Building a vocational truck is not unlike renovating a kitchen in an older house. It looks straightforward on paper: cabinets, appliances, wiring, plumbing. But once the walls come down, you discover load-bearing structures, outdated wiring, code conflicts, and space constraints that force constant trade-offs.

Similarly, a service body isn’t just bolted onto a chassis. Every consideration from weight distribution to the placement of tool cabinets, as well as electrical loads, axle spreads, and frame clearances interact with some other part of the system. Change one element, and three others must be reworked.

Reworking the truck after a change is a luxury most fleets don’t have. It’s far better to get it right the first time.

It’s possible today — and smart — to build the truck virtually ahead of ordering the body and chassis. Many body builders, or truck equipment manufacturers (TEMs) use CAD and programs like Load Expert or Truck Science to map out weight distribution, axle configurations and component placement ahead of production. Adjustments can be made on screen to optimize the spec’, and to determine if a given body will fit your chassis of choice.

If up-to-date CAD drawings are available from the OEM, placement of aftertreatment system components or fuel tanks can be accounted for up front, rather than when the truck arrives at the upfitter’s facility.

“You can build the truck virtually in these programs, and it will look just like complete vehicle,” suggests Jeremy Harrower, manager of technical programs at the Canadian Transportation Equipment Association (CTEA), a group representing upfitters, trailer makers and body builders. “You can put all the components on, put the body on, and then see what happens when you adjust dimensions, etc. From my perspective, the best approach is to talk to the body builder first. Since that’s the critical piece of equipment, the upfitter can recommend a couple of manufacturers and potentially a couple of chassis that may work from each manufacturer.”

What could go wrong?

As William Shakespeare once famously wrote, “There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.”

Installations such as dump bodies can be relatively straightforward, most of the time, but when you get into complex chassis with PTOs and auxiliary axles, etc., the potential for calamity increases exponentially.

Nicolas Picard, dealer technical manager at Excellence Peterbilt in Sainte-Julie, Que., recalls a situation in which the body installer, unfamiliar with the truck’s aftertreatment system, rerouted the exhaust stack to make room for a second steer axle.

“It was a retrofit, not an original installation, but we had a customer come back three times complaining about a failed NOx sensor,” he told trucknews.com. “Rainwater was running down into the rerouted exhaust stack and contacting the NOx sensor. They are expensive and they are very sensitive to water. That problem could have been avoided if the installer had asked us how to work around that auxiliary steer axle.”

Picard described other instances in which the body builder was installing one or more PTOs on the truck. First, there are differences in the electronic architecture between, say, a Cummins engine with an Allison transmission and a Paccar engine with a Paccar transmission. And there are several engine models and ratings to choose from — all with unique requirements. That’s on top of the customer’s requirement for a cab-controlled PTO throttle or a remote-controlled throttle.

In less dramatic instances, there could be limits to the vehicle’s wheelbase or axle placement options imposed by the body configuration. In a bad-case scenario, this could limit the vehicle’s allowable gross weight. Or in a worst-case scenario, it could throw off the body builder’s vertical center of gravity calculations, ultimately affecting stability in the field.

Or, oops, we can’t have any crossmembers here because the body builder needs that space for a big pump. This is why communication in advance of the build is so important.

When something goes awry, there’s usually a lot of finger-pointing before everyone gets down to fixing the problem, but a lot of the liability can fall on the dealer who sold the truck, even though it’s not necessarily their fault.  

Take the example of a customer who buys a stock truck — or even a used truck — for their application to reduce cost, only to discover after the fact that it won’t accommodate their body. And yes, that happens.

Or if the body builder doesn’t provide the truck dealer with accurate finished weights of their bodies. How is the dealer going to ensure the finished weight, once the body is installed and loaded, is going to put the right percentage of load on that front axle, for example?

“Every time you have somebody that wants a dump box that’s a foot longer than what we normally do for stock, everything changes,” said Jamie Impola, account manager at Rush Truck Centres in Kingston, Ont. “It changes where the crossmembers need to be and the weight distribution, too. People often want to take this box or this body off this truck and put it on that chassis. Before you know it, you can get into a real mess.”

“If it’s a stock unit for a dump truck or something fairly simple, it’s usually a lot easier than dealing with a utility body,” said Shane Bosch, president and CEO, Glover International Trucks in Calgary, Alta. “There have been cases where we’ve had to extend or shorten wheelbases. That’s expensive and it’s a huge liability. That’s the reason we get the customer and the body builder talking first to make sure everyone in the transaction is on the same page.”  

Don’t touch that wire!

The latest wrinkle in the struggle to build the perfect vocational truck is multiplexing. Though not exactly new, some of the smaller truck equipment makers haven’t yet come up to speed on electronic controls.

In a multiplexed wiring environment, a single wire can carry several signals. These are connected to various electronic control modules on the truck, and they all communicate quite successfully. Generally, multiplexed circuits replace physical wires and switches.

“We need to use the OEM PTO switch in the dash rather than the traditional wiring method because many of the components on the truck need to talk to each other,” Picard said. “All that communication is now handled internally.”

And everything works fine until a worker cuts into a wire, because that’s the way they’ve always done it.

Sean Whelan, a Mack vocational sales manager at Vision Truck Group in Cambridge, Ont., has been selling and building vocational trucks for 37 years. He says Mack still uses a 9-pin connector, though a multiplexed environment is coming.

“That was the standard for years, but it’s changing and body builders will have to change with it,” Whelan said.

In fact, each of the major truck manufacturing groups have developed proprietary multiplex architecture. That means the interface between the body and the chassis may be different across the brands. Body builders will need to get up to speed on that, as many already have. It’s been about for about five years now.

All the OEMs offer courses for body builders, and some even offer engineering access to the spec’ing and programming process, which is more useful than watching even a full season of DIY shows on Netflix before tackling your kitchen renovation.