Can Air In Brake Lines Cause Pulsating?

Experiencing pulsating or vibrating brakes can be alarming. You hit the brake pedal expecting a smooth stop, but instead feel shaking and pulsing through the pedal and steering wheel.

This vibration is commonly referred to as brake pulsation or brake judder. It usually happens once the brakes are warmed up after driving for a bit.

What causes this frightening brake pulsation? Can air trapped in the brake lines lead to brake pulsation? Let’s find out.

What is Brake Pulsation?

Brake pulsation refers to the noticeable vibration or shuddering sensation through the brake pedal, steering wheel, or entire vehicle when the brakes are applied.

As you press down on the brake pedal, you can feel rapid pulses of shaking and vibration. It feels as if the vehicle is passing over rumble strips on the road.

Brake pulsation usually occurs once the brakes have heated up from normal use. It is more common to experience it after highway driving or descending a long downhill grade when brake heat builds up.

Light brake use around town is less likely to create the proper conditions for brake pulsation. You’ll usually feel it more prominently when braking from higher speeds.

What Causes Brake Pulsation?

The most common cause of brake pulsation or vibration is warped brake rotors.

Rotors can become warped from:

• Overheating – Excessive heat beyond the rotor’s cooling capacity can warp rotors. Repeated hard braking situations or sticking brakes can overheat rotors.
• Uneven resurfacing – If rotors become heavily scored or worn but are resurfaced unevenly, thickness variations can cause pulsation.
• Excessive runout – If a rotor develops substantial “runout” (inconsistency in the rotor’s circularity), brake pulsation can occur.

As the brakes clamp down on a warped, uneven rotor surface, the high and low spots create pulses you can feel through the brake pedal and steering wheel.

Can Air in Brake Lines Cause Pulsation?

Trapped air in the brake hydraulic system is undoubtedly a serious issue, one that can lead to hazardous braking problems. However, contrary to what some may think, air in the brake lines does not actually generate the sensation of brake pulsation.
While air in the lines causes other braking defects like a soft, spongy pedal feel, decreased braking power, and expanded stopping distance, it does not directly translate into vibration or pulsation through the brake pedal.

At worst, excessive air can lead to complete brake failure. But the shuddering, shaking brake pedal pulsation that drivers often find alarming is almost always traced back to warped brake rotors, not air in the lines. So in summary, despite being a problem, air in the brake lines is not the true culprit behind brake pulsation – warped rotors cause those frightening vibration issues.

What Are the Dangers of Brake Pulsation?

You should have any suspicious brake vibration inspected immediately, as brake pulsation can escalate into a dangerous situation.

Prolonged driving with warped rotors can intensify the problem or lead to other brake defects:

• Increased wear – Brake pads wear unevenly and rapidly as they clamp on the uneven rotor surfaces. This shortens pad life.
• Brake failure – Severely warped rotors can crack under thermal stress. Pulsation can damage brake caliper components. In extreme cases, complete brake failure may occur.
• Reduced control – Brake pulsation affects braking effectiveness. This makes it harder to control the vehicle and increases stopping distance.

Dangers of Brake Pulsation
Increased brake pad wear	Uneven pad wear from pulsating on warped rotors
Brake failure	Cracks or component damage from excessive rotor warping
Reduced vehicle control	Longer stopping distance due to uneven braking forces

Signs of Brake Pulsation

How do you know if your car has brake pulsation issues? Here are the common signs:

• Shuddering brake pedal – As you press the pedal, you’ll feel rapid shaking and pulsing through the pedal.
• Vibrating steering wheel – A loose or shaking steering wheel upon braking indicates rotor problems.
• Vehicle vibration – The entire car shakes when braking due to forces from the warped rotors.
• Noise – In severe cases, a grunting or grinding noise may accompany the pulsation.
• Reduced braking power – Brake performance deteriorates, with longer stopping distances.

Brake pulsation mainly occurs once the brakes are hot from use. Be alert for any vibrations arising after prolonged driving. Also pay attention to brake smoothness after descending hills or towing trailers.

