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Truck Topics

General Motors New Medium Duty Trucks Offer New Designs And Innovations

By Lee Kurtzmann
Posted Apr 4th 2002 9:25AM

Back in the "early" days of expediting, there was a wide variety of truck makes utilized in this business. It was common to see expediting owner/operators using Internationals, Fords, UD COE's, Mercedes and other makes no longer considered to be expediting material.

Two other makes that were among the most popular choices for Class 6 and 7 trucks were the Chevrolet /GMC - Top Kick/Kodiak models. As the 1990's progressed however, the Freightliner FL 60's, 70's and 80's developed as the primary expediting trucks, and the other makes receded in popularity as an expediting straight truck platform.

But that was then, this is now.

General Motors is once again entering the medium-duty fray and it looks like they have every intention of regaining their market share. Code named "GMT560", the introduction of their new medium-duty(for our purposes, Class 6-8) series of trucks, is the next step in claiming more of the work truck market. It will be introduced during the first half of 2002 as early 2003-model entries.

"Our new medium duty truck lineup showcases GM's continued focus on the commercial side of the business with products that offer high levels of productivity and efficiency," said David A. Hansen, general manager, GM Fleet and Commercial Operations.

"Operators will love the ride, handling, superior visibility, outstanding maneuverability, along with all the comfort and safety features we've designed into this family of trucks."

After more than $500 million of production facility renovations, the assembly plant in Flint, Michigan will become GM's new core commercial truck manufacturing center. These renovations include 30,000 square feet of added manufacturing floor space, and 12 new final assembly inspection bays.

The Janesville, Wisconsin plant will continue building previous generation medium duty trucks into the third quarter of calendar year 2002.

GM says that new state-of-the-art equipment and machinery and the best practices and processes of GM's light-duty truck plants are being used to produce the new GMT560 line. Some 80 percent of the operations in Flint's new body shop, for example, are automated, with robotics providing consistently high quality, cab-to-cab applications of welds and sealants.

The new trucks also have a high degree of parts commonality, which simplifies assembly and enhances quality. Many former regular production options (RPO) and special equipment options (SEO) are now standard.

Also, more than 200 of the SEOs, cited by customers as most important to them, have been converted to RPOs.

The GMT560 is a totally new design family, which includes an aerodynamic tilt-hood and cab sheet metal, wider front wheel stance for improved stability, and stronger industry standard frames with a "clean back-of-the-cab" design that will not interfere with a body install.

All earlier GM medium-duty trucks borrowed the cab sheet metal from the company's light-truck line. The GMT560 cabs were designed specifically for this market. In addition to the roomier cabs, the new sloping front hood improves forward visibility.

New C6500, C7500 and C8500 (Class 6-8) Series trucks, replacing GM's C-Series conventional cabs, will be initially available in two-wheel-drive regular cab, commercial cutaway chassis cab and crew cab.

Their GVWRs, ranging from 19,501 to 61,000 pounds, provide enough muscle to handily compete in the lower-end of the Class 8 heavy-duty segment, claims GM. Models include LoPro, Tandem and Tractor variants.


The new 7800 six-cylinder diesel joins the premium Caterpillar 3126E in the C6500/7500/8500 in-line diesel lineup. The Duramax engine is designed for durability and low operating costs.

The Duramax 7800 has a best-in-class 410,000-mile B10 durability rating, based on 90 percent of the engines operating at least 410,000 miles, without requiring major servicing.

All of its maximum horsepower ratings are available at the same 2200 rpm and its maximum torque ratings at the same 1450 rpm, including:

200 hp and 520 lb-ft of torque
215 hp and 605 lb-ft of torque
230 hp and 660 lb-ft of torque
250 hp and 660 lb-ft of torque
250 hp and 800 lb-ft of torque
275 hp and 800 lb-ft of torque
275 hp and 860 lb-ft of torque

The Caterpillar 3126E provides more service-oriented features and benefits, operates more cleanly and offers an expanded range of 11 power ratings. All torque ratings are available at 1440 rpm. Choices include:

190 hp @ 2500 rpm and 420 lb-ft of torque
207 hp @ 2500 rpm and 520 lb-ft of torque
210 hp @ 2500 rpm and 520 lb-ft of torque
210 hp @ 2500 rpm and 605 lb-ft of torque
230 hp @ 2400 rpm and 660 lb-ft of torque
250 hp @ 2400 rpm and 660 lb-ft of torque
250 hp @ 2400 rpm and 800 lb-ft of torque
275 hp @ 2400 rpm and 800 lb-ft of torque
275 hp @ 2400 rpm and 860 lb-ft of torque
300 hp @ 2400 rpm and 800 lb-ft of torque
300 hp @ 2400 rpm and 860 lb-ft of torque

Allison 2000 Series transmissions are standard in GM's C6500/7500 Series; the Allison MD 3000 Series is standard in the C8500 single-and tandem-axle models.

