When your car makes strange sounds, it is easy to get you concerned. One of these sounds is a knocking noise from the back left wheel.
What is the cause of knocking noise back on the left wheel? Worn suspension components mostly cause it, but it can also be caused by the following:
- Lug nuts are coming loose
- Worn or loose exhaust system components
- Imperfect and loose brake pads
- Loose or worn-out shock mounting bolts
- Failing wheel bearings or splines
- Loose rear axle bar link
- Failing CV joint or ball joints
All these issues must be addressed if you want to eliminate the knocking noise. The good news is that everything you need is in this guide.
What Causes Knocking Noise Back Left Wheel?
If you’re hearing knocking noise from the back left wheel, the best action you can take is to figure out what is causing the issue and fix it. Below are the common causes of the knocking noise coming from the back left wheel and how you can fix them.
1. Loose Lug Nuts
Loose lug nuts are one possible cause of a knocking noise from the back left wheel that I have had to deal with. If the lug nuts are not tightened properly or have become loose over time, they can cause the wheel to wobble slightly while driving.
It is an issue that has seen lots of . The wobbling motion can result in a knocking or rattling noise, slightly different from the engine rod knock. You will also most hear it when driving over bumps or uneven surfaces. The noise is typically more noticeable at higher speeds.
Solution
- Inspect the lug nuts and tighten them properly using a lug wrench or a socket wrench with the appropriate size socket.
- I recommend you tighten the lug nuts in a star or cross pattern to ensure even tightening.
- Ensure you apply firm and even pressure to tighten each lug nut until they are snug or to the manufacturer’s recommended torque specification.
2. Loose or Worn Exhaust System Components
Another potential cause of a knocking noise from the back left wheel is loose or worn exhaust system components. The exhaust system includes various components such as the muffler, pipes, and hangers.
If any of these components become loose or worn out, they can start vibrating and hitting against nearby parts. That includes the wheel or the undercarriage of the vehicle.
This can result in a knocking or rattling noise, especially when driving over bumps or uneven surfaces. You may also hear knocking noise when coasting on slightly rough terrain.
Solution
- I would start by inspecting the exhaust system for any loose or damaged components. Tighten any loose bolts or clamps that connect the exhaust system parts together.
- Replace any worn-out or damaged exhaust hangers. These hangers help support and suspend the exhaust system, preventing excessive movement and vibrations.
- If the muffler itself is damaged or has loose internal components, it may need to be replaced.
- You may do it yourself or consult a qualified mechanic or exhaust specialist for further diagnosis and repair.
3. Imperfect Fitment of Brake Pads
An imperfect fitment of brake pads, especially after a brake job, can also lead to a knocking noise from the back left wheel. When brake pads are not properly installed or aligned, they can move around within the brake caliper housing.
The movement can cause the pads to knock against the caliper or other nearby components. That causes a distinct knocking sound when the brakes are applied or when driving over bumps. You may also hear a slight clicking noise when decelerating, which seems to get louder as you press the brakes.
Solution
- Inspect the brake pads for proper alignment and fitment. Ensure they are securely seated within the brake caliper housing and are not loose or misaligned. I can also recommend you do brake bedding for stress testing.
- If the brake pads are not properly aligned, remove them and reinstall them correctly. Pay attention to the positioning and orientation of the pads as specified by the vehicle manufacturer.
- Consider replacing the brake pads if they are excessively worn or damaged. Installing new brake pads can ensure proper fitment and reduce the chances of knocking noises.
4. Loose or Worn Rear Shock Mounting Bolts
The shocks or struts in the rear suspension system control the movement of the wheels and maintain stability. Sometimes, the mounting bolts that secure the shock absorber or strut to the vehicle’s chassis become loose or worn.
If that happens to your car, it can result in excessive movement and play, resulting in the knocking noise as the rear wheel encounters bumps or uneven road surfaces. The sound comes from the shock of a rattle or hitting other components.
Solution
- Inspect the mounting bolts for any signs of looseness or wear. If loose, use the appropriate tools to tighten them to the manufacturer’s recommended torque specification.
- If the mounting bolts are damaged, you need to be replaced. Do it yourself or consult a qualified mechanic. If you DIY, refer to the vehicle’s service manual for the correct specifications and replacement procedure.
- Remember to regularly check the tightness of the shock mounting bolts as part of routine maintenance. This will help prevent future issues and ensure the proper functioning of the rear suspension system.
5. Rear Axle Sway Bar Link
The sway bar, also known as the stabilizer bar, is a component of the suspension system that helps reduce body roll during cornering. It is connected to the rear axle through sway bar links.
If a sway bar link becomes worn or develops play, it can cause the sway bar to move and contact other nearby components, such as the axle or frame. This will cause a knocking or clunking noise. You will often hear it when driving over uneven terrain or making turns.
Make sure the bar is tight and snug. Check the sway bar links for any signs of wear, damage, or looseness by prying it, or use your hands to move it around and check how it plays.
Solution
- If the nut is missing, replace it. If any other issues are found, replace the sway bar link with a new one that matches the vehicle’s specifications.
- I would recommend replacing sway bar links in pairs to ensure balanced performance. Consider upgrading to aftermarket sway bar links that may offer improved durability and performance, especially if the issue is recurring.
6. Failing Wheel Bearing or Splines
The wheel bearings allow smooth rotation of the wheel hub assembly, and the splines connect the wheel hub to the axle shaft. Over time, these components can wear out or become damaged, leading to several signs of wear, including excessive play, restrictions, or misalignment.
That will create a knocking or thumping noise as the wheel rotates and encounters irregularities on the road. You need to check for excessive play of the wheel when you shake it horizontally and vertically. Listen for any grinding or growling noises when spinning the wheel by hand.
Solution
- If you suspect a failing wheel bearing or splines, do the checks mentioned or take your vehicle for inspection.
- Depending on the damage severity, you may need to replace the wheel bearing, or splines may need to be replaced.
7. Failing Ball Joints or CV Joints in the Axle/Half Shaft
If your vehicle has an independent rear suspension (IRS) or separate rear suspensions, a failing ball joint or CV joint could also cause the issue. Typically, this is a problem you should leave to a technician to troubleshoot. However, you can also do it yourself.
You can check if the ball joint or CV joint is if:
- The boot is worn out
- There is grease all around the boot.
- Inspect the ball joints and CV joints for any signs of wear, damage, or grease leakage.
- Excessive movement or play in the ball joints or CV joints.
- Knocking or clunking noises when going over bumps or during turns.
Solution
- If you suspect a failing ball joint or CV joint, it is crucial to have a qualified mechanic inspect the vehicle. The technician will assess the condition of these components and recommend the appropriate repairs.
- Depending on the extent of the damage, the ball joints or CV joints may need to be replaced. This complex repair requires specialized tools and expertise, making it best suited for professional mechanics.
Conclusion
The knocking noise of the left wheel can be a safety issue like a loose lug nut or a maintenance issue like a loose suspension or exhaust part. Either way, you must troubleshoot the cause to know what action to take to fix the problem.
Some solutions to these causes are easy to fix yourself, but some might demand auto repair skills and tools. You can attempt them if you feel comfortable. If uncomfortable, I recommend taking your vehicle to an auto shop.
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