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It was once common to see cabover rigs towering high over American highways. But today, cabovers are as scarce as $1 per gallon diesel.
What happened?
Federal laws restricting the overall length of tractor-trailer combinations were relaxed in the 1980s, and as a result, trucking companies and operators fled to conventional cabs. Common complaints from drivers about cabover trucks included a harsher ride from sitting over the front axle, increased noise and heat from the engine occupying so much of the cabin, the inconvenience of having to jack the cab to access the engine and a lack of usable interior space.
Later cabover designs (like the football-helmet shaped Peterbilt 372) incorporated aerodynamic tricks to make these flying barn doors slip through the wind, but it's far easier to design conventionally styled cabs with a lower drag coefficient--which translates into increased fuel mileage for operators. Yet another nail in the cabover's coffin.
One major U.S. truckmaker reported a 90 percent drop in sales of cabover road tractors in the 10-year period from 1988-'98 and, by the middle of the last decade, the cabover design had all but disappeared from U.S. truck dealer showrooms. Most cabovers sold today are light delivery trucks, garbage trucks and fire trucks.
The GMC Astro cabover was a casualty not of the sudden trend toward conventional cabs, but of GMC's flagging heavy-duty truck sales in the middle of the 1980s. By 1987, GMC had merged its heavy-duty truck line with Volvo, forming WhiteGMC, which was discontinued by Volvo in 1995. The GMC Astro was phased out prior to the merger and last built in 1987, ending a nearly two-decade run that began in 1968 as a 1969 model.
The Astro was largely unchanged, and definitely showing its age when it was killed off, but in the mid-1960s, forward-thinking GM engineers put a great deal of effort into making the box-shaped cab as aerodynamic and comfortable as possible.
Aero testing of the Astro cab began in 1965, using scale models at the Harrison Wind Tunnel at the GM Technical Center in Warren, Michigan. The truck's greenhouse was tweaked, angled and sloped to create a streamlined airflow over and around the cab. In 1976, a "Dragfoiler" was tested on the Astro's roof to improve airflow over van trailers that were higher than the top of the truck's cab. The Dragfoiler reduced drag by a whopping 34 percent, which translated into a virtual 34-horsepower advantage.
Wind-tunnel testing showed that without the Dragfoiler, air would break over the top of the Astro's cab and nosedive into the area between the truck and the trailer, putting additional resistance on the drivetrain. But with the Dragfoiler on the roof, air would ramp up and over the top of the van trailer, minimizing drag.
Visibility was also a major consideration when the Astro was designed, so the truck was given 2,821 square inches of windshield area--the largest of any American-made truck at the time--as well as ultra-thin windshield corner posts. The driver of an Astro had a panoramic view of the road, but also an unimpeded view of low-lying obstacles when negotiating in tight quarters. From the driver's seat of an Astro, it is possible to see objects as low as 50 inches high, and as close as 40 inches from the front bumper. Looking out the right side window, objects as low as 40 inches high and as close as three feet from the truck are visible.
To ensure driver comfort inside the cab, designers first made clay and fiberglass bucks of the Astro's control panels in order to make certain that all gauges and switchgear fell within easy reach. A bank of gauges to the driver's right was designed so that each gauge and gauge needle lined up, allowing the driver to spot a problem at a glance. By the 1980s, Astro interior offerings had become increasingly luxurious as GM struggled to compete with rivals. The top-of-the-line Royal Classic interior offered knit fabric upholstery and wall-to-wall carpeting. Standard interior trim in the Astro was more primitive, with rubber floormats, vinyl headliner and upholstery.
GMC Astro cabs were built almost entirely out of aluminum, with SMC fiberglass-reinforced plastic doors, and were offered in three lengths: the short 55-inch non-sleeper cab, a 75-inch sleeper cab and an 87-inch sleeper cab.
Near the end of its run, Astro buyers had the option of several Detroit, Caterpillar and Cummins Diesel engines. By the 1980s, Detroit two-cycle diesel engines were a dated design, but the 290-hp 6V-92TTA Fuel Squeezer Plus was the standard engine in the Astro. (A word about Detroit engine nomenclature: The 6V meant the engine was a V-6, the 92 stood for 92 cubic inches per cylinder and the TTA designated a turbocharger/aftercooler system.) Buyers could also opt for a Detroit Diesel 8V-71 or a 414-hp 8V-92.
New for 1982, Cummins offered its 855-cu.in. straight-six Big Cam II series engines in 300-hp, 350-hp and 400-hp varieties. Less powerful Formula 300 and 350 Cummins engines were available as well.
The rugged 14.6-liter Caterpillar 3406 was also offered in the Astro on tandem axle models. The 3406 was a giant at 893 cubic inches, and was offered in a variety of horsepower ratings starting at 278 hp at 1,900 RPM.
The Astro also served as one of GM's test beds for gas turbine engines from 1970-'75. The turbine project never reached production, however, due to its high build costs and the engine's thirst for fuel--especially when compared alongside diesel engines.
The standard transmission on the Astro was an Eaton Fuller nine-speed Roadranger, but a variety of other transmissions were available. The standard axle ratio was 3.70:1.
Single-axle Astros came standard with a 23,000-pound Eaton axle with leaf springs. Tandem axle trucks could upgrade to GMC Astro-Aire air suspension, Reyco suspension or Hendrickson suspension. The standard axle used on tandem trucks was a 34,000-pound Rockwell, and suspension capacities could range from 34,000 pounds up to 65,000 pounds, depending on configuration.
Astros could be ordered from GM as a "glider" as well--essentially a painted, finished cab mounted on a frame with a front axle--allowing the owner to install his choice of engine, transmission, suspension and rears.
The age of the cabover semi truck in the U.S. may indeed be in the rearview mirror, but enthusiasts are keeping trucks like the Astro alive and well on the Internet and at commercial truck shows. They're popular with modelers and kit builders, too--especially the AMT kit that includes the experimental gas turbine engine. These can be found selling for anywhere between $50-$100.
SPECIFICATIONS
Engine: 6V-92TTA "Fuel Squeezer Plus" two-cycle, six-cylinder turbo diesel, displacing 552-cu.in.
Horsepower: 290 @ 1,900 RPM
Torque: 957-lb.ft. @ 1,300 RPM
Transmission: Fuller RT-11609A, nine-speed
Final drive ratio: 3.70:1
Front axle: 12,000-lb standard/18,000-lb. optional
Rear axles: Rockwell SLHD standard on tandems with 34,000-lb. Reyco 101 A suspension
Price today: $6,000-$10,000
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The latest electric-only F-150 Lightning is certainly a quick vehicle in its own right, but this 2001 edition from the engineers at SVT was built for excitement, not range. It was made with an old-school muscle-car vibe along with modern handling and braking. Which Lightning would you look good behind the wheel of?
Take a look at this second-gen Lightning on Hemmings Auctions before the bidding ends.
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