How To Know When Struts Are Bad

Diagnosing failing struts is a crucial skill for any DIY mechanic or car enthusiast. Not only does it ensure a smoother and safer ride, but identifying these issues early can prevent more costly repairs down the road. This guide provides a comprehensive overview of how to identify bad struts, combining technical knowledge with practical troubleshooting tips.

Purpose of Understanding Strut Condition

Knowing when your struts are failing is important for several reasons. Primarily, bad struts compromise your vehicle's handling and braking performance, potentially leading to accidents. Worn struts increase stopping distances, reduce steering responsiveness, and can cause instability, especially during emergency maneuvers. Secondly, neglecting strut replacement can accelerate wear on other suspension components, such as tires, ball joints, and control arm bushings, resulting in a more extensive and expensive repair bill later on. Finally, understanding strut condition is essential for proper vehicle maintenance and tuning, whether you're aiming for a comfortable daily driver or a high-performance machine. It ensures optimal ride quality and handling characteristics.

Key Specs and Main Parts of a Strut Assembly

A strut assembly is a critical part of a vehicle's suspension system, integrating several components into a single unit. Understanding these components and their specs is key to accurate diagnosis:

Strut Cartridge/Shock Absorber: This is the hydraulic cylinder filled with fluid (often oil or gas) that dampens suspension movement. It controls the rate at which the spring compresses and rebounds. Key specs include damping force (resistance to movement), rebound rate, and compression rate. These are typically proprietary to the strut manufacturer.
Coil Spring: The coil spring absorbs and stores energy from bumps in the road, providing the initial cushioning effect. Specs include spring rate (measured in lbs/inch or N/mm, indicating how much force is required to compress the spring a given distance), free height (length of the spring when unloaded), and compressed height (length of the spring when fully compressed).
Strut Mount: The strut mount connects the strut assembly to the vehicle's chassis. It typically contains a rubber or polyurethane bushing to isolate noise and vibration. A bearing (or similar mechanism) is often integrated to allow for steering movement in front struts.
Jounce Bumper (Bump Stop): This prevents the suspension from bottoming out during extreme compression. It acts as a secondary spring, progressively increasing resistance as it compresses.
Dust Boot: Protects the strut rod from dirt, debris, and moisture, extending the life of the strut cartridge.

Symptoms of Failing Struts

Recognizing the symptoms of bad struts is the first step in diagnosis. Here are some common indicators:

Excessive Bouncing: If your vehicle continues to bounce several times after hitting a bump, the struts are likely not dampening the suspension movement effectively. This is often called the "bounce test," though it is very subjective.
Nose Dive During Braking: A significant forward dip of the vehicle's front end when braking hard indicates that the front struts are not properly controlling weight transfer.
Squat During Acceleration: Similar to nose dive, excessive rearward dip during acceleration suggests failing rear struts.
Uneven Tire Wear: Worn struts can cause tires to bounce and skip, leading to cupping or irregular wear patterns.
Leaking Fluid: Visible fluid leaking from the strut cartridge is a clear sign of seal failure and compromised damping performance.
Clunking or Rattling Noises: Worn strut mounts or internal strut damage can produce noticeable noises, especially when driving over bumps.
Poor Handling and Steering Response: If your vehicle feels unstable, wanders on the road, or exhibits delayed steering response, worn struts could be the culprit.
Vibration: Increased vibration, especially at higher speeds, can be another sign of strut wear.

How Struts Work

Struts combine the functions of a shock absorber and a suspension support. As the wheel encounters a bump, the coil spring compresses, absorbing the initial impact. The strut cartridge (shock absorber) then controls the rate at which the spring compresses and rebounds. Inside the strut cartridge, a piston moves through hydraulic fluid. Orifices (small openings) in the piston restrict the flow of fluid, creating resistance. This resistance dampens the spring's oscillation, preventing excessive bouncing and maintaining vehicle stability. The strut also plays a structural role in the suspension, supporting the vehicle's weight and maintaining wheel alignment.

Real-World Use: Basic Troubleshooting Tips

Here are some practical troubleshooting steps to help you diagnose strut issues:

Visual Inspection: Carefully inspect the struts for signs of leaking fluid, damage to the dust boot, and corrosion. Pay close attention to the strut mounts for cracks or deterioration.
The Bounce Test: Push down firmly on each corner of the vehicle and observe how it rebounds. Compare the rebound characteristics of each corner. Excessive or uneven bouncing indicates potential strut problems. This is a basic test but can be misleading.
Road Test: Drive the vehicle over various road surfaces and listen for unusual noises, such as clunking or rattling. Pay attention to the vehicle's handling and steering response.
Tire Inspection: Check your tires for uneven wear patterns, such as cupping or feathering, which can be indicative of strut problems.
Professional Inspection: If you're unsure about your diagnosis, it's always best to consult a qualified mechanic for a professional inspection. They have specialized tools and expertise to accurately assess the condition of your struts and suspension.

Safety Considerations

Working with struts can be dangerous due to the compressed coil spring. Never attempt to disassemble a strut assembly without the proper tools and training. A compressed coil spring stores a significant amount of energy and can cause serious injury if it is released unexpectedly. Always use a spring compressor designed for strut work, and follow the manufacturer's instructions carefully. Wear safety glasses and gloves to protect yourself from debris and potential injuries. If you are not comfortable working with compressed springs, it's best to leave the strut replacement to a professional.

Conclusion

Understanding how to diagnose bad struts is essential for maintaining your vehicle's safety, handling, and ride quality. By recognizing the symptoms, understanding the components, and following the troubleshooting tips outlined in this guide, you can confidently assess the condition of your struts and make informed decisions about maintenance and repairs. Remember to prioritize safety when working with suspension components and consult a professional mechanic if you have any doubts or concerns.

We have a detailed diagram of a strut assembly available for download. This visual aid can further enhance your understanding of the components and their relationships. Contact us to request the file.