Brake Pads Not Touching Whole Disc: Fixed
So, you just installed new brake pads and calipers, and found that brake pads are npt touching the whole disc. Problems with brake pads not touching the whole disc can be frustrating and dangerous. You may hear strange noises, notice reduced stopping power or feel unusual vibrations when braking. What’s causing this issue and how to fix it? In this article, we’ll explore the possible causes of uneven brake pad wear and share some tips on how to diagnose and solve this problem.
The most common cause of brake pads not touching the whole disc is worn or warped rotors, which could be triggered by several factors. Age, overheating, uneven braking, or poor maintenance practices can all contribute to rotor damage. Next, check the pads themselves. Are they seated properly? Are they of the correct thickness? Is the material worn down so much that it’s not providing enough friction? Another possible cause of brake pads not contacting the entire rotor is a stuck brake caliper. If the caliper is not functioning correctly, it could cause uneven contact with the disc, reducing braking performance. Furthermore, if the motion of brake piston is not smooth, it will prevent brake pad from contacting the rotor. In addition, if the brake pads are not touching the whole disc after a recent replacement, it may be due to the fact that brake pads are not seated properly. Finally, the air in the brake line can also prevent brake pads not touching the whole disc.
Also Read: Groaning noise when braking at low speed
Table of Contents
Understanding Disc Brakes: Key Components and Mechanics
If you want to learn more about disc brakes, it’s important to understand their various components and how they work together to slow down or stop your vehicle.
Disc brakes consist of the following components:
- Caliper guide pins
- Caliper bracket
- Brake pads
- Brake disc
How Disc Brakes Work
When you apply the brake pedal, brake fluid flows through the brake lines to reach the caliper, where it activates a clamp-like mechanism. The caliper moves and applies pressure to the brake pads, causing them to contact the rotor or disc. The friction generated between the pads and rotor ultimately slows down and stops the vehicle.
Importance of Caliper Bracket and Guide Pins
The caliper bracket is essential for connecting the caliper to the steering knuckle and suspension system. Meanwhile, the caliper guide pins are necessary to ensure that the brake pads contact the rotor equally. These small metal pins allow the caliper assembly to move freely in the correct direction, promoting even wear on the brake pads.
In the below video, you can see how caliper moves along the guide pins:
Understanding Brake Pads
Each wheel has two brake pads that are inserted into the caliper assembly. When pressure is applied to the brake pedal, the pads grip both sides of the rotor, generating friction to slow down or stop the vehicle. The inboard brake pad is located on the inside of the rotor (closest to the vehicle’s center), while the outboard brake pad is located on the outside of the rotor (farthest from the center).
Role of Brake Disc
The brake disc (also known as the rotor) is attached to each wheel and spins along with it. When the brake pedal is pressed, the caliper squeezes the brake pads against the rotor surface, creating friction that ultimately slows down the rotation of the wheel and the vehicle itself.
Hydraulic Action of Brake Caliper
When the brake pedal is depressed, the brake fluid pushes the brake piston. The piston, in turn, presses the inboard brake pad against the rotor. Meanwhile, the brake fluid exerts force in the opposite direction, moving the brake caliper along the caliper pin. Due to this action, the outboard brake pad is also pressed, causing the brake disc to be squeezed between both brake pads and apply stopping power.
Recoiling Of Brake Pads After Brake Pedal Is Released
When you press the brake pedal, the brake fluid in the caliper applies pressure to the brake pad, pushing it against the rotor. At this point, a kind of rubber seal on the brake caliper piston, in the form of a “square edge seal”, is deflected, which helps the piston to move and apply the pressing force.
When the brake pedal is released, however, the pressurized brake fluid is no longer present, causing the seal on the piston to snap back into its original shape. This action pulls the piston back slightly, creating a small gap between the brake pad and the rotor.
The square edge seal on the caliper piston uses this same principle by providing a kind of resistance to rolling over, similar to a square section rubber band that has some resistance to rolling over when turned between fingers. The seal can help create the necessary thousandths of an inch of margin clearance needed to separate the brake pad from the rotor surface when the brake pedal is released.
Note: Keep in mind that the piston seal has the shape of an O-ring, but its cross-section is square.
Brake caliper returns to its original position due to springy rubber boots of the guide pins.
Moreover, the rotor itself is not always perfectly flat and can have a slight “wobble” or runout as it turns with the wheel. This wobble can cause the brake pads to be pushed back slightly from the rotor surface when the brake pedal is released. This is known as recoil.
