Mack Granite Axle Back
This one's made for heavy loads and tight turns in many eastern and central states.
Tom Berg
Senior Equipment Editor
Mack Trucks has produced vocational variants of its venerable R model for about four decades, and they have worked so long and well that customers continued to buy them until better Bulldogs trotted on the scene.
Those arrived in 2003 as Mack's Granite series, first unveiled with forward-set steer axles usable where weight laws favor wide-spread axle settings. The latest is the Granite Axle Back, made for many eastern and central states where axle weight rather than axle placement is important.
The AB's steer axle is 50.5 inches behind the bumper, or 20.5 inches more than other Granites. It's what gives the new Axle Back model its name and its function. Also standard on the new truck is a higher-capacity Cornerstone frame with taller main rails than those used on the Granite and Granite Bridge Formula models introduced earlier.
The Granite Axle Back can take high upfront loads by virtue of beefy axles and taper or multileaf suspensions rated at up to 23,000 pounds. It claims exceptional maneuverability because of wheel cuts made as tight as wide wheels and tires allow.
Those characteristics resulted in a firm ride and exceptional maneuverability in the mixer chassis I drove during the AB's introduction a couple of months ago at the Las Vegas Speedway in Nevada.
With its Beck Industrial mixer drum carrying about eight tons of gravel, the truck scaled at 47,800 pounds - better than 10 tons under its rated gross weight - so the 10-wheeler's front end bounced a bit on its stiff springs. And with plenty of room on the parking lot, I could easily execute some short-radius circles to simulate turn-arounds at job sites.
Drivers among the press corps were limited to coned-in courses on the lot. So there wasn't enough room in the designated straightaways to get the mixer past about 45 mph in top gear. As a result, I couldn't get a feel for the claimed 365 horsepower that the 12-liter AMI-335 claims to make at 1,700 to 1,900 rpm. The Maxidyne's simple internal exhaust-gas recirculation is unique among American-made diesels, but to breathe properly it needs higher revs than previous Maxidynes.
The AMI Maxidyne has a narrower operating range, so it needs at least one extra gear than the five-speed used so often in Maxidynes going back to the 1960s. In this truck there were more than enough ratios available with the 11-speed Eaton Fuller "LL," basically a nine-speed with a low-low range for starting on upgrades with heavy loads or creeping around job sites. If you use all forward gears, they add up to 11; this tranny shifted easily and had a nice, solid feel to the lever.
This vehicle was obviously built for a patriotic customer (check the starred-and-striped drum) in Texas. The Lone Star State's weight law allows as much as 46,000 pounds on the tandem and 23,000 on the steer axle, which allows a mixer to carry 10.5 yards of concrete on the three axles, according to Clint Campbell, sales manager at Dallas Mack Truck Sales and the guy who sold this truck. Those generous limits apply only to mixer and trash trucks.
Somehow this chassis wound up with a 20,000-pound Mack front axle. Others ordered for the customer - American Concrete in Weatherford - get 23,000-pound fronts, Campbell says. The tandem is a 46,000-pound Meritor with 4.89 gears on a Chalmers suspension. The suspension and axles clunked a lot as we climbed over a row of dirt moguls on an artificial off-road course - not surprising, given the long stretching required to allow the tandem axles' ends to articulate.
The Granite's steel cab is based on the CH's, but is stoutly reinforced to take the stresses found while running off-road. It's the strongest cab Mack's ever built, according to Steve Ginter, the vocational segment product manager who answered my questions during this drive. The instrument panel and interior trim are similar to a CH's, too, with a pleasant but no-nonsense ambience that makes a guy want to work - or at least you hope so if you're the boss.
The Axle Back's bumper-to-back-of-cab measurement is 112 inches, compared to 108 inches on the other Granites. Those numbers assume a bumper that's almost flush against the nose, as on this truck. Sometimes the bumper's set well forward of the nose to accommodate a front-drive PTO, a snowplow mount or transmission cooler. To clear any such stuff, the Granite's grille remains vertical as its fiberglass hood tilts.
See those big, grey fender flares? They're made of a plastic that flexes without damage if one hits something - a pretty neat idea. And I would have put the headlamp/turn signal fixtures more inboard where they'd be protected from sideswipes.
The Granite Axle Back has replaced Mack's old RB, a vocational model which just went out of production, and will replace the offset-cab DM when it's phased out late this year. Those models have been around for about 40 years.
And while Mack says the Granites are likely to see replacements sooner, you can bet on them being as long-lasting as their predecessors.