Optional manual transmissions include a range of Eaton 5-, 6-, 9- and 10-speed models and two TTC 7-speed models.


GMT560s share a stamped, straight section, C-channel frame design, providing maximum strength and a clean back-of-cab design for easy, low-cost body and equipment installations.

C6500/C7500/C8500 models also use larger-sized frames and offer a wider selection of wheelbases to accommodate larger-sized bodies. The longest 296-inch wheelbase single-axle and 308-inch wheelbase tandem axle models, for example, are built on a 450-inch frame, which is 80 inches longer than previous model offerings.

Single-axle models can easily accommodate bodies up to 30 feet in length, without requiring any extra-cost frame extensions.


C7500 models (with up to 33,000-lbs GVWR) feature a new standard hydraulic four-wheel anti-lock disc brake system, with standard four-channel ABS, Electronic Brake Distribution and available traction control.

C6500-C8500 models have a low-drag, four-piston opposed piston, fixed caliper brake design, with diameters sized to particular GVW/load requirements. Premium, high-capacity, 70mm , 4-piston brake systems are now standard on both the front and rear.

Twin-piston brakes feature a new pin-sliding design. Heavier models, rated at 19,500-lb GVWR and up, feature a new "totally fixed mount" caliper design.

Both brake designs reduce wear, corrosion and potential caliper binding by separating the function of moving the caliper from that of applying actual clamping force to stop the truck. The new non-asbestos brake linings last up to twice as long.

Depending on the required capacity, the brakes use either a HydroBoostâ„¢ or HydroMaxâ„¢ brake booster for their actuation. Both operate on the same principle, with the power steering pump supplying the booster power.

A tandem (split) master cylinder provides the independent front and rear circuits for the hydraulic brake system. Sensors warn the driver of "low fluid" or secondary brake failure.

Electronic Brake Distribution optimizes front-to-rear braking balance and control by detecting minute changes in wheel speed and limiting the amount of rear brake pressure to prevent impending wheel lockup, without activating the ABS.

Four-channel ABS minimizes stopping distance under certain conditions and improves control on slippery surfaces.

The traction control system, available for the first time, is amazingly effective in improving acceleration and vehicle stability on slippery surfaces by minimizing wheel spin.

The system uses the ABS brake system to control wheel spin – allowing the driver to retain full engine control and acceleration.

C6500-C8500 models also offer air drum brakes, which now include a standard bobtail relay valve for tractors and standard air dryers on all models.


GMT560 models use a new steering geometry, including high inside turn angles, longer front suspension springs and a slightly set-back front axle to provide improved maneuverability, says GM.

Class 6-8 models, like the C6500 with a 152-inch wheelbase and 84-inch CA, also outmaneuver major competitors. The C6500's 39.0-foot turning diameter is 4.2 feet shorter than a 150-inch wheelbase Freightliner with the same CA.

Virtually all models use wider 80- to 82-inch front tracks, permitting wheel cuts of up to 54 degrees, to create their increased maneuverability. The track widths also provide more stability.

GM says that a larger cross section beam with greater strength and stiffness enhances straight-line steering direction and control when the brakes are sharply applied.

Longer front spring suspensions and new steering linkages, including longer drag links, pittman arms and a longer steering arm, accommodate the front axle's slightly setback position and improved turn angles.

Front springs, up to 100mm long, typically extend over four inches further out beyond the front axle than previous generation models. Frame lengths have also been increased to provide more overhang for spring attachment.

All GMT560 models feature the new ZF S-2 steering gear, providing the segment's highest output torque-to-weight ratios and improved durability. Standard variable ratio steering is featured, as part of its more efficient and durable integral recirculating ball design.

The variable ratios improve on-center performance and provide additional power assist at higher turn angles to help increase maneuverability.

A complete redesign and retuning of the steering systems from the steering gear through the axle and tires also provides improved on-center feel, with what GM describes as effortless tracking on the highway and which minimizes the steering correction required on rough roads and in harsh terrain.

