Auto Service World
Feature   October 1, 2001   by Jim Anderton

Bump Stoppers

As ride control technology gets more sophisticated, so do service issues

Call them shock absorbers, struts or dampers, ride control ranks with braking as a primary safety and comfort service segment for all cars and light trucks. Ride control issues tend to be simple to diagnose and products easy to install, leaving a deeper knowledge of spring damping unknown to many technicians. That’s unfortunate, because it’s not only interesting, but will become very important as active ride control systems work their way down into mainstream cars and light trucks. For the present, however, ride control is most often “Re and Re” work, with heavy pricing pressures and a significant amount of entry-level product.

At the bottom end, the relatively new factor of “reman” struts from suppliers such as Visiontech is challenging the conventional order of “good, better, best” with low prices and warranties as long as “lifetime”. The majors are fighting back with low cost product of their own, although there’s no indication that they will offer remanufactured products in either the near or long term. As Jim Betournay, national account manager for branded products at ArvinMeritor Light Vehicle Aftermarket (Gabriel) explains: “We understand that consumers are looking for an economy product. We have an economy strut to go up against the rebuilders like Visiontech. We’ve priced it to their market.” Betournay notes that new product is priced roughly 20 percent higher than reman, although core charges and the cost of handling cores should be considered when choosing economy product. Betournay also notes that installers considering reman product should make sure that similar strut technologies should be installed on both sides of the vehicle, since different internal valving will give different ride characteristics.

Every shop would like to install premium ride control products, and at the middle and upper end, technologies centre on velocity sensitive valving, allowing the shock or strut to react differently to varying road conditions. The goal is good handling with acceptable ride quality, and all major manufacturers have a variation on the velocity-sensitive theme. Do consumers understand that there’s advanced tech inside the tube? “I don’t think so, says Betournay. “The marketplace understands it, but the end consumers don’t. I don’t think they’re looking for VST or Reflex; they’re looking for quality product at a good price.”

Whether the consumer can see the good stuff inside or not, it helps if the installer can explain why good product is worth the investment. That process begins by describing why what shocks and struts do. “Shocks dampen the spring oscillations between the tire and the body as well as improve tire adhesion. It converts the kinetic energy of that motion into heat”, says Mark Christiaanse, director of product management, Tenneco Automotive (Monroe). As in most automotive systems, heat is an enemy; in damping technology it’s dissipated through the reserve tube, which also explains why fade is more prevalent as leaking struts or shocks age. Even with adequate remaining oil to operate the damper, as the overall oil quantity drops, the ability to absorb heat decreases. That means that performance will suffer as the product ages, even though oil loss is within the safe range, making service a sensible suggestion before the shock or strut body is soaked in oil.

Replacement products are often marketed by gas pressure and construction type, which can add to consumer confusion. “The difference between low pressure and high pressure is normally the difference between mono tube and twin tube”, declares Christiaanse. “Mono tube design has the chamber of gas separated from the oil by a disk or piston. Gas pressure is high because it takes the compression of the rod as it goes into the unit. In that design, there’s no aeration because the area of the fluid is separated from the gas. The twin tube design has the potential of aeration, which is controlled by the gas pressure. The pressure needed to control aeration is relatively low. You can also use gas pressure to tune the unit. Higher pressure makes the force necessary to operate valving and bleeds higher. You can change damping with pressure. In general high pressure for monotube and low pressure for twin tube.”

Oil aeration control can be achieved with as little as 20 psi, so at least some of the gas pressure is used to tune the ride. From a service perspective, that means that there’s another way for the product to wear: loss of pressure. It’s not normally a major factor, but accident damage or encounters with rocks or debris off-roading are signs of potential trouble.

Ride is still the ultimate determinant for ride control customers, and while that may seem self evident, consider safety as an additional selling point. Ride control engineers talk of “pitch” and “yaw” (nosedive and turn-in), and ” controlling the rates”, but all but the most savvy consumers need a safety and security argument. According to Mark Christiaanse, “In normal day to day driving, emergency stopping nosedive and the rate of dive is something consumers can relate to. In a sudden lane change, rates of pitch and yaw will change. While they (consumers) may not sense shorter stopping distances, they can definitely feel the pitch rate. In our testing a single worn shock has added as much as ten feet to stopping distances. It’s a huge difference.”

Upselling ride control customers to advanced product is always a good idea for safety reasons, but it’s also important to consider the complete job. Jim Betournay advises: “The first thing a technician should do is to sell the complete job. They do themselves a disservice by not changing the strut mounts at the same time as the struts. Often struts have been on the car for 50,000 miles, and are tired and worn out. The mounts that hold the struts in place are also worn and weak. Put a brand new set of struts on there, and what will they do to the old mounts? Technicians will have noise complaints and comebacks, and will then believe that the struts are defective. A dealer makes no money when a customer comes back with a new set of struts. Technicians should be sure to sell the complete job.”

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