Once the rotor starts turning again, centrifugal force is used to produce a pocket of air around the rotor, which assists in pushing the brake pads back from the rotor surface.
The presence of dirt and air gaps in the pads can impact this process, which is why keeping lubricated pads and slide pins and removing air gaps is essential for maintaining proper brake pads pressing and retraction.
Causes of Brake Pads Not Touching Whole Disc
Here are the causes of brake pads not touching the whole disc:
1. Sticking Slider Pins
When it comes to braking systems in vehicles, one of the most common issues that drivers encounter is the brake pads not touching the whole disc. One possible cause of this problem is sticking slider pins. These pins play a crucial role in ensuring proper braking, and when they become stuck, they can cause uneven wear and tear on your brake pads.
Slider pins are responsible for allowing the brake caliper to move freely, ensuring that the brake pad is in constant contact with the rotor. When these pins become stuck, the brake pad can get stuck in one position, causing uneven contact and wear on the rotor. This can then result in the bicycle kick-like feel that drivers often experience when applying their brakes.
How to spot?
Several factors can cause slider pins to become stuck. Some of the most common causes include:
- Lack of lubrication: If the slider pins are not lubricated correctly, they can become stuck.
- Corrosion: Corrosion can cause slider pins to become stuck in place.
- Debris: If debris accumulates around the slider pins, they can become stuck. Usually, the sliding pin is stuck because over time brake dust gets into the grease, and hardens it.
How to fix?
If the caliper pin is seized with dust, you need to replace them. First, remove the sliding pin and clean the bore in the caliper bracket using a cleaning solution such as CRC brake cleaner or WD-40. I would recommend these stainless steel bore brushes to clean the bore. Dip a bore brush or a cotton swab in the cleaning solution and gently clean the inside of the hole. Also, clean the sliding pin using brake cleaner. After cleaning the bore, spray WD-40 into it.
Next, lubricate the sliding pin with grease. I would recommend this one. Excessive lubrication can trap air at the tip of the slide pin, causing the caliper/pad assembly to drag on the rotor. As such, always ensure that you use the correct amount of lubricant when applying it to the slide pins.
2. Trash Between Caliper and Mounting Bracket
The brake caliper is the component responsible for engaging the brake pads, applying pressure to the rotor through brake fluid, thus slowing down a vehicle’s wheel during braking.
The mounting bracket, as its name implies, is the component that supports the caliper, which houses the brake pads. It’s typically made of cast iron or steel and is bolted to the vehicle’s suspension. The mounting bracket has retaining clips in which it encloses the brake pads.
The caliper is mounted to the bracket in a way that allows it to slide when brakes are applied. This is essential for the brakes to work.
If there is any debris, gunk, or other trash between the caliper and the mounting bracket, it can act like a barrier and prevent the caliper from sliding all the way to the disc. This keeps the brake pad from making full contact with the disc, meaning that the brakes will not be as effective as they should be.
The brake caliper is in direct contact with the outboard brake pad as I explained in the above section. For the inboard brake pad, the caliper piston is in direct contact. So, if there is any dirt between the caliper and the outboard brake pad, it will not be able to uniformly press the brake pad, due to which the brake pad won’t contact the whole rotor.
How to fix?
You should spray this brake dust cleaner to remove any trash between the caliper and the mounting bracket.
First, you need to make sure that your brakes are cool before you start. Now, take brake dust cleaner and simply spray it on your wheels and brake caliper. Make sure to foam it into where the brake pads are located. After a few minutes of spraying, the brake cleaner will foam and drip all the brake dust out. Then, wash the wheel and brake caliper thoroughly with the garden hose.
3. Wheel Is Misaligned
Misaligned wheels can cause several problems, but one of the most serious is that it can make the brake pads not touch the whole disc. When the wheels of your car are out of alignment, they will not be in the correct position relative to the brake disc. This means that the brake pads will not make contact with the entire brake disc, which can reduce the effectiveness of the brakes.
How to spot?
Several signs can indicate misaligned wheels and issues with the braking system. These include:
- Uneven tire wear
- Vibrations when braking
- Squeaking or grinding noises when braking
- Car pulling to one side when braking
- Steering wheel is not centered while driving straight
To align wheels, you have to find a reputable mechanic who has the tools and expertise to align your car wheels correctly.
The mechanic will use a computerized alignment machine to measure the alignment angles of your car’s wheels. This machine will help detect if any of the angles are out of manufacturer specifications.