GM engineers created a new ride metric test and benchmarked all types of vehicles against it. Ride metrics measures sensory feedback at every point the driver contacts the truck, such as the seat, steering wheel and floor.

The test even measures such items as the truck's effect on side-to-side head movement.

Ride quality

The C6500-C8500 have a unique, new three-point cab mounting system, which incorporates a specially designed "bridge support" at the rear for extra isolation. It uses a very large body mounting bracket, almost like a crossmember, with "legs" that attach to brackets on the front. At the center of the "bridge," a cushion sandwiches each bracket.

Newly available uplevel Hystec™ cab mounts on all models optimize comfort by effectively isolating the cab in all directions and helping dampen the ride. The Hystec™ mounts attach at the front and are filled with stacked-up plastic discs, sitting in lubrication, which allow GM engineers to adjust them – in effect, "tuning" the damping of the mount.

A full range of tires are available to further enhance ride quality.


C6500, C7500 and C8500 models, with slightly higher frames and cabs, also provide increased 18.8-foot forward visibility. A lower-height instrument panel in all models ensures even shorter drivers of a full road view.

All GMT560 models feature a 25-percent larger windshield, with longer adjustable intermittent wipers, a large, full-width fixed back panel window and optional full-width, sliding rear window with three panes. All windows have standard Solar Rayâ„¢ tint.

Larger, standard integral, convex outside mirrors improve rearward visibility. GM tells us that their aerodynamic, foldaway design (both forward and rearward) also minimizes wind noise for more cab comfort and reduces potential repair costs.

Electrically heated, lighted or heated, lighted and powered mirrors are optionally available. Both left- and right-side power mirrors provide four-directional adjustment. The new single arm mirrors are mounted to the structure cowl, eliminating the armed door attachments.

Cab design

GM says that their new cabs provide more room and outstanding comfort and functionality by blending the operator friendly feel and easy-to-use controls functionality of light-duty trucks with the functionality of a true medium-duty design. The regular cab offers flexible seating for one, two or three passengers.

A full range of seating options is available, including driver and front passenger air suspension seats for optimum comfort.

The cabs are quieter, with a 50-percent reduction in noise, vibration and harshness (NVH). Powerful climate control systems are capable of heating and cooling cabs twice their size.

A range of high-quality Delco audio systems and amenities like large cup holders provide additional comfort and convenience.

The GMT560's offer a standard driver and available passenger side air bag to enhance safety. The center of the uniquely designed instrument panel (IP) curves out and angles towards the driver, providing a direct view of controls and gauges with a slight turn of the head.

The IP also features up to 24 telltale warning lights and gauges and places them within closer view and easier reach of the driver for added safety.

The new cabs provide flexible storage. The entire two-passenger front seat lower cushion can also be propped up to provide a large storage container. Two-piece floor storage trays are located behind the front seats and storage pockets in both sides of the front doors.

An additional storage area compartment, with a hinged locking door, is available in the step well.

Additional functionality comes from two 12-volt power points on the IP, along with a cigarette lighter and a power point in the center console. Lower step-in heights, generously sized tread plates, and convenient assist handles also provide easy vehicle entry and egress.


GMT560 products improve on the current C-Series models, which already provide the least amount of unscheduled downtime, according to J.D. Power, with even higher reliability/durability.

Cabs feature a high-gloss exterior finish, provided by GM's high quality basecoat/clearcoat electrocoating paint process, which GM claims makes the paint more resistant to fading and chipping and helps prevent corrosion.

The upgraded electrical system, while maximizing the power of the onboard computers, increases reliability/durability for operating systems by reducing potential problem sources and providing more diagnostic capability. GM says that this design uses fewer electronic control modules to do more work.

The system also takes greater advantage of Class II multiplexing technology to eliminate over 20 percent of the previously required wires, relays and splices.

The unique design and integration of components into major modules within the engine compartment allow layers of parts to be removed, providing a major enhancement to serviceability.

Four major modules are layered, so a service technician can strip them off in a more efficient manner independently or in sequence, depending on the amount of accessibility required.

It looks like General Motors has been burning the midnight oil in redesigning this series of trucks. With a scheduled release date of sometime before mid-year, the trucks will undoubtedly be accepted by those Chevy/GMC fans or dedicated users in various fields, and then in fleet sales.

Whether the GMT560 gains acceptance with the expediting owner/operator remains to be seen. It does however, represent an alternative for the buyer and that's a good thing, right?

Web Information
GMC Commercial Series Web Page


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