Dallas Smith, president, visits with Bill Hoover, VP-sales of Wabash National Corp. Dallas Smith is the exclusive national distributor of specialty high-cube trailers for Wabash National.
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Truck, Trailer Versions
Two versions of the DBX independent wheel suspension were displayed at a private showing of the new vehicles September 27 and 28 at the Indiana Convention Center in Indianapolis. The trailer version was shown under a typical household goods moving van or electronics van. The other, smaller version demonstrated how the DBX suspension could lower the floor height of delivery trucks.
Both versions of the suspension turn heads when they are driven on the highway. The Mayflower furniture van and the electronics van inspire a lot of questions on the CB radio waves because warehouseman vans are not often seen with three axles – or at least three single-wheel positions on each side. The low floor and smooth ride are highly visible to following trucks.
The small delivery van and the pickup are both standouts because of the tandem rear axles. The pickup - actually a cutdown Dodge Caravan minivan with tandem rear wheels independently suspended – was shown at the New York and Chicago auto shows earlier in the year. The one-of-a-kind truck attracted not only interest but also offers to purchase.
The suspensions in both the big trailers and small trucks are similar. Both have trailing arms that DBX Corp calls wheel plates. These are stabilized by tracking rods to reduce the castering forces. One air bag and one shock absorber cushion the ride at each wheel position. Stub axles are each fitted with a hub and brake drum and one standard-size tire.
Wabash National Alliance
The trailer suspension is going into production first. The exhibit in the Indiana Convention Center served two purposes: to introduce the new DBX independent wheel suspension and to announce a new alliance with Wabash National Corp of Lafayette, Indiana. Wabash National will build the DBX suspensions and will use them on a new line of warehouseman trailers introduced by Wabash. These trailers will be sold to the household goods moving industry by Wabash National Equipments Sales, a new dealership owned by DBX Corp. H. Lee Cox, vice-president and general manager of DBX was vice-president – maintenance at Mayflower Transit Inc for five years, and also had considerable experience at North American Van Lines Inc.
The first Wabash moving van with prototype independent wheel suspensions was built for Mayflower Transit. It will go into field-testing service at Mayflower in November after being refitted with the first of the production models of the DBX independent wheel bogie.
Production models will differ from the prototype by moving the Goodyear air spring. The 10” air bag will be moved from aft of the wheel to a position above the pivot bearing for the wheel plate in order to make room for individual brake chambers at each wheel. The original design used a single brake chamber with cables to all three of the slack adjusters. The new design has individual brake chambers each connected by a bellcrank and operating rod to the slack adjuster.
80” Between Wheels
This new design for the production suspensions will permit reducing the length of the wheel boxes by 20” on each side. Thus, the wheelhouse covering all three wheel positions will be 146 1/2” long and extend 51 1/2” above the road surface. The bottom of the suspension will be 9 1/4” above the road, and the floor framing will start at about the same height. The trailer floor height will then be about 15”.
The second critical dimension is the space between wheel boxes. “We want to get to a full 80 inches space between the wheels so we can easily drive a car between them,” says Dallas Smith DBX president. “Right now we’re at 77 to 78 inches, and it’s a little tight to get between the wheel wells. This is important because the majority of household goods moves include a car loaded in the van.”
That is one of the reasons Smith chose a tri-axle arrangement with standard low-profile tires. The trailer will have six Goodyear 255/70R22.5 tires. Dana’s Spicer Trailer Products Division is machining special spindles and brake spiders. Accuride Corp is forming a special wheel that will provide room for a Webb Hub and 161/2x5” drum. The bushings for the brake actuator are beefed up to compensate for the shorter S-cam shaft. The automatic slack adjuster is nested in a cutout in the wheel plate.
The wheel plates (trailing arms) of the prototypes were cast steel, but production models of the first run will be fabrications – starting with 1/14” steel plate. These trailing arms are stabilized against castering forces by tracking bars of 1” steel tubing extending to the trailer centerline. Pivot bushings of the wheel plates are of rubber in tension. These trialing arms are 22 1/2” long from pivot bushing to axle center, and the axles have 3” of travel up and 3” down.
To reduce tire scrubbing of the tridem in turns, an experimental magnetic sensor which is mounted in the upper coupler so that it can dump the air in the rear suspension. A lane change maneuver on the highway would not dump the air because the tractor fifth-wheel would not turn sufficiently relative to the upper coupler, but slow speed turns would trigger the sensor.
The air can be dumped manually at any wheel by pressing a switch. A cable winch above each wheel can lift the tire off the road. This feature would be used during empty backhauls or to move the trailer to a service station in case of a flat tire.
One of the trailers exhibited in Indianapolis was equipped with an auto ramp that in the up position is part of the rear trailer floor. When pivoted down to the ground by an electric cable winch, it provides easy access to drive a car aboard between the wheel wells.
Besides use as a car hauler and household goods or electronics van, the low-floor trailer has other applications transporting bakery goods and snack foods. With a 110-include inside height over the upper deck and a 32” drop to the rear floor, eave height at the rear would be close to 12 feet.
Straight Tuck Versions
The dropframe truck was developed because of interest that Mayflower officials showed in a transporter for storage boxes used in the household goods industry. These standard boxes measure 5 by 7 feet, 7 feet high. The 60” dimension would fit between the wheel boxes, and the floor would be low enough that a box could be rolled easily onto or off the truck.
The truck was later converted into a demonstration vehicle with clear plastic covering the wheel boxes. Riders seated inside the van body can see the movement of the suspension arms and tracking rods as the wheels roll smoothly over road irregularities. Air for the suspension is provided by an electric air compressor similar to that installed on a Chrysler Imperial.
Smith developed the pickup truck to explore other ways that a low-floor chassis might be used. The DBX suspension requires a front-wheel drive vehicle, which severely limits the number of chassis available. For the van and pickup, Smith chose a Dodge Caravan, which has front-wheel drive and monocoque body construction. The low floor in this pickup provides a cargo box depth of more than 33 inches. It has an electrically operated tailgate that functions as a ramp.
Another demonstration vehicle shows how a cab-and-chassis might look as it would be furnished to truck body builders. The base vehicle for this conversion is a Dodge Dakota midsize pickup with four-wheel-drive. The rear-wheel-drive is disconnected so that the vehicle is powered on the front axle only. While this conversion is satisfactory for demonstration purposes, Chrysler engineers say that for production chassis it would be better to use the 7.25-inch axle normally used for front-driving axles.
Other front-wheel-drive chassis are available, such as those developed to provide a low floor height in bakery delivery vehicles. For those delivery operations that need a low floor height, Smith says the DBX suspension provides a new dimension only inches above the road surface.
Necessity is the mother of invention, and Smith says that he first saw the need for an independent wheel suspension when he operated Dallas Smith Transport delivering cars and truck for General Motors dealers in four states of the Southwest. “We were always trying get one more car on the trailer, but we never could because the rear axles were in the way. I vowed then to build a suspension that didn’t need an axle. I’m no longer in the auto-hauling business, but now I have the suspension.” |
