The Slingos have had Mack trucks working in their operation in one form or another for more than 50 years and have recently taken delivery of a new 685hp Super-Liner coupled to an mDRIVE transmission with the new HD option.

Dean Slingo is the managing director of Slingo Earthmoving, a family business he and his father Graeme formed in 2006. The company is based at Castlemaine in the centre of the goldfields region of Victoria, where requests for their services are always in high demand.

The father and son team spent many years working alongside each other in the civil construction company Graeme and his wife Helen had been partners in for more than four decades. But a little over a decade ago Dean and his father decided to diversify, forming Slingo Earthmoving, and the two co-directors have been doing long days ever since, with little sign of slowing down.

“Dad‘s 72 now and we can‘t get him to slow down,” Dean said. “Everyone keeps asking ‘when is he going to retire?‘ but he enjoys working and retirement doesn‘t seem to interest him at the moment!

“We‘ve had Mack trucks ever since I can remember,” Dean recalled. “Recently I‘ve been getting requests to go further afield. With the longer distances the smaller day cabs aren‘t really practical, so the Super-Liner has expanded our area of operations significantly.

“Its prime role in our operation is to haul our low loader, transporting our machinery to the various job sites. That‘s why I specced it up with the 685 horsepower MP10 and the mDRIVE with the HD shift option. When you throw a 35 tonne excavator on the low loader it needs plenty of power to climb the hills around here.”

The MP10 under the hood is an inline six displacing 16.1 litres and producing 515kW (685hp) and 3150Nm (2300lb/ft) of torque. It uses a selective catalytic reduction (SCR) emissions control system, and because of its prodigious torque output, the 685 rating is only available with Mack‘s mDRIVE 12-speed automated manual transmission.

The Super-Liner‘s radiator with a frontal area of more than 1750 square inches is ideal for the high cooling requirements of heavy haulage and road train operations. The electronically actuated Behr viscous fan clutch aids in the cooling process and works according to actual need, delivering anywhere from 5% to 95% of fan engagement. Put simply, rather than being either fully on or fully off, the fan responds with incremental engagement dependent on the amount of cooling assistance required.

The MP10 685 produces peak power from 1550 to 1800 rpm and maximum torque  from 1000 to 1550 rpm. The mDRIVE transmission is programmed to let the engine  pull down deep into the rev range before downshifting, while at the other end of the  cale, upshifting surprisingly early to maximise the engine‘s phenomenal pulling  power.

The PowerLeash engine retarder produces up to 570hp (425kW) of engine braking effect at 2200 rpm. Manually shifting down a gear or two to keep revs up, it‘s capable of delivering effective retardation even at weights beyond 70 tonnes. The big Mack sports a King Bars Warrego bullbar that weighs about a quarter of the bars that have been on the fleet in years gone by.

“Some of those early R-models had great heavy steel bullbars that weighed close to a ton. To date it‘s collected a kangaroo two or three times a week and there is not a
mark on it.”

The Super-Liner has plenty of chrome and stainless in order to match the highly polished bullbar, and the company name appears in a stainless steel plate on the back of the sleeper, framed by a couple of bulldogs. All this is the brainchild of long-time dealer Darren Aitken from CMV Trucks in Laverton. Handpainted line and scroll work  was the work of Phil Duus, and completes what is a truly magnificent machine.

mDRIVE HD (Heavy Duty)

Mack engineers had spent several years developing and testing a toughened version of the mDRIVE before releasing the HD option for on/off-road duty. At the launch they explained that the HD option has tougher gears and synchronisers than the on-highway mDRIVE released in 2010, a gearbox which more than half of all customers for road-going Macks now choose. The HD also has a more effective oil cooler and uses higher-viscosity synthetic lube oil.

Weight and price are usually important key factors in the heavy trucks purchase decision process and the mDRIVE is among the lightest transmissions on the market. A single countershaft mDRIVE weighs about the same as a comparable Eaton 18-speed manual transmission with twin countershafts, and is far less than the heavy-duty triple countershaft Mack manual.

Dean says that the mDRIVE always seems to pick the proper gear no matter how fast or slow he drove, or whether he is on undulating or flat terrain.

“It just seems to get it right every time.” There are three operating modes – Easy Shift, Enhanced Construction, and Heavy Haul – and the Slingo machine has the heavy haulage setting, meaning shift points are a little higher on the tachometer than the Easy Shift. The settings can be programmed by technicians at the Mack service department to suit customer needs. There is the dash-mounted selector included a ‘Perf‘ (for performance) button, which delays upshifts and adds power and torque as engine revs rise, making a truck noticeably livelier during acceleration.

Dean explained that it was especially effective as the transmission reached higher gears and road speed climbed. Punching the ‘Perf‘ button again returns the transmission to an economy mode. Both he and his drivers like this feature.

“One of our drivers who has been with us for the past decade said, ‘I‘d sooner have one with a gear stick‘ when the first mDRIVE Trident arrived,” Dean said. “However I persuaded him to have a go, and needless to say, I reckon you won‘t get him out of it now. “I‘m really looking forward to the 14-speed version with the creeper gears; we could certainly use that.”