Auto Service World
Feature   April 1, 2002   by Auto Service World

Cover Story: Thinking Outside the Box

What Light Trucks' Move From Steering Box to Rack and Pinion Means to You

A decade ago, when the light truck and sport-utility vehicle craze hit big, it was welcomed with open arms by the automotive aftermarket. It wasn’t just the promise that the relatively small number of models could turn back the clock on parts proliferation that prompted the warm reception; it was what parts they needed.

Light trucks like the Ford F-Series pickups, what was then termed the General Motors C/K series, as well as many sport-utility vehicles, weren’t just variations on a theme below their skins; they were variations on a theme that the traditional aftermarket was well equipped to handle.

While the underside world of the car had long gone to MacPherson strut and double-wishbone suspensions, trucks (both of the pickup and SUV variety) had stayed with shocks and conventional suspensions, which were, well, conventional. Steering systems were the same. While cars had universally adopted the rack and pinion arrangement, the most popular selling vehicles, the pickup/SUV category, stuck with the steering box and parallel linkage steering arrangement. They were simple to understand even for aging technicians who hadn’t kept their skills up to date, and because problems could be fixed piecemeal–an idler arm here, a parallel link there–steering geometry problems didn’t have to be expensive to fix.

Now, this whole reality appears to be changing.

Just take the 2002 Chevrolet Silverado for example. While the 1500 and 2500 models across the lineup look much the same in 2WD and 4WD configurations, flip them upside down and they might as well be completely different vehicles. Just look at specs:

Front: independent with computer selected torsion bars for 1500 4×4 and all 2500 models, computer-selected coil springs for 1500 2WD models, gas-pressurized shock absorbers, maintenance-free wheel bearings, 32-mm stabilizer bar for 2WD models, 30-mm stabilizer bar for 4×4 models.

Rear: solid axle with semi-elliptic, variable-rate, two-stage multileaf springs, gas-pressurized shock absorbers.

Steering type: 1500 4WD & 2500: power recirculating ball;

1500 2WD: power rack-and-pinion.

It’s amazing how so many implications can be included in so few words. Aside from the different steering systems, items like different diameter stabilizer bars are bound to cause the aftermarket fits over parts proliferation, even in bushings alone. Some suppliers say that the bushings now outsell ball joints two to one, a complete reversal of the previous split. And the transition from torsion bar to coil spring layout is bound to surprise at least a few technicians. That’s not even considering the SLA torsion-bar setup of the so-called Heavy-Duty models, or the addition of Quadrasteer rear-wheel steering on selected versions of General Motors’ best selling truck.

Here’s how that system is described as it appears on the GMC Sierra Denali:

Steering type:

AWD Sierra Denali: Quadrasteer four-wheel; front: hydraulic power, recirculating ball; rear: electrically powered: (system also uses front steering wheel position sensor, steerable solid hypoid rear axle, electric motor-drive actuator and control unit);

1500 4WD, 2500: power, recirculating ball;

1500 2WD: power, rack-and-pinion.

Interestingly, the Quadrasteer-equipped models will only have a rack at the rear–the Quadrasteer unit–while retaining the traditional steering arrangement for the front wheels.

And the Yukon is touting a power, electronic, recirculating ball system with what GM calls the EVO variable-assist system.

It is certainly a very different world from what the aftermarket had come to think of as a conglomerated light truck/SUV market.

“There are several reasons. Currently about 19 vehicles in the light truck end have racks. Of that there are about five with 4WD,” says Robert Bean, director of product development and product assurance, Mevotech Inc.

“Part of that is the weight, downsizing to meet the CAFE standards (for fuel mileage), using aluminum, and part is shorter wheel bases. A rack will fit into a lot more unique spaces (than a conventional system).”

“Rack and pinion steering assemblies can potentially provide a cost savings to the OEM customer through the elimination of the steering box and parallel linkage design,” adds Jim Graham, manager, service and aftermarket engineering at Delphi Saginaw Steering Systems.

Bean agrees that the steering rack is indeed much more economical from an OEM perspective–one rack versus a whole basket of discrete parts–but adds that as vehicles have downsized there simply isn’t the need for as much brute force to get the wheels to turn.

He adds that many of the systems going onto these vehicles are incorporating some sophisticated technologies. He picks out the four-wheel steering system as an example. “You’re going to see a lot more down the road, and once the 42-volt systems kick in you’re going to see so much more of this happening.”

He is, of course, referring to the coming use of 42-volt systems in place of the current 12-volt electrical system currently used in all vehicles. Those higher-voltage systems will allow many of the current hydraulically actuated systems, like steering and braking systems, to use electric motors instead. Those developments are some ways off even for the OEM world, even further off for the aftermarket. Yet the aftermarket is not going to escape the influx of technology in the same way that light trucks and SUVs allowed them to do years ago.

“Steering is one of those systems that has been quietly changing,” says Bean. “There are a lot more plastics, pre-loads, tempered springs, etc. The reason you do it is low torque and to help absorb road force. Today you find that a lot of the components are a highly polished polymer. Years ago, 35 to 55 ft.-lb. was the acceptable rotational torque at the joint. Now we’re down to 20 to 30 ft.-lb.

“Steering is something that we don’t hear too much about, but it has been quietly evolving.”

It’s not that anyone needs to run off in a panic about the changes, though.

“In the short term, minimum impact is expected in the aftermarket based on volume and core availability,” says Graham. “For the long term, with the introduction of more models into the market place, along with potential strong sales, the warranty and independent aftermarket ‘remanufacturing’ should feel the affect of the increased volumes.”

Joe Barrau, national sales manager, Tarani Rebuilders, says that he expects this to be the case, but with a caveat.

“This is truck country out here,” he says of Tarani’s Edmonton, Alta., surroundings. “We’re still seeing a lot of steering gear and steering boxes. Trucks do get put through more banging. Out here trucks are used for field service and they get put through more pounding. I suspect (rack and pinion) will be a bigger issue in the future. I just don’t think it has hit yet.”

One issue that he surmises will rear its head is the cost of repair.

“If a truck owner finds a vibration, is it really a motor mount or is it a rack problem? A lot of technicians do not like doing racks,” he says, adding that it can be a big job. “The customer is not going to be too thrilled either, because he was hoping for a $100 to $200 repair and is now looking at a much bigger one.” So, businesses are going to have to be prepared to sell the job to a truck owner who may have become accustomed to a bill of a different magnitude.

On the flip side, shops that become proficient at replacing racks can easily cut the by-the-book labor hours in half. Still, shops need to be on the lookout for rack failures and damage on vehicles that would traditionally have very robust parallel linkage designs.

Delphi’s Graham offers that the rack and pinion units on trucks are robust and designed for the job and should not be the subject of any higher degree of failures than normal. Yet, with the steering geometry such systems employ tending to put a lot of thrust energy into the inner tie rod ends, and urban drivers doing their best to put a good amount of thrust into curbs, damage to the racks, joints and bushings is inevitable.

But shops
need to look for it, and jobbers need to be prepared to service their information and parts needs when they see a unit they’re not familiar with.

“We’re probably a year or two from a major trend,” says Barrau, “but we’re certainly keeping our eye on it.”

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