Rebuilding you front calipers is easy and cheaper than buying a remanufactured piece from the auto parts store. Because the Miatas from 90+ without sport or MSM brakes have the same caliper, this DIY covers a lot of different years.
If you price it out, you can completely rebuild both front calipers for far less than one refurbished caliper.
You need to assess what your caliper needs for rebuilding it. Typically, just the seals are all that is needed. One set of seals is usually $5 and less, depending on where you buy them. If you chose, you can also replace the slider pins, pin boots, anti-rattle clips and pad springs. If you find your caliper piston is rusty on the circumference, you may need to replace it. It, too, is available for $12-17.
Tools you need:
14mm wrench
17mm wrench
pick tool or small flat screw driver
gloves
compressed air
air nub/trigger
seals
brake fluid
silicone grease
For my purposes, I am completely restoring a pair of calipers. They were painted red at some point, so I am going to bead blast them and replace all the associated hardware.
I had this pair of fronts sitting in storage for many years. I recently noticed my front right caliper might be dragging a bit, so I decided to rebuild these spares. They were dry, so they are a bit gummy. Yours might not be so bad. I have removed the slider pins and boots from the caliper and drained the fluids:
It's always helpful to keep parts with each other. They have been an assembly for a long time and like each other, so I use plastic bags to organize them and keep fluid from leaking all over:
After disassembly, you need to remove the piston. The best, easiest way is with compressed air. Please use glove and glasses. A little fine mist of remaining brake fluid is likely to shoot out during this process and brake fluid is not a pleasant chemical. I began by placing the caliper in a bench vise:
You want to make sure the bleeder is tight and the banjo bolt is removed, you are going to feed air into the caliper through the banjo bolt hole. (FYI - a banjo bolt is the hollow bolt that attaches the brake line to the caliper.) Find something flat and sturdy to put in the caliper between the piston and the caliper body to act as a backstop. This will prevent the caliper from shooting out of the hole. DO NOT use your hands, the force of the caliper will hurt a bit. You can see a few pieces of flat stock aluminum I used for this (it is sitting on the vise). You only need something about a 1/2"-3/4" thick (13-19mm). you can use cardboard stacked up, a magazine, rolled up newspaper, etc.
Now, with the backstop in place and your finger out of the way, put the air nub in the banjo bolt hole and squeeze the trigger. Here's a video of what happens:
(Thanks, Sonny!)
Remove the piston and outer seal:
(the air nub is one the back of the vise, the outer seal is at the lower right, the piston on the left.)
Now, remove the inner seal with the pick tool or small flat screwdriver:
Now use a towel or clean shop rag to clean the cavity in the caliper. Inspect the piston's outer surface for rust, gouges, scoring, or damage. Insect the piston bore on the caliper for similar damage. If the piston bore is damaged, a hone tool may be needed. It's a cheap tool you can put in a drill to clean and hone the bore. The bore is ~2" (51mm), so you don't need a monster hone. A two prong hone will do. You can clean the caliper with brake fluid, mineral spirits, or brake cleaner.
Next, I'll document how to reassemble it, but first I am sending them out for blasting!
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Originally Posted by Mr.Woolery
