All about front discharge mixers

Time is money, and that’s the essence of a front-discharge mixer. It drives right up to where concrete’s needed and, after the driver adds chute extensions, starts offloading.

This six-axle FDB6000 for Ohio has three air-suspended lift axles, including a hydraulically operated rear booster that stays down even when the barrel’s empty to reduce chassis bounce.
The driver controls the chute, hydraulically pointing it exactly where it’s needed and at a flow rate the crew can handle. In fact, the “chute man” can be eliminated from the crew, saving the contractor money. 

For ready mix fleets, the fast operation sometimes enables a truck to do one extra load a day, which adds to revenue and profit. But rear-discharge mixers cost less to buy and, some say, to maintain.

Terex/Advance Mixer in Fort Wayne, Ind., makes rear-discharge drums for mounting on conventional truck chassis, but its heart is in the front-discharge version that it builds all-new and as glider kits.

Like other mixer makers, Terex went through a wrenching time during the Great Recession. Parts and service people stayed busy as concrete producers kept their old trucks running. But the truck business about died, related Dave Rinas, the director of sales and marketing, during HDT’s visit earlier this year. So Terex shut down its factory for a year. Managers took advantage of the downtime to rearrange the plant for greater efficiency and to redesign their FD series of mixers. The multi-axle truck you see here is one result.

Noticeable changes

The new FD models look similar to previous trucks. But more cab interior room and a shorter turning circle add comfort and quickness, and electrical changes make the truck easier to maintain.

A 2013-model MTU 1300 engine includes electronic on-board diagnostics, a new Environmental Protection Agency requirement. Because it’s otherwise an EPA 2010-spec engine, it has a DPF (left) and urea dosing chamber as part of its vertical exhaust stack.
A 2013-model MTU 1300 engine includes electronic 
on-board diagnostics, a new Environmental Protection 
Agency requirement.  Because it’s otherwise an 
EPA 2010-spec engine, it has a DPF (left) and urea 
dosing chamber as part of its vertical exhaust stack.

Terex began producing the new trucks last October. In the pre-delivery shop, Rinas and others briefed me on the changes, using the test vehicle as a massive prop.

It was an FDB6000, meaning Forward-Discharge with a long-armed rear Booster axle, with six axles total. Like all new Terex trucks, this one had a set-forward front-driving axle mounted to slightly shorter leaf springs, plus repositioned steering gear. These alterations were made to cut weight and provide more cab room for drivers. They also allow the wide front wheels to cut more sharply and reduce the turning circle by 10% to 25%. This was noticeable when I drove the truck.

Also obvious were the 8.5 inches of extra legroom (I could really kick my short legs out, and long-legged guys should be comfortable, too) and several inches more overhead room in the enlarged, stainless steel cab.

The legroom came partly from stretching the wedge-shaped nose by 3 inches, which also made space to house air and electrical junctions accessed through a removable panel. Rerouting air and electrical lines throughout the chassis should improve access to them, Rinas said. Also, the wiring harness is now modular and can be replaced in sections.

The old FD series had 13 basic axle and frame configurations, but to cut costs, the new model has just six configurations. These will cover 98% of the market.

Our subject truck was one of a healthy order from Ernst Enterprises, based in Dayton and with operations in Ohio, Indiana, Kentucky and Georgia. The truck had worked briefly in Ohio before returning to the plant for some adjustments.

Jim Aslin, a veteran truck specialist who covers the Northeast for Terex, explained that this truck’s rear booster, two pusher-type lift axles and long, 204-inch wheelbase are needed to comply with Ohio’s bridge-formula law. With an “outer bridge” (the distance between axles one and six) of 33 feet, 7 inches, the truck can legally gross about 75,000 pounds in Ohio. With a payload capacity of 47,000 pounds, it can carry 9 to 10 cubic yards of concrete. 

