A legacy lives on
The all-round drum brakes are from Meritor. Interestingly, to meet the latest braking distance requirement, these are big, big brakes – 16.5 x 5 Q Plus up front and 16.5 x 8.62 Q Plus on the tandem. A nice feature in the cab is the easy-clean vinyl ceiling and the sweep-out floor, making it a snap to keep the interior tidy. The steel cab is given a thorough rustproofing in the paint process, and the sleeper is a honeycomb-sandwich aluminum construction for light weight and corrosion resistance.
The windshield is split for inexpensive replacement. The tow hook is set in the middle of the slab bumper, where loads are distributed to both frame rails, rather than pulling on one.
On the road
Our route ran north on I-215 to the 138 cutoff to Pearblossom – down through the San Fernando Valley and back via Ontario to Perris and, finally, Fontana again. A second day brought our trip to 350 miles.
The run across to Perris was easy and showed the truck’s ride is not in any way compromised by its ruggedness. Once loaded, the ride was excellent, even with the fifth-wheel setting on the tandem centerline.
One thing that quickly became apparent was the light but precise steering. There have been significant advances with the steering gear, made by TRW Aftermarket, but at least some of the credit goes to the needle bearings – a feature of the Detroit front axle.
Other controls had the same quality feel, too: The dash is full of information with no fewer that 20 gauges, most visible through and around the adjustable steering wheel.
The wheel has none of the in-spoke switches with the exception of the cruise control. These switches are under the shift knob and, while the trend has been to put these on the steering wheel, their location on the shift lever is convenient and especially handy when hitting the resume button after a shift.
There was an obvious performance difference empty and loaded, though the 560 is a strong puller and excels in situations where you need a quick burst of power.
The fast throttle response and the extra boost from the turbo-compounding mean the engine builds torque far faster than competitive power. This is great for accelerating to speed on on-ramps for safe merging. It is also very useful when you need an extra boost to maintain momentum for short, sharp rises at freeway intersections, overpasses and such. It makes the Detroit engine feel much “bigger” and torquier than its rating suggests.
For the longer climbs, the DD15 just gets down and grunts, offering no complaint when lugging down to 1,100 or even 1,050 rpms. Again, the additional boost from the turbo-compounding helps, converting waste heat from the exhaust into useful work at the flywheel. Multiple injection events greatly reduce diesel knock, and the stiff crankcase of the new engines helps reduce noise. What noise does escape is suitably quieted by the insulation package that comes with the EX.
The tall final drive gearing meant some downshifting on the climb up Cajon and then across the Pearblossom Highway on the two-lane sections, but the easy-shifting 13-speed made it simple. In fact, the shift tower execution on the 4900 made it easy to select gears and a short throw to pick up each gear.
The combination of the compounding and the tall gearing contributes to fuel efficiency, where the DD engines have been proving themselves in the post-2010 emissions environment.