How to Fix Disc Brake Pulsing

Experiencing an unnerving pulsation or vibration through your brake lever? Don’t panic – solving disc brake pulsing is doable if you pinpoint the cause and make the right repairs.

We’ll dig into the root causes, explain step-by-step DIY fixes, and provide tips to prevent issues in the future. Whether you’re dealing with a warped rotor, contaminated pads, compatibility problems or other common causes, this guide will take you through the entire process from start to finish.

Here’s a look at what we’ll cover:

• What brake pulsing feels like and what causes it. A proper diagnosis is crucial!
• Progressive solutions for warped rotors – from bedding to replacing.
• How to clean and fix contaminated pads covered in oil or debris.
• Correcting pad and rotor fit issues that lead to vibration.
• Re-aligning the caliper position for smooth, even braking.
• Finding and fixing the inevitable loose parts that cause problems.
• Daily and monthly maintenance to prevent future pulsation issues.

Let’s get started with the basics – what brake pulsing is, what it feels like, and how to recognize the root causes.

Chapter 1 – What is Disc Brake Pulsing and What Causes It?

Before we get into solutions, let’s make sure you understand what brake pulsing is and what causes it.

What Does Brake Pulsing Feel Like?

You’ll feel the pulsing as a rhythmic vibration or pulsing sensation through the brake lever when you apply the brakes. It feels almost like the brakes are grabbing and releasing slightly with each revolution of the wheel.

The pulsing and vibration is usually felt mainly through the brake lever, but can sometimes transfer through the handlebars as well.

Main Causes of Brake Pulsing

There are a few common causes of brake pulsing:

• Warped rotors – Heat from braking can warp the rotor disc shape into slight waves. As these pass through the caliper, they create pulses.
• Pad contamination – Oil, grease, or dirt on the brake pads reduces friction unevenly. This creates high and low friction spots that pulse.
• Bad pad/rotor fit – If pads and rotors aren’t matched well, they can vibrate and pulse.
• Caliper misalignment – If the caliper isn’t perfectly centered on the rotor, this creates an uneven braking surface.
• Loose parts – Anything loose in the brake system – pads, calipers, bolts – can move and cause pulsing.

Understanding the root cause is key before attempting any repairs. Diagnosing the issue takes some investigation, which we’ll cover next.

Chapter 2 – How to Diagnose the Cause of Brake Pulsing

Before fixing your pulsing brake issue, it’s crucial to correctly diagnose the cause first. Getting the diagnosis wrong could lead to wasted time and money on unnecessary new parts.

Here are systematic steps to isolate the root cause of the problem:

Step 1 – Check the Rotor

The first thing to check is the rotor itself. Grab the wheel and try rocking it laterally while looking at spacing between rotor and pads.

• If the rotor wobbles side to side, it could be warped.
• Also check thickness – rotors can wear down over time.

Step 2 – Check Pad and Caliper Alignment

Look at where the pads make contact on the rotor face.

• Pads should sit perfectly flush, centered on the rotor surface.
• Misalignments here can cause pulsing.

While checking this, also confirm pads are the proper width to match the rotor. Mixing incompatible pads and rotors is a common cause of vibration.

Step 3 – Check for Contaminants

Inspect pads and rotors closely for oil, grease or embedded debris. Contaminants reduce braking performance and can create pulses.

• Metallic debris can become embedded in the pad material over time.
• Oil or grease is a sign of leaking hydraulic fluid.

Step 4 – Isolate the Brake

Test the braking force on each wheel individually. If pulsing is isolated to just one wheel, the issue is likely in that brake caliper or rotor.

Step 5 – Check Mounting Hardware

Grab wheels, calipers, adapters and bolts to check for any loose parts. Loose mounting hardware can allow components to move and pulse.

Once you’ve isolated the root cause – warped rotor, contamination, misalignment, etc – you can move forward confidently with the proper repair.

Chapter 3 – Fixing Warped Rotors

Heat from braking forces can warp rotors over time into slight waves. As these pass through the caliper, they create a pulsing sensation.

Replacing warped rotors is the best permanent fix. But there are also a few DIY methods to try rescuing them.

A. Try Bedding In the Rotors

Bedding is the process of mating the pads and rotors together through controlled heat cycling. This can sometimes remove minor warps and smooth things out.

Here is a proper bed-in process:

1. Accelerate to a moderate speed without using brakes at all.
2. Apply brakes moderately to come to a near-stop without locking up wheels.
3. Repeat the accelerate and brake sequence 20-30 times.
4. Allow components to cool completely between cycles.

This controlled heating and cooling can re-set the shape of warped rotors. If a pulse is still felt after bedding, try the next steps.