Taking it for a drive

I punched the Allison into Drive and moved out, making my way to nearby streets. I noticed that the heater blower was noisy, even at low speed, but that turned out to be my only gripe.

The FDB had far fewer gauges than most highway trucks, but included a toggle switch to engage the front-driving axle, plus a few more switches for the
locking rear differentials and the transfer case’s high and low ranges. I left those alone because I stayed on pavement and hard dirt.

Climbing down and back up with my camera to shoot photos was easy, thanks to well-placed steps and handles.

I had gotten a feel for the truck’s solid steering, strong braking and rather smooth ride by the time I drove down a ramp to Interstate 69 and some high-speed travel. There and on city streets, straight-ahead steering was agreeably stable with no wandering. Tight turns required quickly spinning the small, sporty wheel and then spinning it back to center.

With the tight wheel cut, I could easily make hard right turns from curb lane to curb lane, while watching that the rear end’s swing-out didn’t clobber anything.

Brakes were powerful. The pedal is now hung from above rather than hinged on the floor – another change in the new model.

With no load in the barrel there was some bouncing, but it was muted by my suspension seat, the long leaf springs on the steer axle and the air bags on the rear axles. There was a bit of vibration during hard acceleration, but that’s more than understandable with the power running through a transfer case and the three tandem gearboxes in a driveline and chassis set up to handle rough off-road travel.

The booster axle rode on air springs. Hydraulic cylinders pressed those two wheels against the pavement and took some of the load. Even with an empty barrel the booster stayed on the pavement to reduce frame springing and smooth the ride. It automatically lifted when I punched the Reverse button, then went back down when I re-engaged Drive. Meanwhile, as long as the engine was running, the barrel turned slowly to avoid flat-spotting its support rollers.

At 65 mph the 12.8-liter diesel revved at about 1,725 rpm, busy but within specs for a vocational engine. Noise was muted because of the engine’s far-away placement at the rear of the chassis. It was rated at 450 horsepower with maximum torque of 1,550 pounds-feet, so with no load in the barrel it accelerated well and got up to road speed quickly. I imagine this engine can propel a loaded truck quite well, too.

More on the engine

Regarding the engine brand: A competitive marketing situation requires Terex to call it the engine an MTU 1300, though it’s a Detroit DD13 in other companies’ product lines. MTU means Motoren und Turbinen Union, an old-line German company that entered a partnership with Detroit Diesel in the 1990s. That entity is now called Tognum North America, which sells Detroit engines under the MTU name in certain markets. At Terex, MTU has taken the place of Caterpillar, which left the on-road truck-engine business at the end of 2009. All of Terex’s initial new-truck production of the FD series was with MTU 1300s, but the Cummins ISX12 is now an option.

As a 2013 model, the MTU 1300 included on-board diagnostic equipment newly mandated by the Environmental Protection Agency. Otherwise it had EPA 2010 emissions equipment, with a diesel particulate filter and a dosing chamber for diesel exhaust fluid, the active part of selective catalytic reduction. These are mounted in a strongly braced vertical stack just to the left and ahead of the engine.

A new engine with its aftertreatment equipment costs about $45,000, which pushes up a truck’s price to over $200,000, Rinas said.

“Customers comment on the cost until they get the trucks. Then they like the fuel economy, which is substantially better [than pre-2010 diesels].”

Front-discharge vs. rear-discharge

Front-discharge mixer trucks have traditionally cost more than rear-discharge mixers on conventional chassis, Rinas acknowledged. “But in an apples-to-apples comparison, the difference is 15% to 18%.”

The “apples” include an Allison automatic transmission, standard with Terex but not on the other truck type. And an FD’s life-cycle cost is less, he said, because it lasts several years longer and can be glider-kitted to extend its life even more. Glider kits are 40% of Terex’s production and it’s common at competitors, but kitting is seldom if ever done with conventional mixer trucks.

