Years ago I would routinely rebuild brake calipers. Caliper rebuild kits seemed to approach the cost of purchasing a rebuilt caliper. For decades I would routinely purchase rebuilt calipers and exchange my old caliper as a core.
Over the past few years, I have had rebuilt calipers fail, and I have been less than impressed with the quality of the rebuilds. I have noticed an increase in quality in the past year, but I have also noticed a large price increase with this increase in quality.
With rebuild kits easily and inexpensively available on line, I have gone back to rebuilding my own calipers. Rockauto has both rebuild kits and new pistons for very reasonable prices. This has become more necessary with a drastic reduction in availability of rebuilt calipers. Most of my Saab calipers are no longer available, either as a rebuilt or a new unit.
To rebuild a caliper, I remove it, clean it, wire brush it, remove the piston and let it soak in a bucket of “Evap-O-Rust” for a day or so. If the piston is frozen, often I can coax it out by pumping the brake pedal. To remove a frozen piston on a caliper that is off the vehicle I have used a grease gun threaded in to the hose hole on the caliper.
Once the caliper is clean and rust free, I paint it. For a bare cast iron look, I use a lacquer paint called “Cast Blast.” It looks just like bare cast iron, but it won’t rust.
I have been very lucky with the condition of the bore. It has been years since I have had a bore that was so rusty it wouldn’t clean up with a cylinder hone.
Once the caliper is painted and honed, it is time to reassemble it. If the piston is scratched or rusty, it must be replaced. I use a thin smear of red brake hydraulic grease on the piston and the seal to prevent damage to the new seal. Sometimes the dust boot can be a bit tricky to install. Most often they are either held in place with a metal ring, or by the piston itself. If held in place with the piston, it needs to be installed before the piston is installed.
The piston should slide in easily. I have a handy tool to push the piston in. I lube the slides and the pins with synthetic caliper lube. Always replace the rubber hose, and use a little never seize on the bleeder screw and the hose threads.