Today we are talking about brakes, more specifically, how you can rebuild/restore them for a few dollars and some hard work. We will be focused on disc brake setups, as they are the most common type on cars today. While disc and caliper brakes come in many sizes and configurations, the basic principle remains the same across the board. A disc, known as a rotor, is squeezed with sacrificial pads by pistons (housed in a part called a caliper) to create friction and produce a stopping force that counters the moving force of the car. There are many aspects to all of these components, rotor type, pad material, fixed calipers vs floating, etc. However we will be looking only at the caliper component of the brake system today. Rotors and pads are wear items typically are just replaced altogether. Calipers on the other hand are quite costly to replace, and often will last the life of the car, provided the seals are kept in good working order.
Brake calipers can vary drastically across manufacturers and platforms however they generally consist of a housing, a bracket and a single or multiple pistons. Floating calipers (typical on your average car) feature a separate housing or body that “floats” on guide pins that attach to the caliper bracket. Higher performance cars feature fixed caliper designs that do away with the guide pins and have brackets integrated into the caliper housing. In both cases these caliper types feature piston(s) that are comprised of a highly refined metal cylinder and a rubber seal around the perimeter of said cylinder. (There are also typically rubber dust boots that help keep the internal seal from degrading, but this is not found on all calipers) The basic idea behind servicing a caliper is replacing all the worn out rubber seals and dust boots if applicable. This is a job best done off the car, as it requires a lot of detailed work.
Once the calipers have been removed from the car, tear down can begin. In our case, we will be rebuilding a set of HP2 S4 calipers. They are a floating caliper design that have two pistons in the housing. The floating design means that the caliper squeezes the rotor from both sides, but only with the pistons on one side. (Floating calipers are more common due the cost savings and simpler designs) We start easy with a simple clean and then removal of all the various bolts holding the caliper together. We started by taking off the delicate hard lines for the brake fluid connections, with that out of the way, we turned our attention to the big stuff. Before we could get to the pistons, we had to split the caliper in half, taking the bracket off and freeing the housing. With the housing separated, we now could remove the second part of the floating slide, which rides the guide pins. This left us with a free housing and two pistons. As you can see the caliper was still very dirty, and had years’ worth of road grime built up. So before attacking the pistons we gave the parts another good bath.
Removing the pistons safely is probably the hardest part of the entire job. We started by pulling off the old torn dust boots and trashing them. This left the piston exposed, however it’s very important that the piston remains unmarred, as the entire brake system depends on the seal between the housing and the piston. To safely remove the pistons we used compressed air. (DO NOT USE MORE THEN A FEW PSI, IF YOU USE FULL PRESSURE, THE PISTONS CAN SHOOT OUT VIOLENTLY AND CAUSE HARM) We started off with a small amount and increased the pressure very slowly until the pistons were pressed out. We also had a nice soft cardboard box for the pistons to fall into, preventing them from being damaged in the process. With multiple pistons the air method can be used but needs to be done with extreme care. Air, unlike brake fluid is compressible and can build up to dangerous levels. Using fluid to extract the pistons is the preferred method, but is also not as easy to do without special tools.
With the housings now fully disassembled, we went to town clean them and the other parts. We used a heavy degreaser and wire wheel to strip most of the dirt away. Once we had gotten the heavy stuff off, we sand blasted the parts in preparation for a new coat of paint.
With the parts masked off, we began the paint process, many thin layers of color until a nice uniform coat of paint had been built up. We used a high heat brake paint that was specifically designed for use on calipers. We found it easiest to use thin wire to hang the parts, which gave us the most access to all the nooks and crannies. With the paint left to cure for several days we began the reassembly process.
We loosely reassembled everything, following the reverse of our tear down. This was a test fit to make sure we had all the parts and everything was in working order. Once we had confirmed it was all good to go we went about reinstalling the pistons. This can be a challenge because with new rubber seals will have a tighter tolerance then the worn ones that were removed. To help us, we used a small amount of brake fluid which acts as a lubricant and helps condition the seals. We also presoaked the seals as well. With the rubber seals in place, we slowly and carefully pushed the pistons back into their housing. Before sliding them all the way in, we reattached the dust boots and slid them into the place. This was much easier with an extra set of hands, so get a buddy to help during this process. With the boots and seal installed, we began the final assembly, making sure to tighten all the parts down to their required spec. After that it’s a simple job of reattaching them to the car.