Concrete is poured where it needs to be, but people who produce and haul it say it’s “placed.” What’s the best way to do that? Many in the business believe it’s with a front-discharge mixer truck, which rolls right up where the concrete is needed. Its driver sits in the cab and operates the drum and the forward-facing chute, moving it exactly to where the crew wants the concrete put down and at just the right rate. Depending on the job, the contractor can eliminate one worker from his crew, so they often request this type of truck for deliveries.
Front-discharge, rear-engine mixers are rare to nonexistent in some areas, such as southern California, where rear-discharge mixers on conventional chassis are the rule. These cost less to buy, though folks who sell the front-discharge type argue that they are less pricey in the long run because they work fast and can sometimes make more runs in a day, and they can be rebuilt to achieve longer service lives. Glider-kitting these is common where it’s almost never done with a conventional. Front-discharge mixers are popular in the Midwest, where they’re made, though they originated in Salt Lake City.
Oshkosh S Series Test Set
Truck: Oshkosh S Series front-discharge, rear-engine, center-cab mixer chassis, tare 33,950 lb., GVW 80,000 pounds
Engine: Cummins Westport ISX12 G, 11.9 liters (726.2 cu. in.), 400 hp @ 1,800 rpm; 1,450 lb.-ft. @ 1,200 rpm
Transmission: Allison 4500 RDS full automatic, 6-speed double-overdrive
Front axle: 23,000-lb. Oshkosh 23K on taperleafs, w/ Sheppard XD 120 integrated hydraulic power
Transfer case: Oshkosh 21000 2-speed
Lift axle: 25,000-lb. Watson & Chalin AL-2200 nonsteering
Tandem axles: 46,000-lb. Meritor RT-46-160 w/ 5.63 ratio, on Hendrickson Primaax air-ride
Wheelbase: 196 inches
Tires & wheels: 445/65R22.5 Goodyear G278 MSD, on 22.5x13-in. Alcoa aluminum discs
Brakes: 16.5x7-in. S-cam at all wheels
Fuel tanks: Two 37.5-diesel-gallon-equivalent, Type 4 (polymer core w/ carbon fiber wrap)
Body: 11-cu.-yd. McNeilus forward-facing drum, w/ ZF P7300 transmission and Eaton hydraulics
Since its advent in the mid-1980s, Oshkosh’s S Series mixer has become one of the principal products of this type, and the company produces new and refurbished chassis in a plant in its namesake city in Wisconsin. I drove this new one on a recent visit to Oshkosh’s service center, and also got some quick instruction on how to manipulate the chute and run the drum from Greg Steffens, an Oshkosh project engineer.
He and Mark Broker, a senior design engineer, noted that this truck had a Cummins Westport natural gas engine: the 11.9-liter ISX12 G. Gas is not new for Oshkosh and its McNeilus subsidiary, which between them have built more than 8,000 such trucks since 2008, they said. Many of that number are trash-packer trucks that are a large part of McNeilus’ business, in Dodge Center, Minn.
This four-axle mixer chassis was the first assembled with two large vertical gas tanks mounted to the left- and right-front of the rear engine compartment. Oshkosh showed the truck at Conexpo in March. The tanks replace four smaller steel tanks stacked horizontally ahead of the hood. The new configuration with the two lightweight composite tanks saves about 500 pounds and allows easy access to the engine.
Climbing up and into the S’s low-slung, center-mounted cab takes some thought and practice for somebody who doesn’t do it every day. Once inside, the steering wheel, foot pedals and gauges are familiar looking, but not much else is. Controls immediately to the right run the drum and chute, but they’re also different from what’s in a conventional mixer truck’s cab. Steffens knelt on the fender to my left and showed me how to use them. A lever activates cylinders that unfold the three-piece chute, which is long enough for close-in pours; the driver has to get out to hang extensions if the chute needs to reach farther, and of course to clean out the chute and stow the extras afterwards.
A joystick moves the chute left or right and up or down. Push buttons on the stick speed or slow the drum to regulate the pour rate. When it’s done and everything’s washed, the chute is folded up and parked at an angle to the right. It mustn’t be parked too far over, or it would extend beyond legal width limits and could collide with trees, poles and other things that line a street. So a rubber bungee cord hangs down from the top of the chute as a marker, Steffens said. When the right side of the chute touches it, the truck doesn’t exceed 8 feet wide—low-tech but clever.
I wished there was some concrete in the drum so I could practice pouring—placing—it, but no. However, the truck was very drivable, so off I went. From outside, the S’s one-man cab might look narrow, but it’s plenty roomy (and a two-man training cab is an option). It’s also rather comfortable, with a supportive bucket seat and good leg and elbow room. It has just a few gauges that tell the driver all he needs to know, and modern suspended pedals.
There are only two pedals because an Allison automatic transmission is standard in the S, as it is in all front-discharge mixers. Originally they were built with manual transmissions, but long shift linkage from the cab to the tranny ahead of the engine could be troublesome. Also, the truck must move fore and aft to precisely place the concrete, and operating a shift lever and clutch along with the chute and drum is more than a handful. With an Allison, the driver punches D or R and feathers the accelerator and brake as required as he moves the chute. When the pour’s done and the cleanup’s completed, it’s back for another load. For on-pavement travel, D is all that’s usually needed.
With the gas engine out back, the quietness is almost eerie. I couldn’t hear it idle, and its working growl faded away as road speed increased. Cummins Westport G engines are quiet because they are spark-ignited; a diesel’s compression ignition is more efficient, but that produces the diesel’s pounding sound. At highway speeds, the chassis produced some muted mechanical whirring and tire whine, and the slight sound of air rushing past the mirrors and the cab’s front corners. Ride was smooth, even with a stiff front suspension and the blocky Goodyear 445-series tires.
Acceleration was almost brisk as I departed and headed for nearby Wisconsin Highway 26 and turned south. I cruised at 55 to 65 mph, where the 5.63 axle ratio had the engine spinning at 1,600 to 1,800 rpm—not wound out, but far faster than today’s low-revving diesels in road tractors. This was the highest-rated ISX12 G, and it made plenty of power. If it was consuming fuel at a fair rate, so what? Natural gas is much cheaper than diesel, so savings will help pay off the gas system’s premium, which is in the tens of thousands of dollars. However, some of that is often offset by government grants.
I turned right on a county road and followed it west and north a ways. I stopped and backed into a deserted intersection to reverse course and return the way I came. Maneuvering was easy and the view out the cab’s windows and through its mirrors was fine. I meandered along other roads and onto city streets, and at one point did a couple of circles on a gravel parking lot. The wide tires limit wheel cut and make the turning circle a bit big, but it seemed to corner better than a conventional with a forward-set steer axle and wide tires. With Sheppard power steering, the truck didn’t require much effort to turn, even while crawling. That’s part of what makes this a seriously productive truck.