STEERING & SUSPENSION: WHERE IS THE WEAR?

Motor,  Jun 2005  by Seyfert, Karl

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Regardless of the materials used, friction and gravity inevitably cause wear that degrades steering and suspension performance on all vehicles-even those constructed of unobtanium.

It's no longer considered rare or unusual for a vehicle to travel 100,000 miles or more and still have all of its original steering and suspension components. This extended wear trend includes other areas of the vehicle as well. Engines last longer; transmissions last longer; everything lasts longer. Better cars? Better roads? Better maintenance? We may disagree on why this is true, but at least we can probably agree that it is true.

None of these parts is the same after 100,000 miles as it was at O miles, of course. In the case of steering and suspension parts, the deterioration is gradual, and it may be difficult for the driver to notice anything has changed until things have gotten bad enough to represent a safety hazard. Rather than waiting until then, it's best to take a proactive approach. Why wait until the vehicle comes in behind a tow truck to start thinking about steering and suspension wear?

Road Test

Begin with a road test. If the customer is available, take him along or have him drive to get a feel for the vehicle. Use your eyes, ears and the seat of your pants as you drive. Do you hear any unusual noises? Does the vehicle seem to bob and weave as it passes over irregularities in the pavement? Does it feel like anything unusual is going on under the vehicle?

As steering parts wear, they cause the steering to become vague and unresponsive. When suspension parts like ball joints and control arm bushings wear, they cause unfamiliar clunks and bumps as well as uneven tire wear. Loose or worn steering or suspension components can also cause a pull that occurs abruptly when the vehicle hits a bump. A steering wheel that changes positions during straightahead driving after braking is a tip-off that something is loose in the suspension or steering, causing a sudden toe change.

Many techs still attempt to check the shocks and struts using the time-honored bounce test. Each end of the vehicle is manually bounced up and down, then released. The theory is that a worn shock or strut will allow too many oscillations before the bouncing stops. What's never been established is how hard the suspension should be bounced, how many oscillations are too many and how many are just enough. You can use the vehicle's weight (instead of your own) to conduct a shock absorber test during your road test.

First, drive up a gentle grade at 25 to 35 mph. Uneven pavement is actually an advantage here. Watch the rearview mirror as you drive. If the rear end of the vehicle seems to float or bobble over the bumps, that's a tipoff that the rear shocks need attention.

Next, select a street and time when there are no cars immediately behind you. To test both the front and rear shocks, brake hard from a speed of 25 to 35 mph, but not hard enough to lock the wheels. Hold firm pressure on the pedal all the way through to a complete stop. If you don't feel a jolt at the end of the maneuver, repeat the test, and don't ease off the brakes until you feel it. Driving repeatedly over a bumpy stretch of road is also a good way to check for shock absorber fade resistance.

The same inertial weight transfer that jerks your head at the end of those hard stops will also compress the springs sufficiently to reveal a weak shock. The nose of the vehicle should sink, rise and center while the tail should mirror its motions. Any further bobbing motions indicate a weak shock. If either the front or rear fails to center effectively, one of the shocks may be sticking. Similarly, if the vehicle bobs its front or rear more than once, the shocks need replacing.

Visual Inspection

After the road test, get the vehicle on a lift and conduct a thorough steering and suspension inspection. If you suspect a steering- or suspension-related pull, check the components as you would during a prealignment inspection. Be on the lookout for loose parts and any indication of moving components such as loose control arm bolts. Clean areas or scraped paint around bolts and nuts can indicate that something that isn't supposed to is moving around. Anything that allows the wheels to point where they're not supposed to while braking can cause a pull. Loose components can also produce a single-clunk noise when the brakes are applied and the vehicle weight shifts.

While misaligned wheels will often cause a constant pull, braking can aggravate a slight pull. An uneven scrub radius can cause a severe pull under braking. A zero scrub radius will have little effect on steering pull if one front brake works harder than the other. A positive scrub radius will pull very hard, while a negative scrub radius will have a minimal effect. Most front-drive vehicles have a zero or negative scrub radius to counteract the effects of torque steer.

If the scrub radii of both front wheels are near equal, they'll cancel each other out. Problems will occur if there's a difference between the two. This can happen with bent front suspension components, wheels with different offsets or missing spacers on an aftermarket wheel.