There are a few things that you should never do when you’re driving your car. And one of the most important warning signs you should not ignore is any strange sound or movement coming from your brakes.
The safety of you and your passengers, not to mention other road users, depends on your ability to stop your car safely.
So, a knocking sound when you’re braking is a cause for concern and should be investigated as soon as possible.
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What Causes a Knocking Noise When Braking?
The knocking sound when braking could be a result of worn brake pads that require replacement. There could also be air in your brake system. In older cars, the brake rotor may be warped or cracked. You may have worn bushings on the control arms or bolts holding the brake caliper may be loose.
If the knocking noise is loud and insistent when you brake, then take your car to a mechanic as soon as possible. Describe what you are hearing and get the mechanic to diagnose the problem.
If you have the necessary DIY knowledge and tools, then you can investigate the problem yourself.
To check for worn brake pads, you need to remove the wheels so that you can access the brake calipers.
Replace Worn Brake Pads
Once the car is jacked up, place a brick or block behind the rear wheels to prevent the car from rolling backward.
If you can, use a stand to support the car while you are working on it, as hydraulic jacks have a tendency to fail when you least expect it.
Once you’ve removed the wheel, have a look at both the inner and outer brake pads to see how much friction material remains on the pad. If your car has a brake wear sensor, a light on your dashboard will warn you that your brakes are worn.
A visual inspection will reveal the state of your brake pads and if they are worn beyond the wear marks, then replace them. As a rule, replace brake pads that have 1/8th of an inch (3mm) or less friction material left.
Bleeding Air Out of Your Brake Lines
To check if you have air in your brake system, you’ll either need a brake bleeder kit or a length of hose and a bottle into which you can pour some brake fluid.
Another indication that there’s air in your brake lines is a spongy feel to the brake pedal.
With the car on a level surface, release the handbrake after placing blocks behind and in front of the wheels.
For safety, leave the vehicle in gear if it is a manual transmission or in park for automatics.
Always bleed the brake lines according to the manufacturer’s specifications.
Start by wiping off the brake fluid reservoir cap with a cloth to remove any oil or other debris that may enter the bottle when you remove the cap. When it’s clean, unscrew the cap and siphon off most of the brake fluid, leaving a little in the bottom of the reservoir.
Top off the reservoir with new brake fluid. Make sure that you use the correct type as specified in the owner’s manual.
Never allow the reservoir to empty as it will introduce air into the brake system. Replace the cap on the reservoir and move to the first wheel, furthest away from the brake master cylinder.
Attach your bleeder tool hose to the brake bleeder valve and locate your wrench over the valve. Turn the wrench so that the valve opens and brake fluid enters the bleeder tool tube.
Make sure that the bleeder tool has brake fluid in it and that the end of the tube is below the surface.
With the valve open, have a friend or family member gently push down on the brake pedal. Let them hold the pedal to the floor and then tighten the valve with your wrench before they release the pedal.
Have them pump the brake pedal while the bleeder valve is closed to build up pressure before opening the valve again to allow any bubbles in the brake line to travel into the bleeder tool.
Do this several times until no more bubbles appear in the tube and the pedal is stiff when it is pumped.
Repeat the process on all four wheels until you have removed all the air from the system.
Check the level of fluid in the brake reservoir after you finish each wheel to make sure that there is enough in it.
If the level has dropped below the minimum line, top up the reservoir before moving to the next brake line.
Replacing a Warped or Cracked Brake Rotor
When you check the brake pads for wear, run your finger along the face of the brake disk (rotor).
The face should be smooth, without any ridges, chips, or cracks. The rotor should also be perfectly true. If it appears to wobble back and forth, then it is warped and must be replaced.
To replace the rotor, you’ll have to remove it from the wheel hub. Many rotors don’t have any bolts holding them in place, but some may have a screw.
But before you do that, remove the brake pads and brake caliper. Then remove the brake caliper bracket.
Smack the outer edge of the rotor with a hammer to get it to break loose from the hub and remove it.
Fit the new roto after cleaning off any anti-rust compound that may be on it. Replace the caliper and brake pads in the reverse order of the way you took them off.
What to Do About Worn Suspension Components
If you suspect the suspension components are worn and that is what is causing the knocking sound, take your vehicle to a competent mechanic.
Unless you have the necessary tools to complete the job, it is best that you let a professional sort out your suspension.
Frequently Asked Questions About Knocking Noise When Braking
Is it safe to drive with a knocking noise?
It is not safe to drive with a knocking noise. There are many reasons why your car will make a knocking noise. Some can be simple to fix, while others may be complex and require costly repairs. Rather than take a chance and make things worse, inspect the car as soon as possible or take it to a mechanic to check it over.
Can shocks make a knocking noise?
Worn shock absorbers can make a knocking noise. You’ll also probably feel the car veering off to one side. The bushing may also be cracked or broken, so the sooner you get it fixed the better.
What causes a clunking or knocking sound at the rear end?
The rear suspension struts or worn shock absorbers may cause a clunking noise to come from the rear of your car. On cars with disk brakes on the rear hubs, you may have worn brake pads or a warped brake rotor.
Conclusion On What Causes a Knocking Noise When Braking
Driving with a knocking noise when you brake is dangerous.
You should investigate the possible causes as soon as possible and take the vehicle to a mechanic if you cannot solve the problem yourself.