Front Jeep Brakes the Basics
Front brakes are something that, sooner or later, will wear out on your Jeep. Usually the fronts go first, and then eventually, the rears will wear too, and need to be changed. Like tires, fan belts, and other parts, they're not meant to last forever. Let's look at some of the parts involved, so when you do need to swap out some brake parts, you'll have a general idea of what to look for, and what's involved. We might as well start with the main part that wears out on a vehicle. The brake pads. The pads themselves get pressed against the brake rotors to bring you to a stop, by friction. (The caliper piston(s) push against the pads, which push against the rotor).
Brake Pads - Brake pads are made from many different materials, but some basic ones are: Asbestos Pads - For health reasons, you would be hard pressed to find any pads with this material anymore, but at one time, brake pads did contain asbestos. Non-Metallic Pads - There are various materials brake manufactures can use, some of them artificial (glass), some of them can be cellulose (think plant material). Sometimes these might be called "organic" pads. These can be some of the less expensive made pads as far as cost, although they typically don't last long. Semi Metallic Pads - Just like the name implies, these pads have a mixture of metals and other synthetic and man made ingredients. These are probably the most common type you will see today, even as OE on many vehicles. These can wear on your rotors faster than a non-metallic pad, but have more stopping ability. Full Metallic Pads - You wont see these too often because they are primarily used in racing. You are literally running metal on metal, so these would be brutal on a brake rotor. Ceramic Pads - These are made from clay / porcelain materials. They do usually have a small amount of metal in them, but it would likely be a softer copper metal. However, these are being phased out for environmental concerns (about copper). Ceramics also don't dissipate heat very well. A car manufacturer will usually determine which type of pad to use, based on a lot of engineering criteria, so even though you have a stock pad, it will most likely be one of the above types, (except for Asbestos). Each type of pad has some positive and negative attributes. A vehicle manufacturer, and their engineers, will take these into consideration when choosing a pad design. A sports car that can do 150 mph would use a different kind of pad compound than say, a minivan. So different vehicles will have different citeria and pads. Physically, you can change from one type of pad to another. Meaning, you may want to change from a metallic pad to a ceramic one, or to an organic one. Sometimes this can change other things, for instance, the feel of the pedal when braking, so you may want to keep that in mind when using something other that what the engineers of the vehicle specify. Brake pads usually need replacing simply because they wear out. When you take a brake pad out of the box, it's thicker than a worn one, which are thin, and hopefully, not worn down to their metal backing. In most cases, you can visually check the thickness of a pad just by taking a wheel off and looking in the caliper. Note that the inside pad doesn't always wear the same as the outer one, so be sure and check them both.
Brake Rotors - The brake rotors (or brake "discs") are the part that your brake pads press against to slow and stop the vehicle. Friction between the pad and rotors does the work. Just like your pads, there are a few different kinds of rotors as well. There are two basic types of rotors, which are: one is a vented rotor, the other is known as a 'hat' rotor. The vented rotor is like two rotor faces connected by a series of ribs. The space between them allows are to flow through for cooling purposes. Most of the time (but not always), these types of rotors incorporate a hub. A machined inner part for races and bearings. In cases like these, the wheel of the vehicle bolts onto the brake rotor itself. When changing out a vented rotor, you need to check the races and bearings for damage or wear. Since the new rotors would include new races, you can normally just replace the bearings and the outer seal if needed. Vented rotors will usually include new wheel studs as well. With all these qualities and extra features, rotors that are vented in this way can cost more than a 'hat' rotor. Most rear wheel drive and 4WD cars and trucks, especially in the USA, have used vented rotors with hubs for decades. But some modern vehicles have changed from that format recently.
The other common rotor, the 'hat' rotor, is usually one thick piece of circular steel, with no hub, and no wheel studs. This rotor literally looks like a 'hat' in many cases. It simply slides over the wheel hub and wheels studs that are already on the vehicle. They are very easy to change out, and don't require any grease, races, or bearings. Note that a 'hat' rotor can also be a vented one, depending on the vehicle
Brake rotors can also have a few different styles, or 'faces". Common stock rotors have a smooth machined surface. It does have a very slight roughness to it, and you will see this with your eyes as a minor swirl type pattern. On a common rotor, there are no other machined features, just a smooth flat finish. "Drilled" rotors are used in performance applications. These types of rotors have holes machine drilled into them, and the patterns can vary. The holes are meant for cooling, but also help dissipate hot gasses from braking, and water if you run into some with your vehicle, such as in the rain. "Slotted" rotors are also usually a performance rotor design as well , and typically do the same thing, help dissipate heat and expel hot gasses and water. These types of rotors have "slots" machines into them, almost like small grooves. The downside to these two is the drilling and machining can weaken the rotors metal some, so over time, it might cause an issue with cracking, but that's usually only in extreme cases. (Note that sometimes a rotor may have both, slots and holes.)
