Tried and true

Steve Sturgess (Photos by Steve Sturgess) | March 01, 2012

Despite its relatively recent introduction, the Cascadia has reached an unassailable popularity on America’s highways. They’re so familiar you hardly ever think of the innovation that was introduced back in 2007. But it’s there, working in the background to make the Cascadia a reliable, durable and economical truck.


Powertrain detail

The Detroit DD15 was introduced late in 2007 to power the new Cascadia and Western Star trucks in North America.

The DD15 is an inline six cylinder featuring a common rail fuel system and turbo-compounded output that contributes up to 50 horsepower to the engine flywheel from waste heat in the exhaust stream. The turbo-compounding turbine has an inlet nozzle that converts the heat and pressure in the exhaust gas leaving the turbo to useful energy, while at the same time generating the backpressure needed for the EGR system to work. It drives the flywheel through gears and a fluid-filled clutch or coupling. In this way, it recovers energy normally wasted in a variable-geometry turbo system.

The DD15 covers power from 455-560 hp at 1,800 rpm. Torque ratings are 1,550-1,850 lb.-ft. at a nominal 1,100 rpm, with several multi-torque models offering 450 hp-1,550/1,750 lb.-ft. and 475 hp-1,650/1,850 lb.-ft. ratings.

The DD15 is recognized for its quiet operation. This is a consequence of the multi-event injection via the amplified common rail system, but it is also a result of less radiated combustion noise due to the rigid design on the cast iron block and the compacted graphite iron (CGI) one-piece head with its 38 clamping bolts.

The common rail is fed by a two-stage pump that is fully lubricated by the fuel. In its first compression, pressure rises to 900 bar before the secondary filtration. It then is raised to rail pressure of 2,100 bar. This pressure is amplified nearly four times inside each injector with a double-headed piston eliminating the need for external lines carrying extreme fuel pressures. Each electronically controlled fuel injection event has multiple pulses for precise control of fuel rate and shape, giving fine control of combustion and NOx generation.

In this application, the DD15 drives through an Eaton Solo clutch to a Fuller twin-countershaft FRO-16210C 10-speed transmission. The FR is a recently introduced transmission range offering a weight savings of 32 pounds over the RT series. The C ratio set has the broader gear spread for an overall reduction of 17.17-to-1. This transmission is an overdrive with a top gear ratio of 0.74-to-1.

The rear axle ratio is 3.42-to-1 and with the Goodyear G572 295/75R 22.5 drive tires turning 508 revolutions per mile, the theoretical engine speed is 1,286 rpm at 60 mph. Using the dashboard gauges, the truck appeared to be going around 1,260 rpm at 60 mph. That would be around 1,365 at 65 mph which is an excellent compromise between tall gearing for economy and a useful torque rise back to the engine’s peak torque at 1,100 rpm.


Freightliner Cascadia Specifications

Frame: Freightliner 11/32 inches thick by 3-1/2 inches by 10-3/16 inches steel, 120 ksi

Engine: Detroit DD15, 475 hp, 1,650 lb.-ft. torque

Engine Brake: Jacobs

Transmission: Eaton Fuller FRO16210C, 10-speed o/d

Wheelbase: 225 inches

Front axle: Detroit DA-F 12,000-pound dual taper-leaf suspension

Front tires: Goodyear G399 LHS 295/75R22.5

Rear axle: Detroit DA-RT-40 40,000-pounds, 3.42-1 ratio

Suspension: Freightliner Airliner 40,000-pound air-ride

Rear tires: Goodyear G572 LHD 295/75R22.5

Wheels: Accuride hub pilot, outside polished

Fuel tanks: Dual 120 gallons unpolished

DEF tank: 23 gallons

Fifth wheel: Holland FWS1

Seats: Freightliner Premium on swivels

Interior: Gray vinyl, premium lighting

Other: Freightliner heated, motorized mirrors; hood mirrors; roof fairing, skirts, side extenders; exterior sun visor; remote keyless entry; AM/FM/CD weatherband radio w/ iPod interface; automatic temperature control HVAC; daytime running lights; 160-amp alternator; Borg Warner on/off fan clutch; Delco 69MT starter; Davco 482 fuel/water separator; ConMet pre-set aluminum hubs; Virtual Technician diagnostics. strives to maintain an open forum for reader opinions. Click here to read our comment policy.