Test Drive: Mack's Granite MHD

One way to cut weight and cost from a new truck is to choose a relatively small engine.

This is the essence of the Mack Granite MHD, announced early this year and recently put into production.

Meant for medium- to heavy-duty work, the MHD uses an 8.9-liter Cummins ISL9, which shaves several hundred pounds and several thousand dollars off the price of a regular Granite with a large-bore Mack Power diesel. The MHD is aimed primarily at municipal fleets and private operators that don't need a full-fledged Class 8 truck but still have some heavy chores to do.

It comes as a 10-wheeler, with tandem rears but no lift axles, and only as a straight truck. A single-rear-axle version might expand its appeal to municipalities, but Mack has no plans at the moment to take it in that direction. For one thing, an otherwise premium Granite might be too pricey against medium-duty trucks that compete for such business.

Except for the medium-displacement, heavy-duty engine and accompanying transmission, the MHD is a true Granite, with a solid steel cab, hefty frame rails and everything else found on heavier versions. It felt and drove like a Class 8 truck but with somewhat less oomph, a situation soothed by the constant power flow through its Allison automatic transmission. This made it a very easy truck to drive, and is also typical of how city and county fleets buy their trucks. Municipal-ities were early Allison adopters.

I did my driving out of Allentown, Pa., Mack's former headquarters and still the place where fleet managers come to see and inspect their new trucks, which are assembled in nearby Macungie. This is done at the Mack Customer Center, housed in the former technical center complex. There I met with Curtis Dorwart, vocational segment manager. He explained the MHD's features and accompanied me as we drove a new MHD to a quarry outside of Easton.

At the quarry I met Bob Evans, a retired Mack engineer who now works as a photographer. He guided me along the trails that meander through the complex, and we both watched out for working trucks, which were constantly coming and going. Evans had found a place between two tall piles of crushed stone to pose the truck, and I snapped some shots there while he moved the MHD up and down the trail.

Quiet ride

Otherwise Dorwart and I stayed on area streets and highways, some smooth and some rough, as one would expect in a cold climate. The temps on this mid-August day were in the 70s and skies were sunny - an unexpectedly beautiful day at a time when high heat and humidity are normal. We ran the powerful air conditioner at first, but I soon shut it off and we rolled down the windows to enjoy the comfortable outside air. We rolled them back up while at highway speeds, and the cab's interior then was very quiet.

Folks at the A.B.E. Materials quarry had put 11.69 tons of #10 stone in the dump bed to give the truck some working weight and move the gross vehicle weight to 58,400 pounds, according to the scale ticket Dorwart handed me. Technically this was 3,800 pounds over its rated GVW, based on axle capacities. The load settled down the AL461 rear air suspension, and my suspension seat took care of any harshness that got into the cab. The passenger seat was on solid mounts, but Dorwart didn't bounce around much.

The ISL9 diesel and its natural gas-fueled brother, the ISL-G, are the only Cummins engines now used by Mack. It dropped the Cummins ISX a while ago when it quit making the CL long conventional, and for a time returned to its roots where only Mack engines powered the bulldog-adorned trucks. It could conceivably have sourced a midrange diesel from Volvo of Sweden, its corporate parent, but that would've required certifying a new engine with the U.S. EPA, which is not a cheap proposition.

Using the ISL9 was more expeditious and a better bet as something to sell here in the U.S. Cummins is a familiar name, and the medium-size, heavy-duty engine is increasingly popular because other truck builders also employ it in various models similar in mission to the Granite MHD. Mack uses the ISL-G in its TerraPro MR heavy low-cabover that works primarily in the trash business.

Easy driving

Smaller displacement of course limits horsepower and torque. This engine's rating was 345 horsepower and 1,150 pounds-feet. This was fine on level streets. All I had to do was stomp on the accelerator, and the 6-speed Allison with its locking and unlocking torque converter made the most of whatever was at the flywheel. With our moderate load there was no problem keeping up with traffic. Motorists following us on a narrow, winding highway on the outskirts of Easton probably wished I had moved faster, but the truck's bulk and slightly top-heavy feel kept me cautious.

On steep grades the ISL pulled gamely, though our road speed dropped to as low as 45 mph on one long hill along old Pennsylvania 309. If the engine had been bolted to a manual tranny of some kind (an Eaton 10-speed is standard), I'd have been rowing through the gears a bit. And it'd have been far more work to drive in town.

The Allison takes away so much work, and cuts driver training and cushions the driveline so nicely, that I sometimes wonder why everybody doesn't get one. Then I saw the price Mack set for this Allison.

The 3000 RDS autotranny in this truck lists at $15,000 over the manual, Dorwart said. That'll buy a lot of clutches and U-joints, and there are still a lot of guys out there who can handle a manual, so the privately funded fleet will usually stay with a crashbox. Municipal fleets, though, do more than haul gravel, and the Allison is true salvation when a bleary-eyed guy is on his 12th straight hour of plowing snow and it's still coming down.

With a large-bore engine, the Allison would need to be a 4000 series, which costs even more. That's another good reason to use an engine like the ISL9 or maybe the ISC8.3 in a truck like this. But the beefier "L" is a wiser choice for the Granite MHD with its high-capacity tandem rears.

Otherwise this Granite looks and is equipped like any other Granite, and that's a good thing, because it's roomy, comfortable and rugged. It replaced Mack's venerable RD and other vocational trucks that were rugged but definitely not cushy. The MHD's interior has plenty of room for driver and passenger. Dump-body controls are between the seats. The two-panel dash holds gauges, switches, parking brake valve, info display panel and Allison selector keypad.

Sometimes I wonder how guys withstood driving the older models. Then I remember an outing in Boston about 10 years ago, while the infamously expensive Big Dig was a-diggin', when I drove a CL and an RD. I actually came away preferring the RD, because it was more compact and easier to see out of. You see, Mack had improved the RD over the years - but the Granite is far, far better.

So, get a Granite in MHD trim with the ISL9, or with any of the bigger MP diesels, and get to work, if you can. We all hope government policy and economic conditions will soon make it happen, but that's another story.

From the October 2011 issue of HDT.