B. Attempt to Mechanically Straighten the Rotor

You’ll need:

• Wheel removed from bike
• Rubber/plastic mallet
• Rags/gloves to protect rotor

Steps:

1. Spin wheel and watch closely for high spots in rotor as it passes caliper.
2. Place rag or glove over rotor surface to protect it.
3. Lightly tap high spots with mallet to bend rotor straighter.
4. Reinstall wheel and test braking.
5. Repeat steps 1-4 until rotor spins true.

This technique works best on very minor warps. Exercise caution not to bend the rotor too far out of shape.

C. Sand the Rotor to Remove Warps

You’ll need:

• Wheel removed
• Sandpaper – 320 grit and higher
• Clean rags
• Isopropyl alcohol

Steps:

1. Remove wheel from bike. Clean rotor thoroughly with alcohol to degrease.
2. Shake can of isopropyl alcohol spray and mist the rotor surface. This helps identify any existing warps.
3. Place sandpaper on flat surface. Gently slide rotor over it with mild pressure to remove high spots.
4. Wipe clean. Reapply alcohol mist to check flatness.
5. Spin wheel and inspect rotor alignment again. Repeat sanding if needed.
6. Once fully straightened, do a final sanding with 600+ grit sandpaper to smooth surface.

Be cautious removing material – rotors have minimum thickness specs. Measure thickness regularly during this process.

D. Replace the Rotor

If resurfacing methods don’t solve the pulsation, replacement is the only option.

Steps for replacing rotors:

1. Inspect mounting hardware – may need new bolts/washers.
2. Clean caliper mount points thoroughly.
3. Install new rotor, adding threadlocker to fasteners. Torque to spec.
4. Re-seat pads with a few moderate stops. Check alignment.
5. Bed in the new setup properly.

Replacing both rotor AND pads together is wise for optimal braking performance.

Chapter 4 – Fixing Pad Contamination Issues

Oil, grease or debris on the brake pads can cause pulses during braking. This uneven friction leads to vibrations.

Here’s how to clean contaminated pads:

A. Fix Oil or Grease Contamination

• Use dish soap and water to thoroughly degrease the pads.
• Isopropyl alcohol also works well to dissolve oil residue. Wipe down completely.
• Very lightly sand pads with fine grit sandpaper. Be cautious not to over-sand.
• Burnish and bed in the pads properly. Test braking performance.

Significant hydraulic fluid contamination requires replacing pads fully. Don’t risk braking performance.

B. Remove Embedded Debris in Pads

• Use a sharp utility knife to gently lift and pick debris fragments lodged in the pad material.
• Rub gentle pressure across sandpaper to remove small embedded contaminants.
• Pick out larger rocks and pebbles with a utility knife or pick.
• Permanently fix the source of contamination – worn cables, leaking seals, etc.

C. When to Replace Pads

If too much material has been compromised by contaminants, replacement is required.

Signs pads are too far gone:

• 25% of pad friction surface is contaminated.
• Friction material is cracked or damaged.
• Braking performance is still compromised after cleaning.

Tips for replacing contaminated pads:

• Replace pads in complete sets – front or rear. Mixing pads causes issues.
• Clean caliper thoroughly of any contaminating agents.
• Lubricate caliper slider pins, bolts, and mounting hardware.
• Bed in new pads properly with controlled stops.

Fresh brake pads are inexpensive insurance against unsafe braking.

Chapter 5 – Correcting Bad Pad/Rotor Fit

If the brake pads and rotor don’t match properly, pulsing and vibration can occur during braking.

Follow these tips to ensure components match:

Use Original Parts or Cross-Compatible Sets

Mixing and matching pad/rotor sets from different brands often causes issues. Using parts designed specifically to work together prevents problems.

Some tips:

• Stick with rotor and pad sets engineered by your brake manufacturer.
• Research cross-compatibility between brands thoroughly before mixing.
• Closely match any replacements to the stock components.

Ensure Proper Rotor Width

Pads should contact the rotor face evenly across the entire width. Rotor width must match caliper specs:

• Measure rotor width between brake track edges.
• Consult manufacturer specs for proper rotor sizing.
• Incorrect rotor width is a common cause of vibration.

Fit Pads Correctly in the Caliper

The pads must sit snugly in the caliper without side-to-side play:

• Inspect pad retaining clips, anti-rattle hardware, and guiderails. Replace if damaged.
• Lubricate caliper mounting points to prevent binding and uneven pad wear.
• Ensure proper pad spacing adjustment.

