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Road Test: 2007 Dodge Ram Chassis Cab

Signs of Things To Come

G.R. Whale
May 30, 2007
The badge on the door reads "Ram 3500 Heavy Duty" with no mention of the chassis cab. The lack of a pickup bed makes the latter obvious, and since the text on the badge is similar to that of current pickups, it's safe to assume there'll be future badges on which the 3 becomes a 4 or 5 (see "Max Payload, page 10).
That the Chassis Cab 3500 may lead to heavier versions is a poorly kept secret. When was the last time you saw a mainstream vehicle with a platform that wasn't shared with something else? Besides, Chrysler doesn't have the funds to toss at new platforms. The medium-level commercial market sells about 100,000 units a year, easily large enough for Dodge to get a piece of that pie. Not only that, but Dodge wants to have something to offer to the guy whose trailer or business outgrows his Ram pickup, and a Sterling or Freightliner are too big. This chassis cab contains Dodge's other big news: the 6.7-liter ISB Cummins diesel. It's optional in this truck and in 2007 calendar year Rams, but they aren't identical engines.
Truck-body builders worry about only two things with cab and chassis setups: payload and ease of use. Its weight is about the same as a Ram pickup's because the sturdier components offset the lack of a pickup box. The Dodge rails are industry-standard C-channel beams 34 inches apart with little hanging off the sides except rear leaf perches and nothing--not even a vent tube--standing above the top of those rails.
Photo 2/11   |   2007 Dodge Ram Chassis Cab engine View
The large fuel tank is behind the axle, well skidplated and tapered up to the underside rail at the tail, so it shouldn't affect departure angle or drop platforms. Local delivery types who want more payload or to mount power equipment in the back (both transmissions offer a PTO) can opt for a 22-gallon tank inside the rails ahead of the axle in lieu of the big one.
The Chassis Cab comes as regular or Quad, though only the standard cab gives the choice of a 60 or 84-inch cab-to-axle length; fitting an eight-foot box onto a 60-inch Quad Cab is no problem, and fifth-wheel or gooseneck pullers shouldn't have clearance issues. With commercial design comes narrower-track dual rear wheels, four-wheel-drive models add a differential and axle shafts to the solid front axle, and max 23,000-pound GCWR means you can add a custom aluminum bed and pull a 15,000-pound trailer. Just as heavy-duty pickups have progressed to the point that driving them empty doesn't mean a punishing ride, these ride well with just one ton of bodywork over the rear axle, and the steering doesn't feel noticeably less communicative than on the independent front end.
Two reasons Brand F sells so many medium-duties are the pickup-truck cab that goes with Ford's models and lower height than most TopKick/Freightliner/Peterbilt-size trucks. To that end, you can get a Ram Chassis Cab with most of the luxo features available on Ram pickups, and little of that should change when a 4500 or 5500 series appears. Bigger springs, brakes, axles, and 19.5-inch wheels are easy to come by; there's no reason Dodge shouldn't offer them on the Chassis Cab.
The default engine for Ram Chassis Cab is the 330-horsepower Hemi with a G56 manual or five-speed automatic. The option is the Cummins ISB 6.7--at $5555, it's essentially the same price as the current ISB 5.9-liter diesel option. The larger capacity is driven by emissions, primarily to maintain the low-rpm torque characteristics, since fueling and turbocharging feed mid- and upper-rev output. It shares bore centers with the 5.9 and is no bigger externally, though the larger stroke required crankshaft-balance reprofiling to fit in the block and clear the skirts, and the cylinders have lost the water jacket between them; the 6.7 keeps the piston oil coolers, and the compression ratio's still healthy at 17.3:1. The architecture is similar to the ISB 5.9, but carryover is 40 percent or less.
Things have changed more on the outside, with watercooled EGR over the exhaust manifold, a MAP sensor and throttle on the intake horn, and a 14-vane variable-geometry turbocharger mounted a bit lower and further back. Also new are a layered oil pan, viscous vibration damper, and modified pulleys (including an overrunning alternator pulley so it doesn't squeal like a pig at shutdown), all designed to minimize NVH. Combined with the third-generation common-rail fuel system that handles multiple injection events per stroke, the larger engine is quieter than the one it replaced, keeps maintenance intervals and design life of 350,000 miles to overhaul, and weighs only slightly more.
Photo 6/11   |   2007 Dodge Ram Chassis Cab rear View
On the Chassis Cab, output is pegged at 305 horsepower at 3000 rpm and 610 pound-feet from 1600-2600. No clutch-engagement figure was quoted, but no one at Dodge disputed our assessment of nearly five inches of stroke giving "something more than 350-375 pound-feet." Don't fret if you were expecting more out of a larger engine. Since flat torque curves and operating economy are more important than horsepower to fleet operators and the G56 is limited in input capacity, torque took priority over a 20-horsepower drop from the pickup. This 6.7 is said to get better fuel economy than the 325/610 5.9. Look up any commercial engine, and you'll find top ratings reserved for fire apparatus and RVs, vehicles that seldom carry the engine's max load or only do so for limited intervals.
The electronic control of the VGT14 turbo can produce nozzle closure of 90 percent, doing the same thing as an exhaust brake. Therefore, for the first time, a factory exhaust brake is offered, and at $300 it's a lot cheaper than previous aftermarket units. The exhaust backpressure limit stays at 60 psi as does the maximum braking horsepower available (about 190), but from 2400 rpm down to 1000, the braking is better. The retarding effort of the VGT without the brake option is close to that offered on earlier models equipped with the "Ram Brake" exhaust brake.
On diesels with the six-speed automatic, the exhaust brake and powertrain controllers all cooperate, delivering automatic downshifts as the brake decreases speed to the next gear range. If on cruise control, the brake will operate to attempt to maintain the set speed on descents. The integration has brought an impressive setup, especially in light of the modest fee, and if you buy one secondhand that didn't come with the brake, we expect Mopar will offer a retrofit kit--it's mostly software and a switch below the climate control.
Aisin builds the commercial six-speed auto, a unit with a moderate first gear and two overdrives for relaxed highway miles. A glance at the 35-horsepower (max) PTO, big pan, and $2300 option tag, you can see this is real medium-duty stuff--and a stout 220-amp alternator is available as an option.