So there’s the case for the front-discharge mixer in general, and the Terex/Advance FD series in particular. I’ve driven them before and always found them surprisingly quick and even fun to run. This latest model improves on that, and represents time well spent during the plant shutdown.


Truck: Terex Advance FDB6000, six-axle front-discharge mixer chassis, forward cab, rear-engine, six axles, w/full frame inserts, tare weight 36,300 lbs., GVWR 84,000 lbs., legal GVW 75,000 lbs.

Engine: 12.8-liter MTU 1300 (Detroit DD13), 450 hp @ 1,800 rpm/1,550 lb-ft. @ 1,100 rpm, w/engine brake and block heater

smission: Allison HD4560 fully automatic 6-speed double overdrive

Front driving axle: 22,000-lb. Marmon-Herrington MT 22H w/ hub reduction gears & 5.38 ratio, w/ 445/65R22.5 tires on aluminum discs, on steel leaf springs

Rear tandem: 46,000-lb. Dana Spicer 46-160 w/ driver-controlled differential locks & 5.38 ratio, on Hendrickson Primaxx air-ride, w/ 445/65R22.5 tires on aluminum discs

Brakes: 16.5 x 7-in. S-cam drums on front and rear drive axles, 15 x 4-in. S-cam drums on lift axles

Wheelbase: 204 inches

Pusher axles: 11,020-lb. Hendrickson Composilite air-liftable w/285/70R19.5 tires on aluminum discs

Rear booster tag axle: 13,200-lb. Watson & Chalin air-ride, hydraulic Hi-Lift T2 w/11R22.5 tires on aluminum discs

Fuel tank: single 75-gal. aluminum

Body: 11-cu. yd. Terex/Advance Mixer Package

Customer Service Favors Front-Discharge Trucks

Ernst Concrete uses front-discharge mixers because of its focus on customer service, says Vice President of operations Mark Vandegrift. Ernst, headquartered in Dayton, Ohio, has about 250 of the specialized trucks that run in Ohio, Indiana, Kentucky and Georgia.

Vandegrift says Ernsts was one of the first companies to use front-discharge mixers in the 1970s, not long after the rear-engine trucks began being built in Fort Wayne by the predecessor to today’s Terex/Advance Inc. Ernst runs that brand as well as some from Kimble and Oshkosh. It aims to keep a truck for 60 months then sell it, although in the recent downturn some trucks are running longer than that.

“It caters to the everyday residential customer,” Vandergrift says of the front-discharge truck. “They eliminate a man to run a chute. It’s a tremendous advantage for the customer, and now with the technology of the electronic joystick, with a good crew, you can unload more quickly than with a rear-discharge.” 

However, much depends on the individual construction job. Rear-discharge trucks are better for high-volume pours, such as building and roadway construction in big cities, and delivering thick, “low-slump” concrete.

Front-discharge mixer trucks are safer because drivers can better feel what the chassis is doing on job sites and in turns on paved streets, he says.

“Historically, we ran both, and historically, if we had a rollover, it was a rear-discharge,” he recalls. Rear booster axles have changed that somewhat because they add some stability, though they are primarily used to extend the wheelbase and add legal gross weight.

Good, skilled drivers are very important, and Ernst puts a lot of effort into finding them. The company recruits from local labor pools and puts applicants through aptitude and personality testing so it can find “the kind of guy you’d want representing your company,” Vandegrift says. The stringent screening means the company hires only 5% to 10% of applicants. Some are former over-the-road drivers, who Ernst also uses in its bulk cement and aggregates hauling.

Ernst buys all-new trucks instead of gliders.

“We have more upfront cost with new, but on the back end we have more resale, too,” he explains. “We’re putting in all the Tier IV engines,” which roughly correspond to the Environmental Protection Agency’s 2010 on-highway standards for diesel emissions.

“We’re just trying to be more environmentally friendly and stay in tune with the EPA. With gliders, you’re just putting the old engines back in the environment. There are a lot of unknowns with the new engines, but it’s what the future will be.”

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