Lipped Brake Discs: Causes & Fixes

Brake discs, also known as brake rotors, are a critical component of your vehicle's braking system. They work in conjunction with brake pads to slow down or stop your car. Over time and with regular use, it's common for brake discs to develop a 'lip' or a raised edge around their circumference. This phenomenon, while often a sign of wear, can also be influenced by various factors and, if left unaddressed, can impact braking performance and safety. Understanding the causes and knowing how to fix lipped brake discs is essential for any car owner who wants to maintain their vehicle in optimal condition.

What Exactly is a 'Lipped' Brake Disc?

A lipped brake disc refers to the condition where a raised, rounded edge forms around the outer circumference of the braking surface. This lip is essentially an accumulation of brake pad material and metal that has been worn away from the main braking surface. It's a visual indicator that the disc has experienced significant wear. The lip can vary in size, from a slight ridge to a substantial overhang, depending on the driving conditions and the lifespan of the disc.

Why Do Brake Discs Develop Lips?

Several factors contribute to the formation of lips on brake discs:

• Normal Wear and Tear: This is the most common reason. Every time you apply the brakes, a small amount of material is transferred from the brake pad to the disc, and vice versa. Over thousands of braking cycles, this gradual process leads to the wear of the disc surface and the eventual formation of a lip. The friction generated during braking causes this material displacement.
• Brake Pad Material: The composition of your brake pads plays a significant role. Some brake pad materials are more abrasive than others. Harder, more aggressive pad compounds can accelerate disc wear and contribute to lip formation more quickly. Conversely, softer pads might wear out faster themselves but be gentler on the discs.
• Driving Habits: Aggressive driving, frequent hard braking, and prolonged periods of riding the brakes (keeping your foot on the brake pedal when not necessary) can significantly increase the heat and friction, accelerating disc wear and lip development. City driving with frequent stops and starts is generally harder on brake discs than steady highway cruising.
• Brake Pad Irregularities: If brake pads are worn unevenly or have hardened spots, they can apply uneven pressure to the disc, leading to uneven wear and the formation of a lip in specific areas.
• Disc Material and Quality: The quality of the brake disc material itself can influence its susceptibility to wear and lip formation. Cheaper, lower-quality discs may not be as durable and could develop lips sooner.
• Corrosion and Contamination: Rust and debris trapped between the brake pad and disc can cause premature wear and contribute to uneven surfaces, potentially leading to lip formation. This is particularly common in areas with high humidity or where road salt is used.

Can You Fix a Lipped Brake Disc?

The answer to whether you can 'fix' a lipped brake disc depends on the severity of the lip and the remaining thickness of the disc. There are two primary approaches:

1. Machining/Skimming the Brake Discs

Machining, often referred to as skimming or resurfacing, is a process where a thin layer of material is removed from the braking surface of the disc using a specialized lathe. This process aims to:

• Remove the lip and create a smooth, uniform braking surface.
• Eliminate minor glazing or hardening of the disc surface.
• Restore the disc to its optimal thickness for effective braking.

When is Machining Suitable?

Machining is a viable option if:

• The lip is relatively minor.
• The brake disc still has sufficient thickness remaining, above the manufacturer's minimum thickness specification. This is crucial for safety and structural integrity.
• There are no significant cracks, scoring, or warping of the disc.

The Machining Process:

This is a job for a professional mechanic. The wheel is removed, the brake caliper is detached, and the brake disc is mounted onto a brake lathe. The lathe precisely shaves off a thin layer of metal until the braking surface is perfectly flat and the lip is eliminated. The disc is then reassembled with new brake pads, which is highly recommended as old pads may be glazed or worn to the old disc profile.

Pros of Machining:

• More cost-effective than replacing discs.
• Reduces waste by reusing the existing disc.
• Can restore braking performance.

Cons of Machining:

• Not suitable for severely lipped or worn discs.
• Reduces the overall thickness of the disc, potentially shortening its lifespan.
• Requires specialized equipment and expertise.

2. Replacing the Brake Discs

If the brake discs are too worn, have developed significant lips, or have other damage such as deep scoring, cracks, or warping, replacement is the only safe and effective solution. This is also the recommended course of action if the disc thickness is already close to or below the minimum specified by the manufacturer.

When is Replacement Necessary?

