How To Know If Struts Are Bad

So, your ride's starting to feel a little… bouncy? Handling isn't as sharp as it used to be? It might be time to take a good, hard look at your struts. As experienced DIYers, you know that suspension components are crucial for safety and performance. This article provides a technical breakdown of how to diagnose worn or failing struts, giving you the confidence to tackle this task yourself or at least be well-informed when you take your car to a professional.

Purpose: Why This Matters

Understanding strut diagnosis is vital for several reasons:

• Safety: Worn struts significantly reduce braking effectiveness and increase stopping distances. They can also compromise handling, especially in emergency maneuvers.
• Performance: Fresh struts restore optimal handling and ride comfort, improving the overall driving experience.
• Cost Savings: Identifying and addressing strut issues early can prevent more extensive damage to other suspension components, such as tires, ball joints, and control arms. Neglecting worn struts often leads to premature tire wear and further component failure.
• Knowledge: For modders and tuners, diagnosing strut issues is essential when upgrading or modifying suspension systems. You need to know the baseline condition of your components before making changes.

Key Specs and Main Parts

Let's break down the anatomy of a typical strut assembly. While designs vary slightly between vehicle makes and models, the core components remain consistent.

• Strut Body (or Damper): This is the main hydraulic cylinder that absorbs shocks and controls suspension movement. Inside, you'll find a piston moving through oil or gas, generating damping force.
• Coil Spring: This provides the primary support for the vehicle's weight and determines ride height. The spring's compression and extension absorb bumps and undulations in the road.
• Strut Mount: Located at the top of the strut assembly, this mount connects the strut to the vehicle's chassis. It typically incorporates a rubber or polyurethane bushing to isolate noise and vibration. Some strut mounts also include a bearing that allows the strut to rotate as the steering wheel is turned.
• Dust Boot and Jounce Bumper: The dust boot protects the strut rod from dirt and debris, while the jounce bumper prevents the suspension from bottoming out during extreme compression.

Important specifications to keep in mind (which you'll find in your vehicle's service manual) include:

• Ride Height: The distance between a specific point on the vehicle's body (e.g., fender well) and the ground. Incorrect ride height can indicate worn springs or damaged struts.
• Damping Force: While difficult to measure without specialized equipment, this spec indicates the strut's ability to control suspension movement. A worn strut will exhibit significantly reduced damping force.
• Torque Specifications: Always use the correct torque settings when tightening strut mount bolts and other suspension fasteners. Under- or over-tightening can lead to component failure.

How It Works

The strut assembly works as a combined spring and damper. The coil spring supports the vehicle's weight, while the strut (damper) controls the rate at which the spring compresses and rebounds. When the wheel encounters a bump, the spring compresses, absorbing the energy. The strut then restricts the spring's rebound, preventing the vehicle from bouncing excessively. This damping action is achieved by forcing hydraulic fluid or gas through small orifices within the strut body. The resistance created by this process dissipates the energy and smooths out the ride.

A failing strut loses its ability to effectively control the spring's motion. This can result in:

• Excessive Bouncing: The vehicle continues to bounce after hitting a bump.
• Poor Handling: The vehicle feels unstable and prone to body roll during cornering.
• Increased Braking Distance: The struts lose control causing weight transfer, so the ABS is less effective.
• Uneven Tire Wear: Caused by inconsistent wheel contact with the road surface.

Real-World Use: Basic Troubleshooting Tips

Here's a practical approach to diagnosing strut problems:

1. Visual Inspection: Start by visually inspecting the struts for signs of damage or leaks. Look for:
   • Fluid leaks: A wet or oily strut body indicates a leaking seal.
   • Physical damage: Dents, bends, or corrosion can compromise the strut's integrity.
   • Damaged dust boot: A torn or missing dust boot exposes the strut rod to dirt and debris, accelerating wear.
   • Corroded Springs: Rust can compromise the integrity of the springs.
2. Bounce Test: Push down firmly on each corner of the vehicle and release. Observe how the suspension responds. A healthy suspension should rebound once and then settle. Excessive bouncing (more than two or three oscillations) indicates worn struts.
3. Driving Test: Pay attention to how the vehicle handles during normal driving conditions. Listen for unusual noises, such as clunking or rattling, especially when going over bumps. Observe for excessive body roll during cornering.
4. "The Rock Test": With the vehicle safely parked on a level surface, grab the top of a front tire and vigorously rock it back and forth. A properly functioning strut mount shouldn't exhibit excessive play or noise. Clunking sounds indicate a worn strut mount or ball joint.

Interpreting your Findings:

• One Corner Bounces Significantly More: This strongly suggests that the strut on that corner is worn or damaged.
• The Vehicle Pulls to One Side During Braking: This can be caused by a failing strut on the opposite side. The worn strut allows more weight transfer, reducing the braking force on that wheel.
• Uneven Tire Wear (Cupping): This pattern, characterized by alternating high and low spots around the tire's circumference, is a classic sign of worn struts.

Safety: Risky Components

Working with suspension components can be dangerous, especially when dealing with compressed springs. Always exercise caution and take the following precautions:

• Use a Spring Compressor: When removing or installing struts, always use a properly rated spring compressor to safely relieve the tension on the coil spring. Never attempt to compress a spring without the correct tools. Springs can store tremendous amounts of energy, and a sudden release can cause serious injury or death.
• Wear Safety Glasses: Protect your eyes from flying debris.
• Loosen Fasteners Before Lifting: Before raising the vehicle, loosen the strut mount bolts and other suspension fasteners. This will make them easier to remove once the vehicle is in the air.
• Support the Vehicle Properly: Use jack stands to support the vehicle's weight. Never work under a vehicle supported only by a jack.
• Follow Torque Specifications: Use a torque wrench to tighten all suspension fasteners to the manufacturer's specified torque values.
• If unsure, consult a professional! Suspension work can be tricky and dangerous. There is no shame in delegating this task to a qualified mechanic.

Important Note: It is generally recommended to replace struts in pairs (both front or both rear) to maintain balanced handling and braking performance. Replacing only one strut can create an imbalance in the suspension, leading to unpredictable handling characteristics.

By understanding the purpose, components, and troubleshooting techniques outlined in this article, you are well-equipped to diagnose strut problems on your vehicle. Remember to always prioritize safety and consult your vehicle's service manual for specific instructions and torque specifications.

We have a detailed diagram showcasing strut assembly and common failure points available for download. This visual aid will further enhance your understanding and diagnostic capabilities.