When it's time to work on overhauling or restoring your brakes on your classic car, find where they're boxed-up and get ready for serious, dirty effort. So what comes first?
Glad you asked. When brakes for many old cars were manufactured, using asbestos on brake shoes was the norm. Now, it is understood asbestos dust often created by automotive brakes are harmful, and you want to avoid coming in contact with it. As you take apart brake assemblies, be sure to go in with a vacuum at every opportunity to clean out any asbestos dust that may have collected. Consider wearing a dust mask until you're sure that everything has been thoroughly cleaned.
Before starting, though, you want to consider what you're starting with. Do you have drum brakes, either old mechanical or (newer) hydraulic type, or more modern disc brakes? Does your car have a single or dual hydraulic system? Are you planning to add horsepower or air conditioning? Are suspension changes planned?
All these questions need answers before getting to work, since which parts you save — and which get tossed out — hinge on the decisions. If you are going for a "totally original" car restoration the decision is easy: rebuild what's there. If modifications are in order, especially if you plan to drive the car regularly, now is the time to plan for a brake upgrade (discs, power assist, larger wheels, etc.)
With those decisions behind you the work can begin...
Start with the master cylinder. Before opening it up clean the exterior with mineral spirits, then with soap and water. Dry it off and then remove the cover, pushrod, any seals and bleed screws. Then, following your shop manual, remove the inner piston (or pistons, if a dual cylinder). Clean out the interior of the cylinder with soap and water or alcohol. If it's caked-up with brown sludge, remove it with wooden or plastic items (such as chop sticks) so there's no chance of scratching the walls.
Next, shine a bright light into the cylinder and look for rust, major scratches and pitting. Pitting is the result of oxidation and it leaves the inside surface looking a little like the surface of the Moon. How deeply it is pitted will determine whether the cylinder can be honed out, re-sleeved or thrown away.
Note: Re-sleeving is a process in which the cylinder is precisely reamed out on a milling machine to a specified diameter. Then, a new "sleeve," usually brass or stainless steel, is pressed into the cylinder. This sleeve is finished to the original cylinder diameter and creates a fresh inner surface for the piston and seals. Many shops do this work, charging either by the hour or for the total job.
The ultimate decision will also rest upon how rare your classic car is. If it's a Tucker, V-16 Cadillac, or something equally rare, you will be able to justify the expense of re-sleeving because replacements would be very hard to find. On the other hand, if the cylinder came out of a common car like a Mustang it will probably be much more economical to replace a severely-pitted cylinder.
Most cylinders, fortunately, aren't that badly pitted and can be honed out. Hones are readily available at parts stores and can be chucked into your electric drill. When you're ready to hone, set the spring tension snug against the cylinder walls and squirt some clean brake fluid into the cylinder. Spin the drill at a slow speed, running the honing stones up and down in the cylinder until the pitting/scratches disappear. Don't hone more than that, since you could enlarge the cylinder diameter so much that the piston seals won't prevent leaks.
When you're satisfied with the cylinder wall appearance, wash out the brake fluid with alcohol, leaving no grit. It must be spotless when you're done. Stuff some paper towels into the cylinder to protect the walls.
Turn your attention to the exterior. Wire-brush the outside of the cylinder until the surface is clean and rust-free. Wipe it clean with mineral spirits or alcohol, then wipe with metal-prep (phosphoric acid, used for de-oxidizing the metal, available at auto parts or paint stores). When ready, prime the cylinder and paint it an appropriate color (your choice here, either the original factory paint or whatever you fancy). Powder coating is another option, of course. Make sure you stuff paper towels into the bore and tape off other openings so paint won't get inside. If you're painting it the same color as the wheel cylinders/calipers, wait to do everything at once.
Wheel cylinders are simple devices, although some might be of the "stepped" design; that is, the bore is two different sizes so that less pressure will be directed toward one of the shoes. In either case, clean the cylinders as you did the master, then remove the seal and piston(s).
As with the master cylinder, clean out the bore and hone as necessary, then paint the exterior, taking the precaution to mask off the inside.
There are many designs of disc brake calipers. They can have one, two, three or four individual cylinders, all of which need to be clean and free of pitting. If one cylinder is bad, the whole caliper will have to be replaced or re-sleeved.
Care must be taken when disassembling the calipers, since most are bolted together in two halves. Mixing one caliper's half with another's will frequently result in leakage, as will improper torquing of the bolts that hold them together.
Honing caliper cylinders is done the same as wheel/master cylinders. Keep everything clean.
Note: It pays to get the highest quality rebuilding kits available. This is especially true for disc brake caliper kits, since many caliper designs rely on the resiliency of the rubber seals to properly space the brake pad from the rotor.
When ready to install your new parts, lay everything out on a clean sheet of newspaper, plastic or paper towels. Dirt is the enemy of brake systems, so wash your hands before starting or put on latex gloves.
Rebuilding a cylinder is easy: just install all the parts in the order in which they were removed. Follow your shop manual or the instructions contained in the rebuild kit, and don't forget any small clips, ball bearings and springs. Coat each part in clean brake fluid before installing, but try not to get fluid on the outside of the part. Brake fluid will dissolve most paints.
Everyone has an opinion on this subject, so we will simply cite our experience with both types:
Mineral-based brake fluid has been around for 100 years and works extremely well. Manufacturers still use it, even in ABS systems. Its chief disadvantage is that it is hygroscopic (that is, it absorbs water from the atmosphere). Over time, the water in the fluid creates rust, cylinder wall pitting and eventually deposits so much "mud" in the system that things don't work. It needs to be flushed out and replaced every few years, something most owners neglect.
Silicon fluids were developed in the 1960s. The major advantage of silicon fluid is its absolute resistance to water, making it a "permanent" brake fluid. Its chief disadvantages are a slightly higher viscosity, tendency to "foam-up" during bleeding and refilling, and a high capillary action (its surface tension is lower, allowing it to creep, or spread out, along the walls of the brake components, sometimes causing seepage or leaks.) Most silicon fluid-equipped cars exhibit a softer, "spongy" brake pedal effort.
Some brake systems work well with either fluid and some don't. We've had terrible experiences using silicon fluid in vehicles such as: Jaguar XK 120, Sunbeam Tiger, '66 Corvette. On the other hand, we've seen excellent results in: Jaguar XKE, '65 Mustang, '69 Camaro. In the former we experienced seepage and hard-yet-spongy pedal effort. In the latter the systems worked, although the pedals still feel slightly spongy.
It's our opinion that silicon fluid works best in completely rebuilt brake systems that have near-perfect cylinder walls and are spotlessly clean when filled. Any flaws in the system seem to cause failure or unsatisfactory operation. Also, silicon fluid doesn't seem to do well in brake systems that are undersized for the weight of the vehicle. We don't recommend using it in such situations, nor do we advise flushing out an existing mineral-based system and installing silicon fluid.