Dodge Ram 3500 Chassis Cab
Location of final assembly Saltillo, Mexico
Body style 2- or 4-door cab and chassis
EPA size class Medium heavy-duty
Drivetrain layout Front engine, 2WD/4WD
Airbags Front
Base engine 90° V-8, iron block, alum heads
Bore x stroke, in 3.92 x 3.58
Displacement, ci/L 343/5.7
Compression ratio 9.6:1
Valve gear OHV, 2 valves/cyl
Fuel induction SFI
SAE horsepower, hp @ rpm 330 @ 5400
SAE torque, lb-ft @ rpm 375 @ 4200
Opt engine I-6 turbodiesel, iron block/head
Bore x stroke, in 4.21 x 4.88
Displacement, ci/L 408/6.7
Compression ratio 17.3:1
Valve gear OHV, 4 valves/cyl
Fuel induction Common rail
SAE horsepower, hp @ rpm 305 @ 3000
SAE torque, lb-ft @ rpm 610 @ 1600
Base transmission 6-speed manual
1st 5.94:1
2nd 3.28:1
3rd 1.98:1
4th 1.30:1
5th 1.00:1
6th 0.74:1
Reverse 5.42:1
Axle ratios 3.73:1, 4.10:1
Final drive ratio (w/3.73:1 axle) 2.76:1
Opt transmission 5-speed automatic
1st 3.00:1
2nd 1.67/1.50:1
3rd 1.00:1
4th 0.75:1
5th 0.67:1
Reverse 3.00:1
Axle ratios 3.73:1, 4.10:1
Final drive ratio (w/3.73:1 axle) 2.50:1
Opt transmission 6-speed automatic
1st 3.74:1
2nd 1.96:1
3rd 1.34:1
4th 1.00:1
5th 0.77:1
6th 0.63:1
Reverse 3.54:1
Axle ratios 3.73:1, 4.10:1
Final drive ratio (w/3.73:1 axle) 2.42:1
Transfer-case modelNV271, NV273 p/t 2-speed
Recommended fuel Midgrade unleaded, ULSD
Wheelbase, in 143.5, 163.5, 167.5
Length, in 234.3, 254.3, 258.3
Width, in 79.5
Height, in 78.6-79.1
Track, f/r, in 68.7-69.6/68.1-71.7
Headroom, f/r, in 40.8/40.0
Legroom, f/r, in 41.0/36.7
Shoulder room, f/r, in 67.0/66.5
App/dep/brk angle, deg 24.5-24.9/21.5-22.0/20.4-22.0
Base curb weight, lb 5784-7290

Pickup Power?
For the Ram pickup, the 6.7 carries ratings of 350 horsepower at 3000 rpm and torque of 650 pound-feet at 1500 if you choose the automatic; torque drops to 610 at 1400 with the six-speed manual. Different emissions certifications and duty cycles are the primary reasons, plus cooling requirements, gearbox input capacity, and the 16-vane VGT on the pickup version. It's approved for B5 fuel and claimed to be 50-percent quieter (remember, sound scales aren't linear), yielding a 3dBA reduction to interior noise levels, and the muffler is beyond any emissions component, so you can take it off if it's too quiet.
Photo 10/11   |   2007 Dodge Ram Chassis Cab side View
Pickups get a Chrysler six-speed automatic, dubbed 68RFE, with a quoted best-in-class gear ratio spread of 5.16:1. Like the Aisin box it has two overdrives, with the Aisin using a much deeper first and the Chrysler box a much shorter reverse ratio. The ISB 6.7 and 68RFE appear in Ram pickups built after January 1, 2007, and pricing hadn't been announced as of press time.--GRW
Photo 11/11   |   2007 Dodge Ram Chassis Cab front View



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