Underneath the familiar sheetmetal is a vastly improved truck
Car and truck manufacturers have a habit of making improvements from the outside in. General Motors broke that habit with the 2011 Chevrolet and GMC Silverado and Sierra HD trucks by offering a long list of foundational technical improvements without many visual ones. On the outside, the '11 HDs get little more than a grille change and minor styling upgrades that you have to look at twice to notice. But what's newsworthy about the new HDs is what's lurking beneath the sheetmetal.
We were invited to spend a couple of days in the hills of Maryland, Pennsylvania and West Virginia to use the '11 HD Chevrolets and GMCs as you might: Loaded to the gills. Some of the trucks were carrying payloads of 1,800 or 3,000 pounds. Others were hitched to conventional camp trailers weighing over 9,000 pounds. One lugged a 12,800-pound fifth-wheel horse trailer. Another had 10,500 pounds of equipment trailer and skid steer hooked up.
The major technical changes start skeletally. The HDs get a completely new, fully boxed chassis that's much stiffer torsionally than the '10s, and the upgrade allowed for a complete redo of the suspension. Though the IFS is similar in general design to the previous SLA (Short/Long Arm) system, the components are all new and heavily beefed up. The upper control arms are now forged steel, with the lowers of cast iron. There are now five torsion-bar rates, fitted according to the rated front Gross Axle Weight Rating (GAWR) of the truck. The maximum front GAWR has increased 25 percent from a previous maximum of 4,860 pounds to 6,000 pounds-something that will make the snowplow crowd happy. The steering system was revamped, with a considerably faster steering box ratio that delivers better road feel and fewer turns lock-to-lock, all with no increase in steering effort.
Gone is the long-running two-piece front diff housing, replaced by a one-piece Salisbury design that is 7-percent stronger. Additional front drivetrain strength was gained with improvements in the CV axles, which were upgraded from six- to eight-bolt inner flanges, and the outer stubs are larger for a 22-percent improvement in strength. The brakes grew substantially, from 12.9-inch discs to whopping 14-inchers at both ends.
The rear axle and suspension weren't ignored, with the GAWR of the AAM 11.5-inch axle rising from 8,200 to 9,750 pounds by upgrading the axle tubes from 3.5- to 4-inch diameters. Axletube diameter was increased 11 percent in the diesel-powered trucks. The rear springs were upgraded from 2.5- to 3-inch width and are asymmetrical (meaning the axle mounts forward of the spring center). This reduces spring wrap, both empty and loaded. The diesel trucks come only with a 3.73:1 axle ratios, but the gassers have a 4.10:1 option.
The proven Duramax engine, an $8,395 option, picks up a boodle of power and torque for 2011. It goes from 365 to 397 horsepower and from 660 lb-ft to 765 lb-ft. According to Gary Arvin, the Duramax Diesel Chief Engineer, there's room to grow from there. The Duramax's Allison 1000 trans is still a six-speed, but the internals have been heavily revised to deliver a commercial-grade duty cycle without the commercial-grade "neck-snapper" shifts.
The standard engine for the HD is the still silky 6.0L flex-fuel Vortec V8. Yeah, it's riding on the coattails of last year's upgrades, cranking out 360 horsepower and 380 lb-ft, but that's a good thing. It's a potent, economical engine and more than enough for a 3/4-ton or 1-ton truck. Its superb performance is why we don't miss the old 8.1L big-block any more than we do. Several of the trucks at the event had 6.0L V-8s and they had plenty of go, whether loaded or unloaded. It's matched well with the 6L90 six-speed automatic that has a nice, deep 4.03:1 first gear.