How to Select A Medium-Duty Truck Transmission

Determining the right transmission for work trucks is based not only on the truck application, but also the right combination of OEM product specifications, including horsepower and torque.

March 2009, Work Truck - Cover Story

By Cindy Brauer, Lauren Fletcher, & Sean Lyden

A wide range of transmission choices are available to match to medium-duty truck engines. The final decision is based not only on the nature of the job the truck must perform, but also on the specifics of manufacturer and upfitter products, including horsepower and torque. 

The following considerations can help guide the transmission selection process. 

1. Application.

The truck's function must be clearly identified. Factors include the amount of stopping and starting, city versus highway driving, off-road use, and PTO operation. Once the truck's purpose is determined, the next steps involve narrowing the transmission options to fit the function. 

2. Trailer Requirements.

Determine the gross combined weight rating (GCWR) to pinpoint which transmission is adequate to handle the truck, trailer, and payload safely. 

3. Engine Torque Rating.

Match the engine's torque rating to a compatible transmission. 

4. Body Company Requirements.

Consult the upfitter to identify specific body considerations in spec'ing the appropriate transmission. 

5. Driver Skill Sets.

Is the driver pool skilled in manual transmission operation or must automatics be spec'd? 

6. Manual or Automatic?

Advantages of manual transmissions include better fuel efficiency, lower initial cost, and increased shift control. Automatics offer safety, smoother shifting, and driver comfort benefits. 

7. Power Take Off.

Even if not required initially, a PTO option enhances resale value. Factors important in spec'ing a PTO in the transmission include PTO unit placement on the truck, PTO/engine rpm ratio compatibility, performance requirements, and PTO functionality. 

8. Wide/Close Ratio.

The truck application and operating conditions determine which transmission ratio is required. 

For more on selecting work truck transmissions, visit the Work Truck Web site, www.worktruckonline.com/Article/Story/2007/03/. Click on "Eight-Questions-to-Consider-when-Selecting-Medium-Duty-Transmissions." 

Truck Transmission Overview 

Aisin  

Aisin transmissions are used by variety of truck manufacturers, including GM, Ford, Toyota, Chrysler, Mitsubishi Fuso, and Hino. 

The Aisin RWD 5-speed automatic transmission for medium-duty trucks features: 

  • High torque capacity, driveability design for operator comfort with minimum fatigue, and low fuel consumption.
  • Two-mode driving, either "Economy" or "Power."  

Aisin also offers the A465 heavy-duty six-speed automatic with double overdrive, featured in Isuzu N Series low cab forward trucks. 

Allison  

Another major player in medium-duty transmission manufacturing, Allison's products can be matched to a wide range of OEM truck engines. Allison automatic transmission lineups include:

  • Highway Series (1000-4500 HS), designed to meet the horsepower needs of on-highway vehicles,19,500 lb. and greater GVW, and without a PTO option; engine hp: 300-550; torque: 550-1,770 ft.-lbs.
  • Rugged Duty (1000-4700 RDS), for vehicles operating on- and off-highway and/or requiring PTO; engine hp: 300-600; torque: 550-1,850 ft.-lbs.
  • Emergency Series (1000-4800 EVS), a complete family of transmission to meet the special  needs of fire and emergency vehicles; engine hp: 325; torque: 550-1,950 ft.-lbs. 

Eaton 

Eaton offers 250 new and remanufactured transmission models. The Eaton truck division, headquartered in Kalamazoo, Mich., produces powertrains and transmissions, including heavy-duty and synchro-mesh medium-duty transmissions. For 2009, Eaton added OEM availability for the UltraShift Highway Value (HV) 6-speed automated transmission, now offered in Freightliner, Hino, Ford, and International trucks. Eaton's manual transmissions are also featured a variety of OEM super- and heavy-duty trucks. 

Eaton Hybrid Power Systems are available on several OEMs and chassis, including International, Freightliner, Peterbilt, and Kenworth trucks. The hybrid system won the CALSTART 2008 Blue Sky Award for environmental innovation and technology. 

General Motors 

Introduced in 1939 for 1940 model-year vehicles, GM's Hydra-Matic was the first fully automatic mass-produced transmission developed for passenger automobiles. Hydra-Matic transmissions are now used in GM's trucks, including the Chevrolet Silverado and Tahoe and GMC Topkick and Yukon. 

GM also marries Eaton manual and Allison automatic transmissions to its heavier-duty models in the GMC Topkick and Silverado HD and Chevrolet Kodiak and Silverado HD lineups. 

Mercedes-Benz  

Mercedes Benz manual transmissions, used in Freightliner business Class M2 trucks, are designed for 520 ft.-lb. and 660 ft.-lb. engine ratings. Features include: 

  • Smooth, fully synchronized shifting and reduced pedal effort.
  • Synchronized transmission design that doesn't require double clutching.
  • Intuitive shift pattern for both experienced and beginning drivers.
  • Standard SAE six-bolt PTO port on the right side for easy PTO installation. 

The Remanufactured Option

Remanufactured transmissions are one cost-efficient replacement option in returning an older truck to service. 

According to Bob Boeglin, national sales manager with Jasper Engines and Transmissions, "the remanufactured brings the transmission not only to its original specs, but also includes all the most recent updates available." 

Boeglin estimates fleets typically could save 30-40 percent of a new transmission cost with a remanufactured unit, "with basically the same warranty," commonly a two-year, unlimited-mile warranty. 

A list of remanufactured transmission suppliers can be found on Automatic Transmission Rebuilders Association's Web site, www.atraonline.com.