In the transition to Tier 2 emissions compliance, Caterpillar matched performance of the new Cat 3512C HD engine powering the 150-ton mechanical-drive 785D to that of the rigid-frame haul truck’s predecessor, making the 785D a drop-in replacement for mines using the 785C. Along with component commonality to make the transition easier for mine managers, Cat upgraded the rear-axle filtration and brake friction disks to make the standard model run more cost effectively.
Cat claims the 3512C HD (high-displacement) engine retains the fuel efficiency of the short-stroke 3512B engine it replaces, making 1,348 net horsepower at 1,750 rpm just like the 3512B. The high-displacement engine demonstrates 12 percent better brake mean effective pressure than the 3512B, which the senior marketing rep for mining trucks, Jeff Taylor, says is an indicator that the engine is generating the power without working as hard. The new engine complies with U.S. EPA Tier 2 emissions standards, and Cat says it operates at altitudes up to 14,000 feet without derate.
The dual-slope body standard on the 785D offers the same capacity as the 785C; but the new truck weighs nearly 1.5 tons more than its predecessor. With gross vehicle weight capped at 550,000 pounds, the 785D has a nominal payload about 1.5 tons less than the 785C.
Caterpillar also introduced the X body as an option with the 785D. The new body provides more volume – 111 cubic yards compared to the dual-slope body’s 102 cubic yards. The Mine Specific Body (MSD II) and gateless coal body are also choices. The canopy of each of the bodies extends farther to protect the cab better.
The 785D has improved catwalks and a 600-millimeter diagonal stair.
Caterpillar aimed to improve rear-axle life by upgrading filtration on the 785’s rear axle lube. A hydraulic pump runs independent of ground speed, and continuous flow through the 6-micron filter is intended to maintain ISO 18/15 cleanliness. Lubricant volume supplied to the differential is increased, especially on an uphill grade when the axle is working the hardest. Cat says the improved cleanliness and lubrication should slow component wear, improving power train life.
Caterpillar also made its extended-life brake friction material – a popular option on mining trucks – standard equipment on the 785D. Cat says the glazing-resistant discs can last twice as long as standard brakes. And radial-seal air filters, which have proven to keep more contaminant out of other Cat equipment over the years, replace wing-nut-retained filters.