It’s been two years since we first reported on a drive of an early Allison TC10 automatic transmission. Since then, the innovative product has undergone more testing and development and has entered production at Allison’s plant in Indiana. The time it took to get it exactly right allowed competitors to field new or improved automated transmissions, but the TC10 stands out as the only true multi-speed heavy-duty automatic.

So far, the TC10 is available from only one builder, Navistar. You can buy a TC10 today in the International ProStar, which represents the exact type of vehicle the transmission is aimed at: short- and regional-haul tractors that run on-highway but see a lot of gear shifting, as well as some vocational tractors that don’t go off road. Its fuel economy advantage over manual and even some automated gearboxes, said to be a solid 5%, would make it valuable in long-haul tractors, as well.

“TC” in the name means Torque Converter and Twin-Countershaft gearbox, as the product has both. The combination provides very smooth start-ups, and quick shifting that’s done under continuous power flow — “power shifting” similar to fully automatic Allisons and other lighter-duty truck products. Power flow in the TC10 alternates among the counter- and main shafts, depending on what gear it’s in, Allison reps explain. The TC10 has no dry clutch that contacts the flywheel, but it does have wet clutches — five in the main 5-speed gearbox and two in the 2-speed range box. The range box also uses planetary gears and a synchronizer.

The resulting feel is like an automatic transmission, but with less “slush.” There is inherent smoothness that competitors’ automated manual products can’t quite match, advanced though they are. They definitely can’t duplicate the Allison’s continuous power flow, because they need a pause in engine output to make each gear change. Allison says that pause requires an engine to work a little bit harder each time to regain momentum, and that costs fuel.

Customers’ actual operations will determine if that difference converts to better tank mileage, but it does make for rapid acceleration. Power, weight and other factors being equal, a TC10-equipped truck will outdrag one with an automated manual, and will leave a rig with a manual transmission way behind.

In a fair comparison, a driver can definitely feel a TC10’s smoothness and acceleration advantage. Recently, as a guest of Navistar at its Melrose Park, Ill., engine facility, I drove three International ProStars. Two had well-behaved Eaton products (one was a 16-speed UltraShift and the other a new Advantage automated 10-speed). I drove these, and another tractor with a TC10, on city streets and a short stretch of Chicagoland expressway.

The gross combination weights of the three rigs were similar, in the mid to high 70,000-pound range. The Eaton automateds changed gears smoothly, but the Allison was smoother. Its gear changes are muted and sometimes imperceptible, especially in the higher gears.

For a driver who wants to know what the transmission is doing, a readout on the Allison’s keypad will tell him, as it did me. For instance, 10/1 means 10 gears are available and it’s about to start out in 1st, or 10/9, that it’s in 9th-direct and any time now will upshift to 10th-overdrive.

The “shift-it-himself” driver knows there is joy in feeling the power course through each gear and satisfaction in making those changes all by himself, assuming he does it correctly every time. However, very few drivers can, especially when they tire out and start missing shifts, overrevving the engine, and wasting fuel. That’s why automated transmissions are catching on in heavy trucks, although with most you can still feel the power being transmitted mechanically.

Another Look

A few weeks earlier, I took another TC10-equipped ProStar on a longer jaunt out in the countryside. A couple of Allison marketing people rode along as we departed from Indianapolis via Interstate 65, cruising south to Indiana 46, west to Bloomington and Indiana 37, then north and back to Allison’s premises. Highway 46 has some short but steep hills that begin at Nashville, a touristy town in scenic Brown County, so it’s a good test of an engine’s power and a self-shifting transmission’s ability to pick the correct gear for a situation.

From a dead stop, the TC10’s torque converter launched the vehicle authoritatively. The converter multiplies torque to increase the effectiveness of 1st gear’s otherwise tall 7.4:1 ratio. The converter locks up right away to boost efficiency all the way to cruising speed. Ninth gear is 1:1 direct and 10th is a 0.86:1 overdrive. Rolling terrain caused the transmission to shift often between 9th and 10th, but usually I didn’t notice unless I looked at the selector’s LED readout.

Thanks to load and incline sensors on the chassis, its Generation 5 electronic controls and careful matching to those of a 12.4-liter, 475-horsepower Navistar MaxxForce 13, the TC10 always seemed to know what to do, and did it well. I played around a little with the selector’s up- and down-arrow buttons to effect up- and downshifts, but mostly I left it alone.

This was not much of a pull because the short Vanguard demo trailer wasn’t heavy. Our GCW was about 56,000 pounds, but sometimes equipment that’s not sorted out will not work well under light loads. But this powertrain worked very well together. Shifts were smooth, though I did feel a thump or two under moderate throttle conditions. It was nothing objectionable, but maybe some tuning was in order, because I didn’t feel any thumping in the other ProStar up in suburban Chicago.

Applications For the TC10

The TC10 will not replace Allison’s traditional 6-speed 4000 and 4500 RDS (rugged duty series) automatics that see on/off-road service in straight trucks. The 4000 HS (highway series) works well for some heavy on-highway applications but is not a good fit for long-haul road tractors, Allison people acknowledge. This is where the TC10 automatic can come in.

Only Navistar currently offers the TC10. While it also sells Eaton automated and manual gearboxes and Allison’s traditional automatics, it doesn’t have a proprietary automated transmission, so the TC10 fits nicely. Steve Gilligan, Navistar’s vice president of product and vocational marketing, says the TC10 is priced at 15–20% more than Eaton UltraShift products, which in turn are $4,500–$6,000 more than comparable manuals.

Allison people say they’re talking with other builders about adding the TC10 to their options lists. A good prospect might be Paccar, owner of Kenworth and Peterbilt, which also does not have a proprietary automated or automatic transmission. Paccar partners with Cummins and Eaton for several products, and, of course, offers 5- and 6-speed Allisons in medium-duty trucks and heavy vocational models, so adding the TC10 might be a logical step.

Less likely to bite on the TC10 are Volvo and Mack, which have their own I-Shift and mDrive automated gearboxes (but do offer traditional Allison automatics). Volvo also uses UltraShifts on a limited basis, but both brands prefer to sell their own powertrain products. Daimler has its own DT12 automated transmissions as well as UltraShift options, but Freightliner, its volume brand, has shown willingness to offer vendor components, so maybe it’ll give a nod to this Allison product.