Next, the mechanic will make any necessary adjustments to the camber, caster, and toe angles to bring them back within the recommended specifications.
4. Wheel Is Not Properly Tightened
If you have recently replaced parts of your car’s disc brake system, you may have removed the wheel to do so. However, when tightening the lug nuts back onto the wheel, it’s essential to follow the recommended torque requirements. If the lug nuts are too loose, the wheel could wobble, causing the brake disc to become misaligned with the wheel bearing. This misalignment can cause the brake pad to not touch the whole disc and lead to potential safety issues.
In addition to tightening lug nuts to the appropriate torque levels, it’s also crucial to tighten them in a star pattern.
When you tighten the lug nuts in a star pattern, it ensures that the wheel is evenly secured onto the hub. This method ensures that the force is distributed evenly across the wheel, which minimizes the risk of the wheel becoming warped.
If you don’t tighten the lug nuts in a star pattern and instead tighten them in a circular pattern, one side of the wheel may become tighter than the other, leading to an imbalanced
So, tightening the wheel in star pattern will help prevent the wheel from going out of balance and causing the brake disc to warp over time. When the brake disc warps, it won’t make proper contact with the brake pad, reducing the vehicle’s stopping power and overall safety.
5. Loose Caliper and Mounting Bracket
When replacing brake parts, you may have to remove the brake caliper and mounting bracket. The brake caliper is bolted to the sliding pin of the mounting bracket, which in turn is bolted to the steering knuckle. It is essential to tighten these bolts based on their specified torque requirements; otherwise, they may become loose over time, causing potential safety hazards on the road.
If the brake caliper and mounting bracket bolts are loose, it may cause the caliper to not apply enough force to the brake pads, resulting in uneven pressure distribution across the brake disc. As a result, some parts of the brake pad may not make contact with the entire disc, leading to reduced braking effectiveness and safety.
Loose bolts may also cause the mounting bracket to shift, resulting in the brake pads moving out of alignment with the brake disc. When the brake pads are out of alignment with the disc, they won’t make proper contact with it when pressure is applied to the brake pedal.
6. Air In The Brake Line
When a brake pedal is pressed, it transmits the force to the master cylinder, which then sends brake fluid through the brake lines to the calipers or wheel cylinders. The pressure exerted by the brake fluid on the pistons in the calipers or wheel cylinders causes the brake pads or shoes to press against the brake disc, stopping the vehicle.
When brake work is being done, if the brake line is removed from the caliper, air can enter the brake hose. This is because air can get into the brake system when it is open and not properly sealed. This air then has the potential to be compressed and act as a buffer, reducing the amount of hydraulic pressure that is being exerted on the piston.
The issue with air in the brake lines is that air is compressible, while brake fluid is not. This means that when the brake pedal is pressed, the air in the brake lines gets compressed, but the brake fluid does not, resulting in a loss of hydraulic pressure. The loss of hydraulic pressure means that the brake caliper may not fully press against the brake disc, causing the brake pads to only touch a portion of the disc.
The result can lead to a spongy or soft brake pedal, which can make it difficult to control the vehicle when braking. Therefore, it is essential to ensure that when you remove the brake line, you have to bleed the brake line.
How to fix?
After you have done brakes related work, and connected brake line to the brake caliper, it is important to bleed the brake line.
To begin the process, have someone sit in the driver’s seat, and pump the brake pedal slowly, while you gently crack open the bleeder screw until brake fluid comes out. Be sure to have a container such as an empty water bottle nearby to collect any spilled fluid.
As the brake fluid begins to flow out, close the bleeder valve by using a wrench to tighten it, catching any leftover fluid in the container.
Note: Release the brake pedal before the bleeder is closed. That’ll just draw air back into the caliper. You need to close the bleeder first.
7. Brake Pads Are Vibrating Due to Lack Of Grease
Brake pads are a critical component of a car’s braking system, and they work by squeezing against the brake disc or drum to slow down or stop the vehicle. However, brake pads cannot function correctly without proper lubrication in the areas between the pads and other surfaces that they come into contact with. This is particularly important for the three contact points of the brake pads: their leading and trailing edges, and their backing plates.
The ears of the brake pads are seated in retaining clips of the mounting bracket, and the backing plate contacts the brake caliper. If there is not enough lubrication in these contact areas, the brake pads will shudder or vibrate during braking since the lack of lubrication causes the brake pads to not be able to glide back and forth smoothly along the retaining clips of the mounting bracket.
