General Motors has strengthened its 2009-model G-4500 chassis and increased its gross vehicle weight rating by 1,900 pounds and its towing capacity by as much as 2,400 pounds.

Upgrades to the cab, frame, suspensions, rear axle, radiator and transmission are among the changes allowing GVWR to go from 12,300 to 14,200 pounds. Sold as the Chevrolet Express and GMC Savana Van Cutaway, the chassis is used to mount cargo bodies as well as those for ambulances, school buses and motor homes.
Engineers redesigned portions of the G-4500's cab assembly for added strength. They added gusset-like reinforcers at key areas of the main frame rails, stiffening the rails so they can bear more weight. Stress analysis determined where to place the reinforcers, and they are welded on upper and lower flanges, in pairs facing each other. And the rails' kick-up area over the rear axle got an insert-like reinforcer for extra strength.
Rear spring assemblies were strengthened with reinforced shackles and hanger bolts to take more weight. Front and rear shock absorbers have new valving for better damping performance. The rear axle differential's housing, gears and tubes were beefed up while the brake rotors are thicker. And the parking brake assembly was redesigned to help dissipate heat.
The standard 4L85E Hydra-matic transmission was beefed up with a brazed torque converter turbine, induction-hardened turbine shaft, a 5-pinion reaction and output gear carriers, and an improved overrun roller clutch. A fluid cooler is mounted ahead of the radiator, which has greater cooling capacity. The 4-speed automatic is used with both the V-8s that power the G-4500, a 6-liter Vortec gasoline and 6.6-liter Duramax diesel.
Payload of the gasoline-engine '09 G-4500 cutaway chassis is 9,141 pounds and is the highest in this category, GM claims. The gas chassis' gross combination weight rating is 20,000 pounds, up from the '08 model's 17,600 pounds, while the '09 diesel-powered chassis' GCWR is 18,500 pounds.
Changes will be incorporated into the '09 vehicles during the model-year changeover this summer.