I’ve always bought an axle’s worth with four pads. Either way, the previous response was probably the best advice, you won’t have the same material on the pads for both wheels on one axle, even if you buy the same brand, there might be slightly different chemical mixes in the batch when they made the pads, so I wouldn’t go cheap on this one.

On front brakes I’d suggest changing all four pads and leaving the new rotors, because the new caliper would not seat the old pad in exactly the same spot as the old caliper did and the two sides (right & left of the car) may not pull evenly until the pads break in again, however on the rear it may not matter.

Do it right and change them. Fifteen more minutes, what’s the big deal??