EagleTribune.com, North Andover, MA

January 27, 2013

Shocks too often neglected

Under the Hood
Brad Bergholdt

---- — I am the original owner of a 1991 Ford Ranger Super Cab 4x4 pickup truck. The truck has 220,000 miles on it, and it’s still going strong. It has 4-wheel drive and the 4.0-liter V-6 engine. My question is: Should I replace the shocks? The current shocks are from the factory.

My truck has not done a lot of heavy hauling over its life — some, but not much. I have inspected each shock and see no evidence of leaking fluid. I have also tested them by pushing down on each corner of the truck as hard as I could and observing the motion of the truck. In each location I noted very little movement immediately after I stopped pushing.

I’m thinking that due to the age of these guys and the miles they have carried me around that maybe I should just go ahead and replace all four shocks. It’s something I can do myself, and I plan on keeping this truck a long time. What do you think?

It’s time to change these. Shock absorbers are probably the most neglected component on an automobile or light truck, as their function isn’t obvious under many driving situations. Shock absorbers, also called shocks or struts, are typically a tube-shaped component containing a piston, orifice, control valves, hydraulic fluid and compressed nitrogen gas. Shocks absorb and dissipate suspension energy to provide improved ride comfort, increased vehicle stability, consistent tire-road surface contact, and reduced wear on tires and the suspension system.

Every road-going vehicle contains components that are considered un-spring weight. These include the wheel, tire, brakes, hub/knuckle, axle or differential, and suspension components. When a wheel hits a bump, these parts move with the wheel, compressing the spring, which may be a coil, leaf or torsion bar. After the bump, these collectively heavy parts are pushed downward by the spring, overshooting their original position, which sets up additional unwanted oscillations. Without the shock absorber’s damping action, these parts would continue to cycle many times, upsetting tire traction, ride comfort and vehicle control.

A shock’s internal components wear out over time, lessening efficiency. External leakage of fluid may also occur, which is the most noticeable failure symptom. The folks manufacturing shocks and struts recommend renewing them every 50,000 miles, although road conditions, vehicle type and driving habits should also be factored. I was a former shock neglecter until one day, taking a downhill turn at about 50 mph, I came to an unanticipated washboard road surface. Without obvious vehicle bumping, there was a clear decrease in tire traction as my SUV almost vibrated itself off the road. I renewed all four shocks and tried that same turn again several times. There was a significant difference in road-holding ability, as well as an improvement in general stability under other driving conditions.

With my driving routine and slower-moving, stiffly sprung truck and SUV, I won’t likely be a 50,000-mile shock replacer. Other folks with more challenging road conditions and commutes and higher-performance vehicles, driven faster, perhaps should be. Testing shocks by pushing up and down on the bumper is the traditional test, but only a terrible shock on a soft-sprung car seems to show up noticeably.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at under-the-hood@earthlink.net; he cannot make personal replies.