Stopping power was adequate for the payload, but we’ve got a gripe that GM needs to equip these trucks with larger diameter disc brakes.
At 12.8-inches front and rear, they’re smaller than the standard 13.9(!) and 13.6-inch discs on the all new light duty 2007 Toyota Tundra. We’d like some extra meat for this barbecue if we’re going to be pushing payload limits and need to brake suddenly.
GM offers two distinct dashboards for its new pickups.
The Sierra, clothed in SLE trim, featured the “pure pickup” interior that traditionalists like us love. It’s what a truck dash should be. Functional with large buttons and great ergonomics, the recessed and silver bezzeled analog instruments look terrific and instantly provide the driver with critical information from trailering braking power levels to fuel economy. The texture and grain of the truck dash is much better than the 800s. Gaps are crazy tight. Clearly Bob Lutz’s attention to vehicle interiors has been heard and buyers are going to be rewarded even on the Work Truck level trim.
Truck number two was a Sierra 3500HD single rear wheel crew cab long box equipped with a Duramax diesel. With an empty bed, it was an oil burning hot rod.
The latest edition of the proven Duramax is the 6.6-liter V8 LMM. Like the 2007 Ford Super Duty's Powerstroke and the Dodge Ram's Cummins, this diesel is pushing the envelope when it comes to performance and emissions.
January 1, 2007 the federal government ratcheted up emissions rules for diesel engines to reduce particulate emissions by 90% and nitrogen oxide output by 50%. The feds also mandated the sale of ultra low sulfur diesel (ULSD), which reduced sulfur content in diesel fuel from 500 ppm to 15 ppm.
To meet the tough new rules, the LMM differs from the previous LBZ version by adding a complex diesel particulate filter (DPF) to scrub the exhaust gases and a larger exhaust gas recirculation (EGR) cooler to lower cylinder temperatures and reduce nitrogen oxide during combustion.
The new DPF system is particularly interesting. It’s a “regenerating” multi-stage filter that passes engine exhaust into a ceramic, honeycombed block, trapping the particulates after they’ve passed through an oxidizing catalyst. Sensors before and after the emissions system tell the DPF when there's too much back pressure from the soot load. To clean the filter the engine temperature is briefly raised to 1,022 degrees Fahrenheit to incinerate the trapped particles, thus regenerating the system for another round of filtering.
While great for emissions, if you regenerate immediately after a fuel stop, you’re going to be disappointed with the fuel economy even though overall fuel economy for the LMM is expected to be slightly better than the LBZ.