In the wildly successful U.S. truck market, there are new models and technologies coming out at an astonishing rate. It’s important to look at this market and examine the profit potential it has for the transmission rebuilder.

Trucks have historically been classified into three broad groups: light duty, medium duty, and heavy duty, based on gross vehicle weight and payload capacities. Light duty trucks include the sport-utility vehicles, vans and pickups. Pickups and vans are broken down into category by GVW, giving us half-ton, three-quarter-ton, and one-ton vehicles. Medium duty trucks are large, straight-chassis vehicles, which usually fall into the class five and six range. Heavy duty includes class seven and eight vehicles, which are usually 10-wheel, straight-chassis trucks and over-the-road tractor-trailer combinations.

Sport-utility vehicles have enjoyed tremendous growth and popularity with drivers for the last decade, and the trend continues. A less-noticed change is the trend toward heavy duty pickup trucks. "Heavy duty" light trucks seems to be an oxymoron, like jumbo shrimp, but the major truck manufacturers—Dodge, Ford, and GM—are all producing bigger, heavier capacity pickups. The three-quarter and one-ton pickups are being offered with larger displacement gas and diesel engines and increased GVW ratings. All this power and heavyweight hauling has produced some heavy duty truck transmissions which we are going to review.

A few years ago, the heaviest duty pickup trucks had four-speed transmissions. The NP435, Muncie SM465, and the Borg Warner T-18 and T-19 models were the units of choice for one-ton trucks. Enter the late 1980s and the specter of EPA emissions and mileage regulations extending beyond passenger cars to light trucks, and the designers set about creating new heavy duty transmissions for these vehicles.

The Getrag 360
This 5-speed, cast-iron case transmission appears in Dodge trucks with the 5.9 diesel engine, from 1989 through 1993. This design suffered from being under "spec’d" for the motor it was mounted to, and has the dubious distinction of being the most expensive unit to repair of its era. An overhaul kit sells for $750, a cluster gear for $1,100, and list price for a new unit is $3,875. Most owners of these vehicles opt for installing an NV4500 in its place after fighting durability problems. This unit features helical gearing, with all forward speeds synchronized and in constant mesh.

The NV4500
This is a 5-speed, cast-iron case, top-loading transmission, used by GM and Dodge in their heavy duty pickups (figure 1). It’s a serious truck transmission that uses some innovative designs. The NV4500 is found behind gas and diesel engines, and is produced in two- and four-wheel drive configurations. Using helical gearing with all speed gears in constant mesh and all speeds synchronized, this transmission will handle 450 ft-lbs. of torque, and vehicles with a combined gross weight of 19,000 pounds. The 4500 uses a dual cone synchronizer for first and second gears, similar to the familiar, world-class T5 design (figure 2).

The 1–2 synchronizer also has a set of spring-loaded flyweights in the synchro hub that govern shift speeds, to prevent overrevving the motor on a 2–1 downshift (figure 3). The 4500 weighs in at 195 pounds dry, and has a lube capacity of 8.5 pints of Castrol Syntorq synthetic gear lube. Two ratios are currently available (figure 4).

The 4500 is a serious truck transmission with a simple, easy to work on design. New Venture has the capability of adding a sixth speed to this design. The ability to have gas and diesel engines geared low enough for serious pulling power and having one or two overdrive gears for fuel efficient cruising is a necessity for today’s market. 

ZF S5-42 and S5-47
Ford introduced the ZF S5-42 transmission in 1987. The ZF S5-42 is an aluminum case five-speed transmission, with integral bell housing, all-speeds synchronized and in constant mesh (figure 5). Available in two- and four-wheel drive designs, this unit is found behind 4.9L, 5.8L, and 7.5L gas engines and the 6.9L, 7.3L, and Direct Injection Turbo diesels. Figure six illustrates the break down of the model number S5-42.

The ZF units use compound lined synchro rings and are lubed with Mercon ATF or synthetic Mercon ATF.

There are two ratios available: close and wide. The wide ratio unit is available for all F-series trucks over 8500 lb. GVW and all engines with the exception of the F-Super Duty commercial stripped chassis powered by a diesel engine. The close ratio version is used behind the 7.3L diesel in F-series trucks with a GVW of 8500+ lbs. It is crucial to match model numbers when swapping transmissions, as a ratio mismatch will make the vehicle undriveable (figure 7).

In 1996, Ford introduced heavier and more powerful pickup models and ZF upped the design level of the gearbox to the S5-47. The break down of this model number is illustrated in figure eight.

To handle the increased torque loads, the case was cast with heavier ribbing and new ratios have been provided (figure 9).

The S5-47 models use Mercon ATF and Synthetic Mercon ATF for lube. The S5-42 and S5-47 transmissions appear to be similar externally, but none of the internal parts are interchangeable.

Coming soon to Ford dealers for the 1998–99 season will be an even heavier pickup truck that will have a new ZF transmission: the S6-65. If the usual model number breakdown applies to this gearbox, it will mean a synchronized six speed transmission with a torque rating of 650 ft-lbs.

The S6-65 is the first light duty gearbox to have its own internal pump, plumbed to an external cooler to reduce operating temperatures. This new unit will be able to handle vehicles with up to 28,000 pounds GVW, so the heavy duty light truck just got heavier. Information on this unit will be released as it becomes available.

The endless changes occurring in transmission models and designs may be confusing, and the horizontal growth of inventory may be expensive, but these conditions provide us with one benefit: job security.