As you probably know, brake pads are one of the most critical operational and safety parts of any vehicle, and their uniform thickness is a major factor in how they operate. When your car is not braking as well as it used to and you check the pads, you notice that the wear is not even.
Why do brake pads wear unevenly, and how do you fix them? Brake pads wear unevenly for several reasons:
- rotor damage that puts uneven pressure on the pads
- seized guide pins that do not allow the pads to retract
- a brake line that won’t allow fluid to flow back and forth
- problem with the master cylinder pumping fluid
- a leaking or sticking caliper.
Most of this work you can do at home if you have essential tools and an understanding of how the braking system operates, so let’s look at the possible problems and their solutions.
Wearing Down
Brake pads function by friction. This friction occurs when your caliper pushes the pads against the rotor. This rotor is a fast-moving metal disk with thousands of pounds pushing behind it. When you see the size of the brake pads, a couple of inches wide 4-6 inches long on average, it’s impressive to see how much they do!
It’s normal for front and rear brakes to wear at different speeds from one another because your front brakes take more force from the moving vehicle. However, if there is uneven wear from the left side to the right, you have a problem. There’s a lot to know to look for, so we’ll start at the basics.
Start Stopping Safely
First, if you’re working on your vehicle, always keep safety in mind when working on or inspecting it! One piece of equipment failing could be the difference between a productive day playing mechanic and a trip to the emergency room.
- Turn your vehicle off and remove the keys
- Engage your emergency brake
- Put blocks or wheel chocks behind your rear tires
- Never rely on just a jack to lift your vehicle during maintenance! Always use jack stands.
- It’s also a good idea to have someone around in case something goes wrong. If nothing else, that person can drive you to the parts store (since you can’t use yours) when you realize you forgot something!
- Have the supplies on hand to bleed your brake lines of air. Bleeding brakes is incredibly important because even a little bit of air in your brake lines can severely impact your braking.
Inspecting the Pads
To check your brake pads, loosen the caliper bolts and remove it from its mount around the rotor. Carefully slide the brake pads from the caliper, setting them down in the same direction they were mounted.
If the individual brake pads show uneven wear at an angle (a wedge shape, or a taper along the length of the pad), you likely have a problem with your guide pins or improperly installed pads.
If the outer pad shows more wear than the inner pad, you have a problem with your guide pins.
If your inner pad has the most wear, the problem is with your caliper, brake line, or master cylinder.
Let’s look at each of these components and what it takes to repair them.
Possible Failure #1: Guide Pins
Guide pins fit inside of a rubber bushing to protect the parts and grease from debris and moisture. Over time the bushings can separate, or the grease can leak out. Either one of these will cause the pins to rub on bare metal and become damaged or stuck with friction.
Guide pins are the easiest problem to fix. The grease and pins are cheap, readily available at auto parts stores, and easy to replace.
Remove the pins, clean them, and inspect them for any signs of scratches or gouges. If they show signs of damage, replace them. If they look good but lack grease, liberally apply the lubricant and reinstall them with the bushing.
Possible Failure #2: Calipers
Caliper issues are one of the top causes of uneven wear for brake pads. When a caliper fails to engage properly, it is either not getting pressure to the piston or not releasing it. With the problem of uneven wear, it’s not releasing the pressure.
The Piston is being pushed out, but won’t go back in. Either of those means that your seal or piston is damaged, or the piston has corrosion that has caused it to bind against the internal cylinder.
For this problem, you can hone the cylinder, clean or replace the piston, and replace the seal. This process is called rebuilding the caliper, and it can be an inexpensive way to fix your uneven brake wear. However, that can be time-consuming without the proper tools or knowledge.
The easier route, though sometimes more expensive, is to replace the caliper completely. Usually, you will save a little money on your new brake caliper if you bring the old caliper back to the parts store for a core charge.
Possible Failure #3: Rotors
Your rotors are the disk that your brake pads press against. They are more exposed to the elements and are subject to damage from debris or heat. They should be an even thickness on both sides of the vehicle, just like the pads.
Debris can get lodged between your rotor and brake pads, causing deep grooves to cut into them. The intense heat and rapid cooling of rotors can also cause them to warp, creating an uneven surface for the brake pads to press against.
These are simple to replace since you have already removed your caliper. Remove the old rotors, clean the new rotors with brake cleaner, and slide them into place.
Possible Failure #4: Brake Lines
Brake lines start in the system as metal tubes then become flexible hoses. Both can become clogged or damaged, causing uneven wear to your brake pads.
With the lines removed from the caliper and put inside of a container, you can depress the brake pedal and watch the fluid. If the brake fluid comes out with just a trickle as the pedal is pushed, remove the hose from the metal line and do the same thing again. Doing this will tell you if it is just the hose or the line.
If it is the metal line, this may not be an easy task. Many metal brake lines come with their bends already in them, causing you to need to feed them through tight spaces. If they do not, you need a special tool to make the bends and some skills to go along with it.
This task is better left to trained mechanics in most cases.
Possible Failure #5: Master Cylinder
The master cylinder is the heart of the brake system. This box controls the valves and pressure that supply the system with the brake fluid.
Master cylinders can be replaced at home, but unless you do this regularly, it can be a day-long job. Also, mistakes made while installing can cause problems with your entire brake system. Make sure you study this procedure before you undertake it. Here’s a video that you watch to give you an overview
Time to Stop
As you can see, there are many reasons why brake pads wear unevenly and many things you can do to fix it yourself. Remember that these parts are always moving and working under extreme stress. Regular inspections are essential for these parts not only to save money but to save the life of your car as well as its most important cargo–you and your passengers.