What To Do if You Experience Brake Pulsation

If you feel any suspicious brake pedal vibration or pulsation in your vehicle:

• Stop driving the vehicle immediately. Continuing to drive with severe brake pulsation is unsafe.
• Have the brakes inspected. Diagnose the extent of the issue. Look for signs of warped rotors.
• Resurface or replace rotors. Matching high quality replacement rotors to the existing hub and brake system is optimal.
• Inspect brake pads. Look for uneven pad wear. Replace pads if needed.
• Assess related components. Make sure the brake calipers, hoses, master cylinder, and other parts are in good operating condition.
• Test drive vehicle. Confirm that brake pulsation is eliminated prior to returning to normal driving.

Ignoring significant brake pulsation risks accelerated wear, loss of control and breakdowns. Address it promptly to restore safe braking.

How To Prevent Brake Pulsation

Preventing brake pulsation should be a priority for all drivers. The unnerving shaking and vibration of brake pulsation can elevate into serious safety hazards if left unchecked. Follow these proactive measures to help avoid the conditions that breed brake pulsation:

• Drive carefully to reduce brake heat buildup. Avoid situations that require heavy, repeated braking which can overheat the rotors.
  • Take it easy on long downhill stretches. Descend gradually using engine braking.
  • Allow plenty of following distance so you can brake early and gently versus waiting until the last moment.
• Let brakes cool off after heavy use before continuing your drive. Don’t immediately jump back on the highway after descending a mountain pass or hauling a heavy load. Give the rotors time to dissipate heat and return to normal temperatures.
• Inflate tires properly. Underinflation promotes uneven tread wear and reduces stability, which increases stopping distances and brake heat.

Staying on top of maintenance is equally important:

• Replace brake pads before they reach minimum thickness. Worn pads reduce effectiveness and increase heat.
• Have rotors resurfaced or replaced as needed. Machining can correct moderate warping. Badly warped rotors usually require replacement.
• Use premium replacement brake parts designed specifically for your vehicle’s braking system. Quality components last longer and perform better under stress.

While you can’t always avoid ever overheating your brakes, smart driving habits and diligent maintenance will help fend off brake pulsation issues down the road. But if those frightening vibrations ever manifest, have your brakes checked immediately.

Frequently Asked Questions

Does brake fluid cause brake pulsation?

No, the type or condition of brake fluid does not directly cause brake pulsation issues. However, moisture-contaminated brake fluid with a low boiling point can potentially contribute to brake components overheating, which may promote rotor warping.

Do bad brake calipers cause brake pulsation?

Faulty brake calipers can trigger vibrations when braking due to uneven pad pressures. But the root cause of classic brake pulsation felt through the pedal is almost always warped rotors. Calipers themselves don’t warp rotors.

Will new brake pads stop brake pulsation?

Not usually. While resurfacing or replacing rotors is generally required, just replacing brake pads alone often will not eliminate brake pulsation. The issue stems from rotor thickness inconsistencies, not the pads themselves.

Can I drive with brake pulsation?

It’s not recommended. Severe brake pulsation can worsen and is unsafe. Have your brakes checked immediately if you feel any sustained vibration when braking. Address the cause before normal driving.

Should I resurface or replace brake rotors?

For moderate warping, resurfacing rotors may correct pulsation. But badly warped rotors usually need replacement. Consult a mechanic to determine the best fix. Use premium quality replacement rotors designed for your vehicle.

Conclusion

Brake pulsation is an alarming sensation when your brakes vibrate or pulse upon application. While trapped air in the brake lines does not directly cause brake pedal pulsation, it can lead to other serious braking problems. The primary cause of brake pulsation is warped brake rotors.

This issue needs prompt diagnosis and correction to avoid accelerated wear and potential brake failure. Address any perceived brake pedal vibration immediately by having your brake system inspected and rotors resurfaced or replaced as needed. Restoring properly smooth braking function reduces risks and provides essential peace of mind when driving.