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First Drive Dodge Ram T-Rex: Real-world 6x6 with A 26,000-Pound GCWR

Posted in Vehicle Reviews on July 1, 1997 Comment (0)
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First Drive Dodge Ram T-Rex: Real-world 6x6 with A 26,000-Pound GCWR
Photographers: Greg Grasmehr

Sometimes, to see the future, you have to look into the past. And when the concept team at Chrysler was given the go-ahead for a 6x6 full-size Dodge Ram, they went all the way back to the Jurassic Age . . . to create "T-Rex'' (Technology Research Experimental vehicle). "We wanted to make something no one could turn away from," said Leon Dong, manager of Advanced Chassis & Drivetrain for Dodge Truck. "But we also wanted to make something to exist in the real world-something that could eventually get made."

That may sound strange, but given the number of freaky concept vehicles at the different auto shows, this particular attitude is refreshing. Leon and the team were given the problem in August 1995, and told they needed to have the working solution in 14 months. Needless to say, they scrambled.

Tall And Mean
The T-Rex is founded on a 133-inch regular-cab 1-ton chassis with the front half of the frame being identical to a standard Ram; however, the back half of the frame is fully boxed and dead straight (no bends to allow for dual rear wheels are necessary). With three working axles, the chassis design took some thought.

The heart of the suspension system is a Delphi-engineered air-spring setup originally designed as an option for the Grand Cherokee. The bags, compressors, and sensors seem ideally suited to handle full-size truck payloads and heavy-duty work cycles. Both shocks and the bags themselves can be specifically tuned by the driver to accommodate rocky trail exploring, fifth-wheel long-distance hauling, or everyday cruises to work.

Two huge crossmembers under the 8.5-foot bed support the air suspension's air bags, one at each wheel. The six Firestone-designed air springs were used by Delphi Chassis (formerly a division of General Motors, now an independent contractor) to suspend the full-full-size truck weight. The springs are damped by six dual-rate adjustable shocks, which control the front and dual rear Dana 60 motions. Delphi designed the computer and electronics for the suspension with individual sensors on both air bags and shocks to provide input about load leveling and shock rebound speeds. Four vehicle position sensors-two near the front axle, two on the frame above the third-also keep the computer informed, while input from the brake system, speedometer, and dash-mounted manual switches are constantly monitored as well.

With all these sensors, the suspension can be adjusted to any degree preferred. A control switch adjusts shock valving between "Comfort" and "Sport," while a five-position dial allows for close to six inches of adjustable ride height: Max Off Road, Off Road, Auto Adjust, Entry, and Disable.

There are four load-leveling sensors that continually monitor each corner of T-Rex. Input is fed to the central computer, where minute adjustments can be made within milliseconds. The Delphi system isn't tuned specifically for everyday highway duty, but offers the options of higher payloads and "driver-decide" chassis control.

"Max Off Road" raises the air bags approximately 3.5 inches from the "Auto Adjust" baseline, and "Entry" deflates the bags almost to the bumpstops, lowering the air springs 2.5 inches. The system was originally designed several years ago by Delphi Chassis for Chrysler as an option for the '99 Grand Cherokee, but the project was scrapped two years ago. Our guess is even if the system doesn't make it on a full-size Ram, where the design seems ideally suited, the Grand Cherokee or the next-generation full-size Grand Cherokee will require this type of system to compete with the air-bag suspensions found on the Ford Expedition/Lincoln Navigator and Range Rovers.

We found the prototype Delphi suspension system on the T-Rex to be surprisingly responsive to ATV-sized dirt trail swells, allowing the front axle, and both rearends, to stay locked to the ground where previous leaf- and coil-spring experience had us waiting to go airborne. The system seems to react immediately to soften the compression side, while stiffening the bags on the rebound side to prevent the typical stiff-suspension full-size truck bounce. We found the system tuned to handle the lower-speed axle motions with ease, while higher speed, fast-frequency responses were more similar to stiffer-riding 3/4- and 1-ton suspensions when hauling close to a full load. That's quite an accomplishment for a truck that weighs 700 pounds more than a BR3500 standard-cab dually.