You should replace your brake discs if:

• The lip is substantial, and machining would take the disc below its minimum thickness.
• The discs show signs of deep grooving, scoring, or cracking.
• The discs are warped, leading to a pulsing sensation through the brake pedal.
• You've already had the discs machined multiple times.
• You want the best possible braking performance and longevity.

The Replacement Process:

Similar to machining, this is best left to professionals. The process involves removing the wheel, caliper, and often the brake pads. The old discs are unbolted and removed, and new discs are fitted. It's crucial to fit new brake pads at the same time as new discs, as old pads may not bed in correctly with the new, smooth surface, compromising braking performance. After installation, a bedding-in procedure is required for both new pads and discs to ensure optimal performance.

Pros of Replacement:

• Ensures maximum braking performance and safety.
• Restores the braking system to its original condition.
• Provides a longer service life for the new components.

Cons of Replacement:

• More expensive than machining.
• Generates more waste.

Checking Brake Disc Thickness

A critical aspect of assessing brake disc condition is measuring their thickness. Every brake disc has a minimum thickness specification, usually stamped on the edge of the disc or found in the vehicle's service manual. A mechanic will use a specialized tool called a micrometer to accurately measure the thickness at several points around the disc's braking surface. If any measurement falls below the minimum specification, the disc must be replaced.

Impact on Braking Performance

A lipped brake disc can have several negative impacts on your car's braking performance:

• Reduced Braking Efficiency: The lip reduces the contact area between the brake pad and the disc, meaning less friction is generated. This can lead to longer stopping distances, especially in emergency situations.
• Increased Braking Noise: The lip can cause the brake pads to 'jump' over the edge, resulting in increased noise, such as squealing or grinding, during braking.
• Brake Judder: While often associated with warped discs, severe lips can also contribute to uneven braking forces, potentially causing a pulsing sensation in the brake pedal or steering wheel.
• Premature Wear of New Pads: If new brake pads are fitted to lipped discs, they will wear unevenly and prematurely as they try to conform to the disc's uneven surface.

Preventative Measures

While some wear is inevitable, you can take steps to minimise the formation of severe lips and prolong the life of your brake discs:

• Smooth Driving: Avoid aggressive acceleration and harsh braking whenever possible. Anticipate stops and allow your vehicle to coast to a halt when safe to do so.
• Regular Inspections: Have your brakes inspected regularly as part of your vehicle's routine maintenance. This allows for early detection of wear and potential issues.
• Use Quality Components: When replacing brake pads or discs, opt for reputable brands and quality components.
• Cleanliness: While difficult for the average driver, ensuring brake components are kept relatively clean from excessive dirt and road grime can help.
• Bed-in New Pads/Discs Correctly: Always follow the manufacturer's recommended bedding-in procedure for new brake pads and discs to ensure they wear in evenly.

Frequently Asked Questions (FAQs)

Q1: Can I drive with lipped brake discs?

A: It is not recommended to drive with significantly lipped brake discs. While your car will still brake, the performance will be compromised, and it can lead to further damage and potentially unsafe braking.

Q2: How often should brake discs be checked?

A: Brake discs should ideally be checked during every routine service or at least once a year. If you notice any changes in braking performance, such as noise, judder, or reduced stopping power, you should have them inspected immediately.

Q3: How long do brake discs typically last?

A: The lifespan of brake discs varies greatly depending on driving style, vehicle type, and the quality of the discs and pads. They can last anywhere from 30,000 to 80,000 miles or more. Regular checks are more important than a fixed mileage.

Q4: Is it better to machine or replace brake discs?

A: It's better to replace them if the discs are significantly worn, below minimum thickness, cracked, or warped. Machining is a cost-effective option for minor wear and if there's sufficient material remaining.

Q5: What is the 'bedding-in' process?

A: Bedding-in is a process of carefully applying the brakes multiple times, usually at moderate speeds, to allow new brake pads and discs to mate properly and achieve optimal friction. This ensures even wear and maximum braking performance.

Conclusion

Lipped brake discs are a common symptom of wear that should not be ignored. While minor lips can sometimes be rectified by machining, it's crucial to assess the disc's remaining thickness and overall condition. In many cases, especially with significant wear, replacing the brake discs and pads is the safest and most effective solution to restore your vehicle's braking performance and ensure your safety on the road. Regular maintenance and inspection are key to identifying and addressing these issues before they become serious problems.