5 Key Questions When Spec'ing Transmissions

If you’ve been spec’ing the same manual transmission for a while now, it’s time to take a look at new options. Today’s transmissions offer smart features designed to improve performance, fuel efficiency, safety and productivity, says Gerard DeVito, chief technology officer for Eaton’s Vehicle Group.

“Features like predictive cruise and predictive shifting help the transmission perform seamlessly for the driver, using look-ahead technology to execute shift decisions that improve fuel economy and driver comfort,” he says. “These drivability improvements can help with driver retention and recruitment. Advances in automation make this possible.”

With choices like these becoming more plentiful, it is essential for fleet managers to determine which options make the most sense for their applications. The benefits of spec’ing the right transmission for the job include fuel savings, reduced maintenance, and less driver fatigue, says Brian Daniels, manager of Detroit Powertrain and Component Marketing for Daimler Trucks North America.

Based on conversations with transmission makers, here are five considerations to think about when spec’ing transmissions.

1. Direct or overdrive?

Carl Hergart, director of powertrain and advanced engineering at Paccar Technical Center, says the choice between direct or overdrive comes down to application, route, payload, and vehicle speed. Historically, he explains, there was a significant difference in efficiency between a direct drive and an overdrive gear, which led fleets to prefer direct drive at lower speeds, with lighter loads on flat terrain. 

Direct drives are efficient because “their top gear is one to one,” explains Scott Barraclough, technology product manager for Mack Trucks. “That is the most efficient way to operate a transmission. You have less parasitic losses to the transmission, so you can see about a 1% fuel economy increase for a direct drive.”

But with recent advances in gear efficiency, Paccar’s Hergart contends that there is no longer a substantial difference between direct drive and overdrive. “That’s backed by what we’re hearing in the field. Customers are telling us they prefer overdrive to direct drive,” he says. 

Eaton’s DeVito agrees that today’s overdrive models are as efficient, or nearly as efficient, as direct drive. “In the vast majority of North American duty cycles, overdrive provides the optimal balance of performance and fuel economy,” he says.

But, because there are still scenarios where one option performs better than the other, OEMs continue to offer both.

“Usually, direct drive is great,” says John Moore, product marketing manager – powertrain for Volvo Trucks North America. “If you’re running 65 mph or less, super direct drivelines are providing efficiency at even faster speeds. But overdrives give you a wider range at higher speeds.”

Overdrives also offer a wider range of ratios with heavier axles. If a truck has a 52,000-pound rear axle, for example, it would be difficult to find a direct drive ratio for that weight. In this case, a fleet would be forced into an overdrive transmission.

“Rear axles are starting to catch up,” says Barraclough. “Manufacturers are coming out with ratios in the mid to lower two ratios, like a 2.47, 2.28 or even down to a 2.15 (to 1). Those ratios allow you to work with the direct drive transmissions operating at higher road speeds of 65 to 70 mph, while keeping the engine running efficiently.”

2. Manual or automated?

Fleets have a choice of three types of transmissions: Manual, automated manual (AMT), and automatic. Manual transmissions are often preferred due to their simplicity, reliability and low acquisition cost. However, a shortage of skilled drivers has led fleets to shift from manual transmissions to automatics and AMTs. And Eaton Cummins and Paccar call their new transmissions simply “automated,” rather than “automated manual,” noting that they were designed from the ground up as automated models.

Automatic and automated transmissions benefit fleets in many ways. New drivers catch on quickly, because driving a truck with an automated transmission is a lot like driving a car – you put it into gear and go. “It keeps their eyes on the road, reduces distractions, and lessens the fatigue associated with manual transmissions,” says DTNA’s Daniels.

Automated and automatic transmissions also can save a fleet money in the long run by offering consistent performance, fuel economy, and reliability across duty cycles and driver skill levels.

With automation, drivers no longer need to think about gear they are in or the proper shift on a grade.  “Automated manuals work well in downspeeding applications. You can’t use a manual in those situations because the engine speeds are too low; the driver would be shifting too much and, in some cases, not shifting fast enough,” Moore says. “An automated manual knows when to downshift and it does it quickly, so the driver doesn’t need to be concerned about it.”

