Manual Transmissions Are Still The Rule
Tom Berg
Equipment Editor
What are your vehicles packin' for gearboxes these days? Ten-speed models for the heavy tractors and 5- or 6-speeds for medium trucks? Then you're on a well traveled road, because those are the most-often spec'd manual transmissions in the biz, according to the builders.
And if you're reluctant to take the plunge to automatic or automated mechanical transmissions — at least in Class 8 trucks and tractors — you're also with the overwhelming majority. About 90% of today's heavy duty vehicles are built with manuals, though that majority is shrinking by about 2% a year, says Bill Batten, Eaton's Roadranger product manager. He sees its AutoShift and UltraShift automated models gaining ground. Eaton's Lightning manuals are hybrids, because drivers shift with a lever but don't have to double-clutch. Electronics can synchronize gears by revving and slowing the engine.
Eaton's main competitor, ZF Meritor, reports that 75% of its transmission shipments are manuals and the other 25% are its FreedomLine automated mechanical product. Charlie Allen, director of sales and engineering, agrees that automated models will only become more popular. Both companies make both types of transmissions, so they're happy to sell you all the manuals you want for now.
Among midrange trucks, automatics have a much stronger following — mainly because many middies tend to run in stop-and-go traffic. In Classes 5 through 7, automatics account for more than half of sales overall, and will grow as more "two-pedal" automated products come to market. In Class 4 and lower, manuals are unusual, which explains why the market for ZF North America's six-speed manual — available in Ford and General Motors diesel-powered pickups — is limited, says Wolfgang Schmid, director of marketing and communications.
Eaton is in first or second position for manual-transmission availability at most North American builders of Class 5 through 7 trucks, so Batten has a good view of what's going on there. He says the 6-speed manual has all but replaced the "5 and 2" — the 5-speed manual with 2-speed rear axle setup that was popular a decade and more ago (just as 5-speeds replaced the "4 and 2" years before). Seven-speed manuals that gained some sales in the '90s have likewise gone out of style in favor of the cheaper and easier-to-drive 6-speed.
6-Speeds Are Neat
A 6-speed has enough ratios for most anything a medium-duty truck will encounter, but a 5-speed might not. With all respect to customers, Batten notes that the midrange truck market is very price-sensitive. "Most everybody should buy 6-speeds," he says, "but some think they can save a hundred bucks [per truck] so they buy a 5-speed." A 5's top gear is direct, so the engine might be straining at highway speeds, and if the axle ratio is made faster (numerically lower), startability might not be as good as it should, and the clutch can get beaten up.
Those willing to spend the money for a 6th gear sometimes take advantage of 6th's overdrive ratio by mating it with a "slow," numerically high axle ratio; this turns 1st gear into a "creeper" for starting out on steep upgrades or maneuvering in tight quarters. The normal start-out gear then is 2nd. With a faster axle ratio, 1st gear should be used to start out in most circumstances. Of course, a tractor based on a midrange chassis will endure higher gross weights and will need an 8-, 9- or 10-speed.
Direct Versus Overdrive
Some engineers and fleet managers seem to enjoy debating the argument over a direct-drive top gear versus overdrive. Most heavy transmissions have overdrive or double-overdrive so engines can propel the vehicle at high road speeds and stay in their most economical operating range.
But a direct-drive top gear and a "fast" (numerically low) axle ratio can let the truck achieve the same road speeds, according to proponents. Moreover, overdrive gearing introduces a bit more friction and lube "churning," which saps a bit of energy. Advocates of more efficient direct-drive gearing say this costs money in fuel — usually 1 to 3% more.
Nonsense, say overdrive fans. The loss in efficiency is so small that it cannot be measured in tank mileage except under the most controlled conditions. Everyday traffic congestion and driver habits influence fuel economy far more. And an overdrive transmission sends less torque through the driveline, which can extend shaft life. Yes, the driveline spins faster, so U-joint angles must be as low as possible, but this is easily designed.
And so the debate can go on. But it's seldom a loud one, because both direct and overdrive transmissions do a fine job if they — and all other driveline components — are properly spec'd.
Heavyweight King
In heavy highway tractors, the 10-speed has replaced the 9 as the most popular model because 10s do a better job of ratio coverage — providing enough "steps" to get the truck up to speed and keep it there, according to ZF Meritor's Allen, who says that his firm has accordingly dropped its nine-speed models. The 10 has also replaced some 8-LLs, 13s and 18s because today's engines have wide operating ranges and simply don't need more than 10 speeds, he adds.
Though a high-capacity 18 is commonly chosen for use with Big Power diesels producing hefty torque, Meritor has Torq-2 versions of its 10-speeds with 200 pounds-feet more capacity in 9th and 10th gears, where an over-the-road tractor spends most of its time. So in some applications that 10-speed might suffice, Allen contends. This would save some serious purchasing dollars, with some truck builders charging a big premium for an 18-speed.
Eaton also has models that are stronger in cruising gears. These can be rated at an extra 100 pounds-feet in the top two gears. But Eaton's Batten says neither they nor his competitor's 10-speed models are any substitute for an 18-speed, with its high capacity (enough for 2,050-pounds-foot diesels), great flexibility, pleasurable driving characteristics and high resale value.