Dueling Transfer Cases
From the beginning, the idea was to create a 6x6 with tandem-driven axles; i.e., a traction monster. "We'd seen a lot of tandem-axle trucks where the third axle was dead, purely for load carry capacity," says Nick Rosenthal, the only full-time staff Project T-Rex engineer for the concept: "We wanted a way to drive both rear axles for maximum off-pavement capability." Many designs were entertained, mostly looking at heavy-duty military trucks and carriers from around the world. However, in keeping with their feet-planted-on-the-ground parameters, Nick and Leon eventually decided on off-the-shelf components. Knowing they needed something strong enough to manage the huge torque and horsepower numbers of the built V-10 (more on that to follow), a heavy-duty Hummer NVG 242 full-time transfer case (with 2.72:1 low-range) was selected and modified to allow for part-time duty as well, as in the Jeep Cherokee, Grand Cherokee and Dodge Durango four-wheel drive system. Various internal parts were heat-treated to increase their overall strength, while the chain drive itself was increased in width by two full chain links, also significantly adding to its capacity. The end result is called an NVG 244 HD. The 'case offers four separate four-wheel and six-wheel drive options, all controlled by a rotary dial on the dash, and includes a driveline-releasing Neutral position.

The second transfer case is mounted directly to the first rear Dana 60 with the input shaft shooting straight through to the pinion. Obviously, there's no reduction gearing in this case to make sure both axles turn at similar speeds.

The first transfer-case option is called "4WD Full-Time," in which only the rear output shaft of the 244 is turning (similar to conventional part-time two-wheel drive); however, T-Rex uses a dual transfer-case setup whereby the rear driveshaft out of the first transfer case is connected straight to the second 'case (a Dana unit with a 1:1 gear ratio) that's mounted onto the first rearend pinion yoke. The chain-drive output shaft of the Dana transfer case runs over the first Dana 60 rearend to a carrier bearing that sends power through a second driveshaft to the back Dana 60 rearend. Basically, when power is sent to the rear axles, on high-traction surfaces, all four wheels will turn. This gives new meaning to the conventional idea of "full-time four-wheel drive." Confused? Think of it as a regular two-wheel (i.e., rear-wheel) drive, only with four (rear) wheels turning.

Because of its size and weight, the Dana 'case needed a separate damper to minimize the vibrations and sharp motions a typical rearend made to work must endure. The 'case is rotated to allow the output shaft to pass over the axle tubes, where a carrier bearing (incorporated into the gussetting of the third member) mounts to a yoked driveshaft to drive the final offset-pumpkined Dana 60.

Next, the transfer case offers "6WD Full-Time," where the center differential and all axles are open, functioning in the standard high-range. In this case, power is sent to the front Dana 60 via the open center diff. Next in line is the "6WD Full-Time Locked" position, also in high-range, that mechanically locks both the center 244 differential and electro-magnetically locks the Dana transfer case-to be used only in low-traction situations. (There is a "Neutral" selector on the dial for emergency towing, along with a deactivation mode on the load-leveling air spring suspension.) And finally, the "6LO" position locks the 244 'case in low-range, locks the Dana 'case, and automatically locks up the three Torsen Dana 60 differentials for mega-maximum traction.

The control dials for the suspension and dual transfer-case combination are easily accessible via dash dials, mounted within easy reach just below the factory Infinity CD/radio controls. The one-of-a-kind NVG 244 transfer case allows for a full range of options; from both rear axles to be driven during normal, everyday operation (open diff "Full-Time 4WD"), to fully locked extreme-traction situations (all three axles and both 'cases electromagnetcially locked in "6-Lo''). And for those rare and exceptional situations, T-Rex does offer a "Neutral" position in the transfer case.

We liked the ease of operation of the twin dash dials to customize the suspension and transfer-case settings to any terrain or towing need. Being able to choose, and experiment with, the settings depending on the circumstances occurs to us to be a darn smart use of technology. At a time when many manufacturers are trying to make systems invisible, idiot- (as well as litigation-) proof, it's nice to see a design that puts a little faith in the abilities and skills of the driver-even if it is just a concept.

V-10 Power
In the beginning, the T-Rex project team used theoretical upgrade numbers of 400 horsepower and 500 lb.-ft. of torque as load parameters for the axles, transfer cases, and transmission. When the engine team came back with 100 more horsepower and lb.-ft. of torque than they were originally hoping to get, we're told more than a few jaws dropped to the floor.

The team slapped a stock 8.0-liter V-10 on the table, then started playing with it the way Walker Evans might if he were going to race in the next Baja or Daytona NASCAR Super Truck race. A new billet crank, 12:1 ported and polished heads, a new cam grind, bigger injectors, forged steel rods, and aluminum rollers are among the performance items. With better air flow on both the intake and exhaust, plus the added advantage of a newly remapped J-Tech Mopar computer, the biggest motor alive for a factory full-size pickup becomes even more impressive.

Naturally, something with this much compression would be impractical on city streets. We didn't get to drive the truck long enough to collect mileage numbers, but we could guess that government CAFE restrictions would be a serious obstacle.

