Diagnose shocks and struts

How to diagnose shocks and struts:

It’s easy to diagnose a completely failed shock or strut - dripping fluid, cracked mounts, or a bent piston rod are common indicators. But how do you diagnose shocks at struts that look OK but are worn to the degree that they compromise handling, comfort, and driving safety?

Here’s how to road test a vehicle to diagnose shock and strut performance.

A good shock and strut performance road test begins with a well-planned route. Ideally, this will have a few different types of road surfaces and some potholes or speed bumps. The route doesn't have to be long - a mile is sufficient. When you do testing, be consistent. Use the same route every time and drive every vehicle the same way at the same speed. You don't need to drive fast, but you will need to see, hear, and feel how the vehicle operates at normal speeds.

Before you conduct the road test, do a vehicle inspection. Worn or failed suspension components or low tire air pressure can cause higher scores.

Drive the vehicle at a steady speed and take note:

Is it as smooth and quiet as you would expect, or do you have excessive road noise and harshness?
Are the shocks helping to keep the vehicle steady, or is it bouncing excessively after bumps and potholes?

The suspension should absorb the bumps and recover quickly. Excessive bouncing after bumps or potholes is a sign of shock and strut wear.

For the next two diagnostic maneuvers, you'll need to ensure you're on a safe stretch of road with little or no traffic.

Do a quick lane change. Does the steering respond immediately, or is there a delay?
When you do a fast lane change and then return to the original lane, is the vehicle in control, or does the steering feel delayed or require an extra correction?

If the shocks are properly controlled, the body movement should feel well-controlled, and the body should quickly return to a stable stance.

For the final test, hit the brakes hard like you would in a panic stop.

Does the vehicle stop quickly and evenly, or does it feel like only the front brakes are working well?
The vehicle's nose should dip, then quickly recover. If the vehicle's nose bounces excessively at the end of the stop, it’s a sign that the shocks can no longer control the vehicle as designed.

Now, you can score how the vehicle performed using the KYB ride control exercise worksheet.

Download the KYB Ride Control Conditions Worksheet

You'll rate the performance for nose-dive acceleration, squat, steering, and body movement. Each of these will be scored 0 to 5. Lower scores indicate the vehicle is performing as designed, while higher scores indicate excessive movement.

If the total score is five or less, it's likely the vehicle is operating close to its designed specifications.
Any score greater than six indicates the body and tires have excessive movement, and new shocks or struts should be recommended to the customer.
Show your customers their vehicle’s score. This will help customers understand their vehicle's current performance level and how new suspension components can restore better handling and control.

You can become a shock and strut diagnostic expert faster by driving a few vehicles both before and after the new shocks are installed. You’ll see the difference new shocks and struts make.