As you can see in some of the images, there are combinations of different types of rotors, from "hats" that are slotted to vented rotors that might be a 'hat' design. But at least now you have an idea of the features and difference rotors can have. Brake rotors wear over time. On a brake rotor, there is a minimum thickness it can be to be used safely. Shops can turn a rotor on a brake lathe machine, to make the surface uniform on both sides. This removes metal material from both sides of the rotor. But there is a minimum measurement of thickness that this can be done, and once you are near that figure, the rotor can no longer be turned. You have to replace the rotor. If you have a rotor with deep gouges in it, for instance, maybe you drove to long on worn out pads, then it may need replacing. Some people mention "warped" rotors, but brake rotors are subjected to great heat temperatures when they are made, much higher than they will see under normal driving conditions, so it would be very difficult to warp a steel rotor. A brake lathe can easily tell you if a rotors is warped in any way.
Brake Calipers - The brake caliper holds the brake pads. It usually 'floats' on some kind of bracket, which is bolted to the vehicle, normally to a spindle (also known as a "knuckle") or some other suspension part. Calipers look like they're fixed, but they slide around, in and out with the pressure from the brake pads (when you're braking). They adapt over time to brake pad wear, and keep themselves adjusted so you get even pressure across the face of the rotor. The "slides" usually get a small amount of grease to allow them to move. There can also be guides, pins, clips, and other small parts that keep everything in place and aligned. Calipers use a piston (or pistons, sometimes as many as four) to apply pressure against the brake pads. The brake system is hydraulic, so when you press the brake pedal, that sends that pressure though the master cylinder and on to the caliper's piston. Which in turn, applies that force to the pads. In some ways, this is a very old system, dating back to the 1940's. It's had many refinements over the years, but the basics are the same. Since the system uses hydraulics, you usually have to bleed the air out of the system anytime you disconnect any part of it. Even if it's just for a few minutes. This is something to think about ahead of time if you go to work on the brakes yourself at home. Calipers can go bad. Often the piston(s) can lock up (or 'freeze') inside the caliper housing. Inside the caliper, where the piston resides, that area can become pitted, or tiny debris or rust may prevent the piston from moving in and out as smoothly as it should. Without that movement, the caliper cannot work properly. Another thing that can happen on some of them is the piston seal can fail, leaking fluid out. That again can result in caliper failure. In the old days, you could take the piston out, clean everything up, and reseal it. You can still do that with a rebuilding kit, but calipers are readily available rebuilt, so it's a toss up on if that's practical or not. It depends on the condition of the caliper, piston, and the exact problem.
Calipers use a multitude of different kinds of hardware. Some help it slide on the brackets, some hold the brake pads in place, and still others might attach the caliper to it's mounting. It's always best to check the hardware anytime when you are changing pads, or working with a caliper. Just one of those small parts can hold up the whole job if it's broke or missing. Here are some examples -
Brake Hoses - The brake hose carries the fluid to the caliper. These are normally made of rubber because they need to move with the front suspension. In performance applications, they can have steel braided material on the outside, and may have a stronger inner lining material. But they will still be flexible. They connect directly to the caliper. Usually with a fitting, clip, or with a (banjo) bolt. If you take one off, you will also commonly see a gasket, traditionally made of copper. The metal copper is used because it's a soft metal, and can be crushed to make the seal. You should always replace the washers with new ones to insure you don't have any leaks later on. (don't confuse a brake hose with a brake line - the line is the metal tube portion before the hose to the caliper, and carries fluid from the master or the proportioning valve to the brake hose). On lifted vehicles, you might need hoses that are longer than stock length, and luckily, there are several companies that offer these hoses. Old brake hoses themselves can go bad for a number or reasons. They might leak after the hose material has become cracked or has a hole in it. Sometimes they can collapse inside, and restrict the brake fluid moving through them. This can cause other problems, such as a caliper not functioning right or locking up. It might also prevent you from properly bleeding the brake system after a repair. Always inspect the hoses before jumping into a front brake job and make sure they are in good working order.
These are the basics of the parts in the front brakes. There are other parts in the brake system, such as the master cylinder, or the brake proportioning valve. Of course the rear brakes, which we'll look at in another article. But this should be enough to get you by, and give you at least an idea of what parts make up front brakes and what to look for. (for those with shoes on the front, we will look at drum brakes more carefully in the next article for rear brakes). As always, be safe when doing any mechanical work on you Jeep. See you on the trails !