When an SUV's ride deteriorates

Motor, Jan 2003 by Bell, Sam

After the miles add up, some SUVs may develop a ride that's more `off-road' than their owners bargained for. Here's how to bring them back to civilization.

Jarring shocks to the spinal column are not what most SUV owners were seeking when they bought their vehicles a few years ago. But just such jolts are now driving many of them to seek relief at your doors. Should you lay in a stockpile of analgesics to dull their pain, or can you lead them to some longer-term relief?

You know the complaints: harsh ride, slamming over bumps or the bobble and jiggle that leaves drivers and passengers just short of carsick. Where do you start?

Start With a Test Drive

At my shop, we begin by accompanying the customer on a brief test drive. This allows us to make sure we're both focusing on the same symptoms. This is also a good opportunity to point out any other issues we think deserve a look, as well as to observe any unusual-and potentially damaging-driving habits to which the vehicle may be subjected.

Once back at the shop, we begin at the beginning, where the rubber meets the road. When the complaint is a hard ride, we find that approximately half to two-thirds of our customers' tires are massively overinflated, usually to, and sometimes even beyond, the maximum pressure indicated on the tire's sidewall. (Probably two-thirds of the rest are woefully underinflated.)

In the wake of all the Firestone-- Ford finger-pointing over tire inflations, I hope you're well aware that no tire should ever be inflated beyond the maximum figure on the door jamb label or in the owner's manual nor any lower than the lowest recommended inflation for the vehicle in question. Any information on the tire sidewall should be used solely to determine if the tire is appropriate for the particular application. Those who bend these rules may well be found liable by a jury of their peers later! 'Nuff said.

Of course, we also take this opportunity to inspect the suspension and steering for any excessive play or looseness, as well as for any binding. And here in Ohio, where the orange barrel used to mark construction zones is supplanting the red carnation as our state flower, broken springs are not uncommon either.

We also make it a point to inspect the suspension components in both loaded and unloaded positions. A loose stabilizer bar mounting bushing, for example, may appear to be just fine when the wheels are hanging in the air on the lift, while the play may be readily detectable when the truck is resting on the ground in its normal position. Likewise, many ball joints will reveal their shortcomings only when loaded, while the load must be removed from others for proper inspection.

Because SUVs are occasionally used as intended-that is, for off-road or heavy-duty applications-it's a good idea to double-check all the bump stops and steering stops for damage...and to make sure they're actually there. A missing suspension stop can cause a great deal of noise and customer anxiety over a steep driveway apron or a deep pothole. Be sure to properly lube all steering stops as part of every routine undercar service.

If circumstances allow, it's a great idea to have your customer present while you do this preliminary inspection work. Not only does it build trust in your expertise, it also simplifies the job of explaining later what the components are and how they interrelate.

The Bounce Test

I've always enjoyed watching the way some technicians go about testing shock absorbers. Most rely heavily on the so-called bounce test, in which they try to force the truck's springs to compress and release sufficiently to catch a worn shock allowing too many oscillations. This is a nice trick, probably discovered by a big guy. Small guys like me have to find another way. I make the following shock absorber test a part of my diagnostic test drive routine.

First, drive up a gentle grade at 25 to 35 mph. If the pavement is a bit rough, so much the better. As you drive, look carefully in the rearview mirror. If the rear end of the truck seems to float or bobble, that's a tip-off that the rear shocks need attention.

Next, test both the fronts and rears in unison, making sure to select a street and time when there are no cars immediately behind you. Brake hard from a speed of 25 to 35 mph, but not so hard that you lock the wheels. Hold even, firm pressure on the pedal all the way through to a complete stop. If you don't feel the inertial jolt at the end of the maneuver, do it again, and don't ease off the brakes until you do. It's a good idea to drive over a prolonged bumpy stretch of road and repeat this test as a check for shock absorber fade resistance.

The same inertial weight transfer phenomenon 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 truck 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 truck bobs its head or tail more than once, the shocks need replacement.