Caterpillar CT681 Designed for New Markets

Dec. 17, 2014

The first thing you see when you approach Caterpillar’s masculine CT681 heavy truck is the plain-Jane (plain-Zane?) front end, unless you sneak up from the rear. Even from there you’ll notice its other major feature: a set-forward steer axle shod with big wheels and tires. The axle’s center is just 28 inches behind the bumper, said to be the shortest BA dimension in the business.

Yes, this is a bridge-formula truck aimed at fleet operators of dumpers and mixers who’ll be the CT681’s main customers. Got snow this winter? Then watch for a CT681 with a big plow blade, because heavy snow-plow service with highway departments is a third target.

CT681 Specifications

  • Truck: Caterpillar CT681, conventional-cab 6x4 straight truck, BBC 114 in., BA 28 in., 12.25-in.-high frame rails w/ 120,000-lb. yield strength
  • Engine: Cat CT13, 12.4 liters (758 cu. in.), 430 hp at 1,700 rpm, 1,550 lb.-ft. at 1,000 rpm
  • Transmission: Caterpillar CX31, locking torque-converter 6-speed powershift, overdrive 5th and 6th
  • Front axle: 18,000-lb. Meritor FL-941 on 18,000-lb. parabolic leafs
  • Lift axle: 8,000-lb. Watson & Chalin SL-0890 steerable, air-sprung, w/ 17.5-in. wheels and tires
  • Tandem: 40,000-lb. Meritor MT-40-14X-4DCR w/ 4.63 ratio and driver-controlled Locking differentials, on 40,000-lb. Hendrickson HaulMaxx rubber-spring walking beam
  • Wheelbase: 246 in.
  • Tires, wheels: Continental 385/65R22.5 front, 11R22.5 rear, on Alcoa Durabright polished aluminum discs   
  • Fuel capacity: 100 gallons
  • Body: 17.5-ft., 21-cu-yd. Bibeau BFL-S, AR450/AR550 steel dump

All those potential owners prefer simple looks, and that’s why the “industrial” styling, Cat executives said in presenting the truck recently. And they emphasized that, like the earlier CT660, it’s a real vocational truck with options like “true” front frame extensions, not bolt-ons, to carry pumps and other gear for various types of service. The company launched its Cat Truck program with the axle-back 660 three years ago.

That begs the question, why did it take so long to come up with the axle-forward version? Execs say it’s because they’re going slow with the program, giving themselves and Cat dealers time to learn, sell and service the product. They readily acknowledge that Cat Trucks are based on the International PayStar and assembled by Navistar, and their CT13 diesels are Navistar N13s that are painted yellow. But they emphasize that Cat engineers and product planners are responsible for much of the design work and enhanced features that put the CT Series several cuts above the PayStar. And they say they monitor assembly at Navistar’s plant in Escobedo, Mexico.

Climb in a CT681 and you feel extra quality as well comfort and quietness, and you know you have the ability to do more than a full day’s work. The cab feels tight partly because of personal experience of Dave Schmitz, product manager in Cat’s Global Truck Sales division who was also in on the CT660’s design. “My father and uncle were in the ready mix business in Milwaukee,” he said. “I remember it was always dusty – dust all over the place—and noisy. So we took that into account in designing our cab” with an air filtration system and noise-reduction insulation.

The dumper I drove—basically a 10-wheeler with a single, small-wheeled lift axle ahead of the tandem—ran strongly on a gravelly off-road course at Cat’s demonstration center west of corporate headquarters in Peoria, Ill., and on nearby highways. Its Bibeau steel dump box carried 15 tons of sand, said Brad Zingre, a Cat industrial sales representative who was along to answer questions. Add the truck’s tare weight of about 26,000 pounds and we were at 56,000 pounds gross, so the pusher axle stayed in the air. On the course and out on the road, I paid special attention to maneuverability and powertrain performance.

A forward-set steer axle limits wheel cut left or right, especially with wide wheels and tires, so a driver has to immediately begin spinning the steering wheel in the desired direction while starting a 90-degree turn—something I had to quickly relearn on my first turn. “Rookies get one back up,” if you know what I mean. But limited turnability also requires more room on tight job sites, something regular drivers know and take in stride.

Helping in such fore-and-aft maneuvers in this truck was an automatic transmission, specifically Cat’s own CX31. It’s not a cheap option, but half the buyers of CT660s have been taking it, our hosts said. (Cat also offers Eaton manual and UltraShift automated gearboxes, but no Allison automatics.) CX means on-highway and 31 is the diameter of its internal clutches in centimeters, by the way. It’s based on a powershift transmission first used in 2005 in a Cat off-road articulated dump truck; it has six forward ratios that move a truck from a dead stop to 65 mph or more on the highway. With a 4.63 ratio in our truck’s rear differentials, 70 mph was about it.

The CX in this dumper was unfailingly smooth and positive in its shifting. Earlier CX31s I drove would occasionally thump during an up- or downshift, but not this one. After making a couple of 30- to 40-mph circuits amid clouds of dust on the test course, I repeatedly stopped and started the truck on upgrades to see if I could make the torque converter slip or the drivetrain shudder. Several times I let the truck roll downgrade, forward while in Reverse and backward while in Drive, then hit the gas, and it quickly stopped and easily started upward. I was impressed.

The 12.4-liter CT13/N13 has five ratings, from 365 to 430 horsepower and 1,250 to 1,550 lb-ft, all governed at 2,100 rpm. This displacement and these outputs are sufficient for most vocational jobs and customers are satisfied with the engine, Cat personnel say. Since Navistar dropped its MaxxForce 15 program, which was supposed to include the block and crankshaft from the old Cat C15, there’s been nothing bigger available. Cat says there’ll soon be an announcement on a 15-liter engine, so we’ll see. Anyway, the 430-horse CT13 in this truck was very responsive and worked well with the autotranny in propelling us on road and trail.

With an 18,000-pound forward-set axle drivers can anticipate a stiff ride, and it was. There’s not enough room for long leaf springs, even if they’re parabolic in design, so the nose and cab hopped over bumps and bowed concrete out on the highway. I was fine in my air-suspended seat, but Zingre’s perch was on steel legs and he had to hang on at times. Of course, trucks like this seldom go out with a passenger, but if I were a Caterpillar dealer and this were my demonstration truck, I would install an air-ride seat over there to keep a potential customer in a buying mood.  

Maybe you’re wondering why the new Cat Truck is labeled 681. What happened to 680? It’s coming sometime next year and will also have a forward-set axle, but it’ll be a long-nose tractor, our hosts said. That’s a more premium market, so the CT680 will have more bright-metal trim available. Watch for it.