Spicer has just announced a Pro-Shift 18, and it's already at work in road trains in Australia, says Jim Averill, marketing manager for Transmission Technologies Corp. It's rated at 2,050 pounds-feet, like Eaton's Roadranger 18, and engineers are mulling the idea of uprating it to as much as 2,400. But you'd have to special-order the Spicer in trucks made in the U.S. or Canada, because TTC (jointly owned by Dana Corp. and Desc SA de CA of Mexico) lost out in component "rationalizations" done by truck builders in recent years.
Spicer transmissions were once standard at International, but Eaton got that business. TTC builds its Spicer-brand products in Mexico, a comparatively small market, and that's where its North American sales are now limited, Averill laments. Maybe the new Pro-Shift 18 will find some appeal among Yanks and Canadians, and give Eaton some competition in the high end of the manual-gearbox market.
Vertical Integration
Several years ago, International also removed Spicer medium-duty products from its Next Generation midrange trucks, again giving the business to Eaton. At the time, International proudly announced that it had slashed the number of possible engine-transmission combinations in its new 4000 series from more than 800 to around 70 — and even that was more than enough to equip any truck to accomplish its hauling task.
Transmissions are among the component types that all truck builders have looked at critically. To cut engineering and sales costs, builders drastically pared their parts lists throughout the '90s and into the '00s, so customers find far fewer spec'ing choices. Some say this is an example of vertical integration, even if truck builders don't actually manufacture the products they choose to offer.
One builder that is increasingly vertically integrated is Freightliner LLC, which has standardized on Mercedes-Benz medium-duty transmissions from its corporate parent for its Freightliner and Sterling midrange trucks. Exceptions are automatic or automated models that are standard in most Sterling Acterras, but buyers wanting manuals will get M-Bs unless they opt for Eatons.
Mack, the original vertically integrated American truck, nonetheless sells many Eaton Roadrangers in its highway models. Mack's beefier and more expensive Maxitorque gearboxes tend to be sold in construction trucks. Over the years, certain Maxitorques have offered multi-speed Reverse capabilities; these allow drivers to back briskly to sometimes distant pavers and pour sites whose confines are too narrow for trucks to drive to, then turn around to unload. Older models provided a separate shift lever for Forward and Reverse; today's products use a thumb switch, so drivers can also maneuver the truck fore and aft without moving the main lever.
While most engines have wider operating ranges, Mack also has an exception. Its latest Maxidyne with internal EGR has a narrower rev range. This requires at least one more ratio in the transmission, so Mack has made a 6-speed standard where a 5-speed used to suffice. Also affected is axle gearing, with the Maxidyne's operating range several hundred RPM higher, which makes less torque at clutch engagement RPM. Startability is preserved by adjusting the axle ratio, and designing all the Maxitorque transmission's ratios to limit engine revs at highway speeds, as well.
Torque Rules
Aside from the number of gears, the primary factor in transmission spec'ing has always been torque capacity. This has to be high enough to handle the diesel's output, as well as any uprating that an owner may have in mind for the future. Electronic engine controls allow punching up a diesel's output to pull higher loads or, more likely, to give a used truck more resale appeal. Of course, today's electronics also allow raising horsepower while limiting torque, so the original smallish driveline might still be sufficient.
Yet any engine's highest attainable rating should be accounted for when spec'ing the driveline. The engine might produce 1,450 pounds-feet for its first owner, but could be boosted to 1,550 later, so the higher output is what the driveline should be built for. This is a cheap option, and should more than pay for itself through higher resale value made possible by the truck's stronger and more desirable engine.
Owner-operators have always favored Big Power, and so have proprietors of "premium" fleets who want to attract and retain good drivers. Horsepower/torque ratings leveled off somewhat during the recent recession — an almost unnoticed trend that was eclipsed by the serious sales slump. Drivers had to be content just keeping decent jobs. But prosperity is returning and with it a driver shortage. To compete for drivers, stronger engines may be necessary.
"Torques are creeping up," reports ZF Meritor's Charlie Allen. "There are now more 1,550 and 1,650 [pounds-foot] engines," and transmissions thus have also gotten beefier. "Once the new EGR engines are proved reliable — and they seem to be already — torque will go up again. Or, customers might remember they were able to move freight with 1,450, 1,550 and 1,650 engines."
For midrange trucks, Eaton now offers a Robust Transmission System for its Synchro 6 models, Batten says. The system includes stronger, longer lasting synchronizers; enhanced seals to retain lubricant and reduce possible internal damage; and a self-adjusting clutch to save considerable maintenance money. In addition, an extended warranty is available at a reduced price.
Extended Warranties
Transmissions today last many miles longer than those of yesteryear. Like the diesels they work with, many midrange gearboxes go 400,000 to 500,000 miles, and heavy duty models will go to 1 million miles or more. That's why manufacturers can offer warranties that cover about two-thirds of their transmissions' expected life. Warranties usually are predicated on use of synthetic or semi-synthetic lubricating oils. The builders publish lists of approved lubes, so buyers should be sure that their gearboxes get only those products. Otherwise the warranties may be blown, along with the transmissions.