If there is insufficient lubrication between the ears of the brake pads and the retaining clips of the bracket, the brake pads can jam and not glide smoothly. The lack of lubrication causes the brake pads to not slide smoothly along the retaining clips of the mounting bracket, which can cause brake pads not to contact the brake disc completely.
Furthermore, the vibration caused by the brake pads’ friction against the caliper’s backing plate can also cause the brake pads to not make contact with the entire surface of the brake disc, reducing braking performance.
How to fix?
To solve this issue, the brake pads’ contact points must be lubricated using high-temperature brake grease or an anti-seize compound. This helps to reduce friction and wear during braking, as well as reduce vibrations and ensure that the brake pads can glide smoothly along the retaining clips of the mounting bracket.
I would recommend ATE Plastilube Grease. Apply it on the ears brake pads and backing plate. to fight the rust from returning and binding the pads. You should also apply grease on the area of the backing plate of the brake pad where it contacts the brake caliper. Make sure you don’t apply grease to the friction plate of the brake pad as it will damage the material and brake rotor.
8. Improper Size Of Brake Pads
When it comes to a vehicle’s braking system, the size of the brake pads is of utmost importance, and any deviation from the recommended size can cause problems. The most common causes of brake pads not touching the whole disc are the purchase of cheap and improperly-sized aftermarket brake pads and installing rear brake pads on the front wheels, as front brake pads are relatively thicker and longer than rear brake pads.
You will find aftermarket brake pads having the same backplate dimensions, but different friction material dimensions, due to which there will be a bit more unswept area on the inner and outer edge of the disc than normal.
If you buy aftermarket brake pads that are too long, they may not fit in the retaining clips properly and won’t be able to glide smoothly. Grinding off a small amount of material from the pads may help to fit them into the caliper mounting frame correctly, but it’s important to be careful and remove only a small amount of material at a time. Test the pads after each grinding session and repeat the process until they seat in the frame properly.
On the other hand, brake pads that are too short in length may not hold themselves in place by friction and may not glide smoothly along the caliper bracket retaining clips when the brakes are applied. This can cause poor braking performance, and the brake pads may not touch the whole disc.
Furthermore, brake pads that are thinner than the OEM recommendation may create too much space between the brake pads and the caliper. This can make it difficult to apply the brakes during an emergency, and there may not be enough pressure to squeeze the brake pads into the rotor when the brake is not applied. This constant contact between the brake calipers and the brake pads is crucial to the safety and stability of the vehicle.
9. Caliper Piston Is Damaged
The caliper piston is an essential component of the brake system responsible for applying pressure to the brake pads against the rotating disc. When the brake pedal is pressed, the hydraulic fluid is transferred to the caliper, and the piston is extended to press the brake pad against the disc, creating friction that slows down or stops the vehicle.
However, when the caliper piston is damaged, it won’t extend completely, resulting in insufficient pressure to press the brake pads against the whole disc. This can lead to reduced braking performance, increased stopping distance, or brake failure, posing a significant safety hazard.
A damaged caliper piston may be caused by dirt, debris, or corrosion, which can damage the seal inside the piston, making it difficult to extend or retract effectively. This can result in the piston sticking in place or not extending as far as it should, leading to a loss of braking power.
To test for a damaged caliper piston, one can use a big G-clamp to push it back and observe how the piston moves. If there is any binding or inconsistencies in the motion, such as a rough feel or a dragging sensation, it can indicate that the piston may be bad and needs replacement. Sometimes, the entire caliper may need to be rebuilt if the damage is severe.
10. Glazed Brake Pads
if the brake pads are glazed or not wearing flat, it can lead to some areas on the brake disc being unswept.
Glazing occurs when the brake pad material overheats due to heavy or extended use of the brakes. Brake pads have an optimal operating temperature range, and when exceeded, the binders and materials in the pad start to melt and glaze, reducing its ability to slow down the vehicle effectively. This process often results in a grinding noise that is audible when pressing the brake pedal.
Glazed brake pads have a shiny and glossy appearance where they contact the brake rotor, and their surface may also show signs of small cracks. This can lead to uneven and incomplete contact between the brake pads and the disc, leaving some areas untouched.
If the brake pads are lightly glazed, they can be fixed by wetting them with isopropyl alcohol and sanding them with 280 to 320 grit sandpaper on a granite stone or a concrete slab. Scuffing brake pads on concrete sidewalks or asphalt surfaces is another option that reduces the glaze effect and improves brake performance.