As we were filling up on the 108-octane race fuel T-Rex likes to drink, it struck us that the new Cummins, due out next year, would be a better match for a tow vehicle of this size, quality, and stature. When we suggested a new six-speed transmission hooked up behind the new Cummins to two T-Rex engineers, they just looked at each other. . . with smiles on their faces.

All Smiles
As you can imagine, the engineers weren't the only ones with smiles on their faces. Driving a vehicle like T-Rex is like a birthday, Christmas, and the lottery all rolled into one big package: suspension controls, 6x6 Low-Range, custom eight-way adjustable seats, twin-tube shock adjustments, and a fierce V-10 when you put your foot into the throttle.

Dual actuator tanks give the system the ability to react to a wide variety of demands without overheating the compressor. The tanks are mounted between Dana 60 No. 2 and Dana 60 No. 3, well out of the way of any flying debris. Because of the necessary proximity of the two driven rear axles and the design of the driveline, the second driveshaft is quite short. As a result, the back Dana 60 had to be tilted slightly, with the third member offset to the passenger's side of the truck.

Whether or not this truck goes into production-as much as we'd like to see it or some deviation of it-is a moot point. We have no doubt there is at least some part, maybe many parts, that will eventually make it to the full-size Ram, or Dakota, or the next big Jeep-maybe even the next small Jeep. Given that so many of the pieces that make up T-Rex were pulled "off the shelf," we can see that as nothing else but a big, bold sign of encouragement that more good things are coming from Chrysler. T-Rex, unlike its extinct carnivore namesake, looks to have a healthy future relying on the strength of past and present technology.

SPECIFICATIONS
GENERAL
Vehicle/model Dodge T-Rex
concept regular cab
ENGINE
Type 90-deg. cast-iron V-10
Displacement (cu. in./liters) 488/8.0
Bore x Stroke (in.) 4.00 x 3.88
Compression ratio 12:1
Fuel Injection Sequential Multiport
Valve gear OHV; 2 val./cyl.
Redline (rpm) 5,400
Race Fuel requirement 108 Oct.
ENGINE OUTPUT
Mfg.'s ratings:
Hp @ rpm (SAE net) 497 @ 5,500
Torque (lb.-ft.) @ rpm 593 @ 3,700
ACCELERATION
Mfg.'s testing:
0-30mph (sec.) 3.3
0-60mph (sec.) 7.7
Standing 1/4-mile (sec. @ mph) 16.09 @ 88
DRIVETRAIN
Transmission 47-RE "Uprated"
Ratios: 1st 2.45:1
2nd 1.45:1
3rd 1.00:1
4th 0.69:1
Rev. 2.20:1
Axle ratio 4.10:1
Final drive ratio 2.83:1
Engine rpm @ 55 mph 1,850
Transfer case, front/rear Part-time & full-time
NVG 244 / Dana
Low-range ratio, front/rear 2.72:1 / 1.00:1
Front drive None
SUSPENSION/AXLES
Front axle 4 trailing arm,
track bar, progressive air bags/Dana 60
First rear axle 4 trailing arm,
track bar, progressive air bags/Dana 60
Second rear axle 4 trailing arm,
track bar, progressive air bags/Dana 60
STEERING
Type Power assist, recirculating ball
Turns, lock to lock 3.2
Overall ratio 14:1
Turning diameter, curb to curb (ft.) 43.33
BRAKES
Front 12.0x1.5 vented discs
Rears 13.0x3.5
Power assist Hydraulic tandem diaphragm
Swept area (sq. in.) 1,179.3
Rear Antilock 4W
BRAKING DISTANCE
60-0 (ft./sec.) 180 (est.)/4.73
WHEELS AND TIRES
Wheels Mickey Thompson
16x8 aluminum alloy
Tires 265/75R16 Michelin A/T LTX
DIMENSIONS AND CAPACITIES
Wheelbase (in.) 133.5
(measured at center of 2nd and 3rd axles)
Length (in.) 232.0
Width (in.) 79.4
Height (in.) 80.2
Track, f/r (in.) 69.8/69.2
Bed dimensions, LxWxH (in.) 103.5x64.2x19.4
Base curb weight (lb.) 6,840
Base weight distribution, f/r (%) 55/45
GVWR/GCWR (lb.) 12,000/26,000
Payload (lb.) 5,000
Max. towing capacity (lb.) 14,000
Fuel capacity (gal.) 26
ACCOMMODATIONS
Seating capacity (people) 3
Headroom (in.) 40.2
Legroom (in.) 41.0
CALCULATED DATA
Power-to-weight ratio (lb. per hp.) 13.76:1
Specific output (hp. per liter) 62.125:1
Brake swept area per ton (sq. in.) 344
Ramp Travel Index We can only guess

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