Bed In Brakes Properly

Bedding seats the pads and rotor together in the caliper for maximum contact:

• Use light controlled stops to transfer pad material onto rotor face.
• Let components cool between intervals to prevent overheating.
• Bedding helps mate surfaces together smoothly.

Getting pads and rotors aligned and mated properly prevents pulsing issues down the road.

Chapter 6 – Fixing Caliper Alignment Issues

If the brake caliper isn’t perfectly centered on the rotor, only part of the pad makes solid contact. This uneven braking surface causes pulsing.

Here’s how to realign a misaligned caliper:

A. Inspect Mounting Bolts

Grab the caliper body and shake lightly to check for play. Any loose mounting bolts will allow movement.

• Ensure bolts are torqued to spec with threadlocker applied.
• Inspect washers, nuts and bolt heads closely for damage. Replace if compromised.

B. Adjust Pad Centering

Pad adjustment dials fine-tune alignment by moving the pads closer to or further from the rotor:

• Consult manufacturer instructions for proper adjustment procedures.
• Make small incremental turns of the dial for precise adjustments.
• Re-check centering often while tuning.

C. Align the Caliper Manually

If alignment dials don’t solve it, manual realignment is needed.

You’ll need:

• 5mm hex key
• 8mm hex key
• Brake pad spacer tool

Steps:

1. Position spacer tool between pads to press pistons back into caliper.
2. Loosen caliper mounting bolts just enough to allow adjustment movement.
3. Adjust caliper alignment by nudging body while monitoring pad centering.
4. Snug mounting bolts lightly and recheck pad alignment.
5. Once aligned, torque bolts back to spec and reinstall pads.

Take the time to get the caliper perfectly centered for smooth, even braking power.

Chapter 7 – Checking for Loose Parts

Loose mounting hardware anywhere in the braking system can transfer motion into pulsing at the brake lever.

Here’s what to check:

Inspect the Caliper Mount

Grab caliper body and shake gently to check for play:

• Ensure caliper bolts are tightened to spec using a torque wrench.
• Check that rubber grommets or mounting sleeves aren’t torn or damaged.
• Damaged mounting points can allow the caliper to rock and pulse.

Check Hub and Axle Tightness

Use a 6mm hex key to ensure the hub bolts or thru-axle are securely fastened.

Gently rock the tire/wheel laterally to check for any play indicating a loose hub.

Check Adapter Bolts

Many brakes use mounting adapters to fit the rotor size. Adapter bolts must be rock solid.

• Ensure proper torque on all adapter fasteners using a 4 or 5mm hex key.
• No movement should be felt where adapters attach to frame or caliper.

Inspect Rotor Bolts

The rotor must seat perfectly flush against the mounting flange surface:

• Alternately tighten opposing bolts to pull rotor evenly into alignment.
• Use a torque wrench and threadlocker for critical fasteners.

Any wiggle or play allows pulsing vibrations to transfer. Take the extra time to securely fasten all hardware.

Can Disc Brake Pulsing Cause Popping Sounds in My Bike?

Can disc brake pulsing cause popping sounds in my bike? Bike popping sounds: causes and fixes.

Chapter 8 – Maintaining Your Brakes to Prevent Future Pulsing

While repairs may fix brake pulsing now, proper maintenance helps prevent issues from recurring.

Here are some tips:

Keep Rotors and Pads Clean

• Regularly clean rotors with isopropyl alcohol to degrease.
• Brush debris from inside calipers, especially lubricating points.
• Never touch rotors or pads with oily hands.

Check Pad and Rotor Wear

Inspect thickness regularly:

• Pads should be replaced when reaching the minimum thickness spec.
• Measure rotors at regular service intervals. Machine or replace when worn.

Worn braking surfaces vibrate and pulse more readily under heat and force.

Lubricate Calipers

• Caliper sliders and mounting points should move freely and smoothly.
• Lubricate with high quality brake grease only.

Sticky pistons increase pad wear and contribute to uneven friction.

Bed in New Components

• Always bed in new pads and rotors properly with controlled stops.
• This mates surfaces together smoothly.

Follow these tips and your brakes will stop smoothly for many miles down the road!

Conclusion

Brake pulsing is common, but solving it is doable after identifying the root cause accurately. Take the time to properly diagnose and correct issues for safety and performance.

Follow the step-by-step guides covered here for:

• Fixing warped rotors
• Cleaning contaminated pads
• Ensuring pad/rotor compatibility
• Realigning misaligned calipers
• Checking all system hardware is tight

Sticking to OEM components, proper bedding, and regular maintenance will minimize problems in the future. But if the telltale pulsing returns, you’ll have the confidence and knowledge to get your brakes smoothed out in no time.