Disclaimer: Doing anything to your brakes can be dangerous if it is not done correctly. If you are not 100% confident in doing this, don't do it. I will not be held responsible for brakes failing.
First thing you will have to do is remove the caliper from the car or use a second set. Follow the beginning of this guide to remove the calipers from your car.
One thing that isn't mentioned in the guide above is to remove the brake line from the caliper, to do this use a 14mm spanner or socket.
What you'll need
Air compressor and blow gun
Block of wood (I used the handle of my rubber mallet)
Rags
Brake fluid
Brake Cleaner
Rebuild kit (MB857840) You will need two of these, one for each caliper
Flat screwdriver
Something plastic or wooden to remove the seal like a zip tie or skewer
2000 grit sandpaper
Step 1. Remove the old retaining ring holding the dust boot in with a flat screwdriver
Step 2. Place a block of wood and some rags in front of the pistons and using your blow gun, blow some air in through the brake line hole.
This will force the pistons out and the rags will soften the blow, you need to make sure one doesn't pop out before the other as it will be impossible to remove the other one without re-inserting the one that popped out.
Be sure to keep your fingers clear of the pistons. (You can also use the old brake pads instead of a block of wood)
Step 3. Once the pistons have been blown out you should be able to remove them by hand. Don't try to use pliers or you may damage the surface. If you are having a bit of trouble removing them, give them a little wiggle and twist.
Step 4. Spray some brake cleaner on the piston and wipe it with a rag to clean off any solidified brake fluid/contaminants. If there is minor pitting on it, you can use some 2000 grit sandpaper to remove it.
If there is major pitting on the piston then you will need to get a replacement.
Step 5. Using a skewer or zip tie, remove the old square seal from the caliper. The reason you don't use a screwdriver or anything metal is because you don't want to scratch the inside of the caliper.
Step 6. Give the inside of the caliper a good clean with some brake cleaner.
Remove any corrosion in the cylinder bore using some 2000 grit sand paper. You won't be able to get it completely clean but as long as it feels smooth it should be good.
Give it another spray with brake cleaner and make sure the seal groove is completely clean.
Step 7. Remove the contents from the rebuild kit. The rebuild kit includes (from top to bottom on the photo)
Square seals, dust boots, dust boot retaining rings, slide pin dust boots and assembly lube. Also, not pictured it includes the little rubber bush for the slide pin.
Step 8. You may want to put on some nitrile gloves for this.
Apply some brake fluid to the cylinder bore and the square seal. I like to pour some brake fluid in the cap and spin the seal around in it.
You should also not stick your fingers into the brake fluid bottle if you plan on using it to top up your cars fluid as you may contaminate it.
Step 9. Install the seal into the caliper, making sure there are no twists in it.
Step 10. Apply some brake fluid to the pistons and stretch the dust boot over.
Repeat the above steps with the second piston.
Step 11. Push the pistons into the caliper. It does require some force and if you can't do it by hand use a G-clamp or piston compressor tool.
Step 12. Using a skewer or dull flat head screwdriver, push the edge of the dust boot into the groove on the caliper.
The dust boot has a lip that sits flush with the groove and you need to make sure it is all the way in. I took a photo showing what it looks like when it isn't seated properly.
Step 13. Insert the new retaining ring, this may be a little tricky but I found the best way is to insert one side and then kind of twist and push it.
Repeat the above steps for the second piston.
Step 14. We are almost done. We just have to push the pistons out with the blow gun one more time to make sure the boots and rings are seated properly. Add a bit more packing in front of the pistons this time as we don't want them popping out all the way.
The other dust boots in the kit are for the slider pins and they go on the caliper bracket.
The tiny bush, goes on one of the slider pins. Just slide it off, wipe off any old grease, apply new grease that was supplied with the rebuild kit and slide the new bush on.
I didn't want your brakes. I have 3 sets of calipers. Was just asking if you wanted me to rebuild them for you.
