Rearbrakes2
How to rebuild a brake caliper.
Firstly, brakes are obviously the primary mechanism for slowing your car down to a stop. This guide is intended to show the steps required to rebuild a brake caliper. You should make yourself familiar with how your brakes work and make sure you have the tools and skill to complete the job. If not, don't chance it, and take it to a professional.
Now, lets rebuild a caliper. I've chosen this particular caliper because its the more mechanically complex type of a single piston, with sliding anchor and with an internal handbrake. Its off the rear of a R31 Skyline. Calipers that don't use an internal handbrake (ie front rotors) are quite a bit simpler, so if you can follow this particular guide, you can rebuild just about any type. Multi-piston calipers are also simple, you just need to perform the same steps a couple more times. Here is the caliper in question:
When rebuilding, do one at a time. This is because its easy to have a look at the other completed/untouched caliper if you forget where a particular part goes.
We are presuming here that you have removed the caliper from the vehicle already. This involves unbolting both the fluid input and the main bolts that join the caliper to the chassis.
Once its out, the first step is to separate the sliding anchor from the caliper assembly. The anchor is the part that holds the pads and is bolted to the hub. On this particular caliper that involves removing the two 15mm bolts. Place the caliper mounts in a vice if you are having trouble with the assembly moving when you are trying to remove the bolts. Here are the anchor plate and the caliper separated:
Remove the pads from the anchor assembly and then set everything to one side on a clean area.
Next, rip off the dust seal from the piston. You won't be re-using it, so don't be upset if you damage it. Next you want to remove the piston from the bore. Using a caliper with an integrated handbrake is an advantage here as you can use the handbrake lever as a ratchet to push the piston from the bore. Just go backwards and forwards with it, and the piston will simply pop out. If you can't get it that last couple of millimetres, you can use compressed air in the fluid intake hole. Make sure you cover the piston with a large rag to protect you and the piston. If you don't supress it, the piston will shoot out at Mach 3 and cause a lot of damage. Here is the compressed air being applied to the fluid intake:
Here is the piston bore, its really messy and is typical of what you'd find in a 18 year old car. All this mess is making the caliper more and more ineffective.
Remove the o-ring from the inside of the caliper bore.
Remove the handbrake thread rod by pushing from the outside. Then remove the seal from the outside of the handbrake rod and also the o-ring on the rod itself.
Remove the rubber boots and sliding bolts from the anchor assembly:
Now its time to clean it. Degrease and clean all parts with degreaser and metho and a soft brush. Toothbrush is ideal. Once its all clean, dry the caliper throughly. Its very important to remove any moisture from the internals of the caliper as brake fluid absorbs moisture. Compressed air really helps here. I also gave mine a quick sandblast to remove some stubborn dirt (make sure you mask off any internal openings into the caliper) :
Once dry, mask off any machined surfaced and openings into the caliper. This includes the fluid input, the piston cylinder and the thread rod opening. Give the caliper and the anchors a coat of paint in whatever colour takes your fancy. Make sure you use proper high temperature brake paint, or else it will burn off under hard braking. Except to pay around $12 for a self priming can... you'll only need one can to do around 3 coats.
Wait for it to dry, overnight is good. In the morning you should have a shiny as-new finish:
While it was drying, you would have had plenty of time to inspect the innards of the caliper. For the handbrake mechanism to work properly, the threaded rod acts as a ram to push the piston out further to clamp on the brake rotors. When you release the handbrake the rod turns in the other direction to retract the piston. It all sounds simple so far. However it gets complicated when you start thinking about the self adjusting nature of the mechanism. As the brake pads and rotors wear over time, the distance the rod must push the piston out increases. As the throw of the handbrake lever is constant, the engineers have divised a racheting mechanism inside the piston. You can see it here:
The rachet system works virtually identically to a socket set rachet. It can spin in one direction, but not the other. Over time, repeated handbrake applications will push the rod further and futher out. Clever. To keep it all moving smoothly, there is a thrust bearing between the shaft and the caliper body. Its important to remove and inspect it. Mine was very stiff in operation and probably would have resulted in a dragging handbrake. Here is the cleaned thrust bearing :
Here are the bearings installed back onto the thread shaft, ready for installation back into the caliper :
Time for re-assembly.
Put a new o-ring on the threaded rod and screw the rod all the way into the piston as pictured above. Put a new o-ring into the piston bore as well. Smear a bit of brake fluid on the piston, then press the piston/rod combo into the bore until the end of the rod is flush with the outside caliper body. If you have difficulty, you can use a vice with a long socket pushing against the piston, with the caliper body on the other jaw of the vice. After its pressed in, you should be greeted with something that looks like this :
Put some new boots on the anchor bolts and fit them to the plate. Use some silicon based grease to ensure smooth operation. You can see the boots fitted in the picture above.
Bolt the anchor plate to the caliper body and you are pretty much done!
Don't forget to bleed the caliper properly after re-installation *cough chokky*
--Tensop