dust boot - piston - spring cup - *spring* - spring cup - piston - dust boot
Spray the mounting bolts and brake line fittings with WD-40 or similar penetrant before attempting to remove the wheel cylinders. Let it soak so it has time to work. The longer the soaking time, the better the effect.
Brake fluid will start to run out when the fitting is turned off. Have a drip pan or plastic tray ready. To prevent line leakage, cap the end of the line with a suitable plug.
1.Wheel Cylinder Removal
Once the wheel cylinder leaves the car, it's time to disassemble and inspect it. The outer boot is usually easy to pry off, but can tear in the process. The new one should come with the rebuild kit.
Pistons in old wheel cylinders often get stuck. Try spraying compressed air into the line fitting. Make sure to put both ends of the cylinder in the rag or the piston will fly through the garage!
If compressed air doesn't unravel them, hold the cylinder upright, spray with osmotic fluid, and soak overnight
Use a tool to push out the inner piston
2.Wheel Cylinder Inspection
After cleaning with brake parts cleaner, look inside the hole. Use a fingernail in the hole if you can. Smooth hole surfaces with a small amount of pitting can be ground. If the dimple feels deep, the hole surface can only be repaired by re-casing or replacing the wheel cylinder.
3.Wheel Cylinder Honing Tool
The next step is to sand and polish the hole to a fine finish. The purpose of honing is to help the cylinder cup form a good seal with the cylinder bore. There are several ways to do this. The most popular method is to use a cylinder honing tool with a hand-held drill.
4.Hone Wheel Cylinder
Using a variable speed drill at low speed using brake fluid as a lubricant, run the honing tool the full length of the bore in a gradual up and down motion. Lubricate the honing stones with clean brake fluid. Try to make a "cross-hatch" pattern. Run the hone long enough to smooth out the bore, but be careful not to over-hone.
After honing, wipe out the cylinder and clean off the stones. Look inside the cylinders and see if all pits and corrosion are gone. Repeat the honing process until the bore is smooth and free of scratches. When done, wash out the bore with soap and water to remove all traces of the hone grit.
Another way to hone wheel cylinders is by hand, or more accurately, by finger. Wrap a piece of emery cloth around a finger and have at it. Switch from coarse grit to medium grit and then to fine.
（A smooth hole means a tight seal and less chance of leaks.）
Wheel Cylinder Reassembly
Check your rebuild kit and make sure the cup is the same size as the old one. Pour a little clean brake fluid into the container and apply brake fluid to the inside of the hole.
step1: Put the spring in the center of the hole, then place the spring cups on both ends (the flat side facing out). The spring will fit into the groove on the back of the spring cup. Put the piston in the hole and spin it back and forth a few times to coat it. Use the piston to push the rubber cup further into the cylinder.
step2: Install rubber dust boots
Installing rubber boots on metal pistons can be tricky. You can rip off the new rubber with a small screwdriver to try and secure the dust cover around the cylinder lip.
step3:Assembly
First the spring, then spring cups (each side), pistons (each side), dust boots (each side)
A good idea is to use an appropriate-sized socket and slip the dust boot over the width of the piston (see picture below). Once it's installed, twist it back and forth a couple of times to make sure it's seated all the way around.
Now reinstall the bleed screw, with a little anti-seize if you like！
5.Put the wheel cylinder back into the vehicle
Install the rebuilt wheel cylinder to the backplate and hand tighten the mounting bolts to loosen the cylinder. First, hand tighten the brake line fitting into the cylinder, then tighten the mounting bolts, then tighten the fitting.
After completing the above steps you have successfully rebuilt a new wheel cylinder！
TIPS：
Rebuild/replace one or both?
Wheel cylinders should be rebuilt or replaced in pairs. Even if there is only one leak, rebuilding or replacing both sides is recommended. If you find that there is only one rebuildable, you can rebuild one and replace the other with a new cylinder.
Wheel Cylinder Rebuild Kit
If you decide to refurbish your old wheel cylinders, first check to see if a refurbishment kit is available for your year, make and model vehicle. Although once a common auto parts store item, today's tuning kits are often only found online.
Provide online video for your reference