Most likely, the caliper is stuck on its support pins and fails to slide on these anymore. (The amount of sliding moton, when the brakes are appplied, is very small.) When the caliper is "frozen" on the pins, one brake pad wears much more than the other, and puts undue side thrust on the rotor. This is a common problem in the "rust belt" where road salt is present (and yes, it can happen over just one winter season). If everything else about the caliper assembly is ok, the fix is to install new pins, bushings, pin seals, and brake pads. Also, lub the pin parts with appropriate grease at assembly.

However, the mechanic may not wish certify the repair job when re-using the caliper assembly (for insurance or liability reasons) depending on his state laws. But re-using the caliper is done regularily when replacing only brake pads.

If the holes in the caliper where the pins pass through are worn oversize, then a new caliper and pins are required. Except in cases of early failure of one caliper, calipers are often replaced in pairs, the logic being that if one caliper has failed, the other one is not far behind. It all depends on the nature of the failure.

If you have shoe brakes at the rear wheels, its a good idea to inpsect these for proper operation of the adjusters, too. Very often, these will be stuck too if the calpers (up front) have stuck. Sometimes, these can be refreshed by cleaning and re-lubing the adjusters. While there, look for any broken or badly corroded springs. Replace as necessary. Also, the parking brake cable should be free to move in its sheath else the adjusters may not work well. Replace the brake cables as ncesssary. (One thing seems to lead to another, hey!)

First, a brake caliper is a device that squeezes the pads from the sides against the rotor. If you think of a "vernier caliper" where you are measuring the thickness of an object from the sides, you get the picture of a motion that the brake caliper reproduces, hydraulicly.

Second, brake calipers do seize and often times parts are available to rebuild them, as well as there are replacement calipers, both new and remanufactured. It comes down to considerations of cost, availability, and a fair profit for the shop doing the work, while limiting potential warranty exposure. As some others have mentioned the parking brake is often part of the rear brake calipers on many cars, and without seeing one, I would expect this is the case on the Mazda. IMO the rear calipers that incorporate the parking brake have been a weak link, and very troublesome poprtion of the brake system on four wheel disc. The movement to systems that use small brake shoes that fit inside the rotors in the rear have been a major improvement, except for the fact that we are seeing these rear shoes delaminate in high road salt areas, but thats a different story. The addition of the parking brake to the rear caliper makes it more difficult to repair in the feild. Plus no regular shop is going to have an acid bath that will allow them to completely remove all of the rust and scale that builds up in the caliper slides. So a tech has to improvise the routine and tools that he/she will use to service that portion of the caliper. Trust me, it's not easy in many circumstances and can take a considerable amount of time and not always produce a satisfactory, if not durable result. So given that single point, a shop/tech has to ask why even bother spending the time attempting a difficult task, where the outcome is not assured? Plus we have not even disscussed the actual servicing of the piston and the e-brake components in the caliper! Combine that with the fact that the "cheaper, faster, etc. attitude also applies to how many shops try to hire techs and you will see this becomes even more complicated.

"It takes less talent, and less time to replace a component than it does to remove a component, rebuild it, and reinstall it" Think about that, less time means of course more time to do more work, as in other cars. Less talent means a less expensive work force. That actually means an over all a cheaper cost of doing business, and to a degree a cheaper form of auto service to the consumer. But this comes at a trade-off to some other consumers who might be better served on an individual basis. Jason, in your position, where you think having the tech repair the caliper would be cheaper for your MIL you are partially correct. But, for a shop to routinely do that level of a repair, they would have to hire a more expensive tech, who quite often would be doing more difficult work, which means he/she would turn fewer labor hours a week. The shop would in fact have to use a much higher labor rate and the net result ultimately would be you would get the caliper rebuilt onsite, but the end cost to your MIL, might be the same, if not higher than the bill as it's presently being quoted! By repairing the caliper, the shop wont be making as large of a profit on the parts either, yet the profit margin per hour that the shop needs must be met or the shop will fail as a business.

If this all seems like doubletalk, I'm not suprised. But the bottom line is, the shop is making the correct call by replacing the calipers instead of repairing them. There are techs out there that can and do rebuild calipers on a fairly regular basis. (Me) It's actually expensive to do it that way in most cases, so it's done more out of necessity. Frankly having looked at this many times and quoting replacing calipers VS repairing them, I can actually make more money repairing them dollar wise for a single job. But since we can normally replace them in a fraction of the time for slightly less gross profit, and have all that extra time to do a different car. It becomes a wise choice that ends up costing my customers less in the long run to routinely replace instead of repair calipers.