The fuel savings in this situation could easily be 10% when comparing extreme downspeeding with AMTs to older conventional drivelines with manuals, he adds.

Nevertheless, Christian Fieldhaus, senior project manager of sales for ZF, reports there is still a case for manual transmissions. He notes trucking remains a very price-sensitive market, so some companies may not want to invest in a pricier automated or automatic transmission.

DeVito agrees. “Fleets still spec manual transmissions when trying to save money, when they have an experienced driver pool, or when they have a technically challenging application, such as a heavy haul or wrecker service, where the driver needs to be in complete control.”

Though there are niche applications where manual transmissions work best, Barraclough says, “Those applications are starting to dwindle. Automated or automated manual transmissions, such as the [Mack] mDrive, can now work with a split box transmission on a pump or vacuum truck. We could not put the mDrive on this application until this year. So, while there are still heavy haul applications where a manual is still needed, I suspect it’s only a matter of time before these situations are solved.”

3. Shifter developments

Fleets have three shifter options for automated and automatic transmissions: A physical shifter between the seats; a dash-mounted, push-button shifter; and a column-mounted shifter.

Detroit has put its shifters on the steering column and incorporates engine brake controls into them. Drivers no longer must locate a separate gear shifter, brake controller and brake actuator while driving. Paccar also offers a column-mounted shifter, which Hergart says provides an “intuitive handshake between the driver and the powertrain, with easy access to engine brake, shifting and transmission states. This maximizes driver comfort and eliminates the need for drivers to take their eyes off the road [to shift].”

Moore says Volvo has opted to add a shifter to the dash, because steering columns are already riddled with controls. He explains, “We want the transmission to just do its thing. We don’t want drivers messing with it. Putting it on the dash gets the shifter out of the way but keeps it within reach.”

4. Telematics and transmissions

“Vehicle connectivity and telematics are becoming ‘must haves’ for fleets, because it can significantly reduce unplanned downtime,” says DeVito. Eaton IntelliConnect remote diagnostics offers near real-time monitoring of vehicle fault codes, action plans for those fault codes, and customized reporting.

Paccar has made remote diagnostics capabilities standard on its products, allowing continuous monitoring of the powertrain. Mack Trucks has done the same, monitoring its transmissions with its GuardDog Connect telematic system. Allison’s connected capabilities, which are backwards compatible to Allison fourth-generation electronic controls, provide insight into more than 170 different transmission conditions.

Telematics is now viewed as the gateway to the truck. Sensors monitor how well the transmission is performing. If there is a problem, a trouble code is transmitted to a central location. With this trouble code in hand, manufacturers can determine the health of the transmission and communicate that prognosis to customers, who can arrange for service before a breakdown.

“An ounce of prevention is worth a pound of cure,” Moore says. “We can actually see the issue before it becomes a huge problem, and in many cases, stop a tow from occurring.”

Volvo also has begun connecting transmissions with roads and landscapes, so telematics can inform the vehicle which hills it is climbing in advance. Volvo’s I-Shift uses intelligent electronics to continuously monitor grade, speed, weight and engine load, shifting when necessary or holding a gear – whichever saves more fuel.

“It gives the transmission eyes to see what’s coming so it has a better ‘idea’ of when to shift or downshift, when not to downshift,” Moore says.

5. Remanufactured transmissions

Remanufactured transmissions can be a good choice for a fleet looking to save money.

The expectations of a remanufactured transmission are that it will last another lifecycle. That capability is delivered through quality of work and attention to detail. For example, Detroit Reman Transmissions are completely disassembled, thoroughly cleaned and carefully inspected, and all wear items are replaced and assembled with dedicated tooling, fixtures and gauging. They are then tested to ensure they perform according to specifications.

However, DeVito warns, “There are many imitators in this space, and it can cost a fleet in the long run.” For this reason, top transmission manufacturers recommend asking the following when buying a reman transmission:

• Does the remanufacturing process bring the transmission back to current OEM specifications?

• What is the standard warranty and is it transferrable?

• Is service coverage provided nationwide and is labor covered?

Knowing the answers to these questions will ensure fleets get a reman transmission that will stand the test of time, and if there is an issue, there is a support team in place to care for the product after purchase.

Ronnie Wendt is a freelance writer based in Waukesha, Wisconsin.