Common Problems With Allison Transmissions (According To Owners)

Allison Transmission has been an integral part of America's automotive technology with a long resume specified by more than 200 auto manufacturers. This age-old transmission company has played a big role in most propulsion industries, including aviation, motorsports, construction, and transportation. Today, popular nameplates under General Motors — like the GMC Sierra and Chevrolet Silverado — run engines paired to an Allison 1000 transmission.

Allison Transmission also developed the first fully automatic transmission for heavy-duty applications in the United States. The transmission company has been involved in hybrid technology since 1966, contributing to the advancement of hybrid-electric systems technology and the development of fully-electric axles. 

Despite their long resume powering a list of popular nameplates in the automotive industry, Allison transmissions can have problems. Based on the experiences of vehicle owners with Allison transmissions, issues often arise from TCM module problems, limp mode, or an improper hookup. Fortunately for owners, Allison offers a standard limited warranty on their transmissions that fully covers labor and parts, depending on the mileage and model.

If you own an automobile running an Allison transmission developed between 2004-2008, and it is presenting transmission issues, the culprit could be a faulty TCM module. A Technical Service Bulletin (TSB) was issued on these transmissions, and chances are your unit might not have been serviced. TCM module issues on transmission systems can cause performance and shifting issues, with the most common symptoms being delayed or erratic gear shifts, stuck gears, or difficulty switching between gears.

The Allison 1000 model features a failsafe feature known as "limp mode." When triggered, the vehicle's transmission locks in third gear. Limp mode is activated to protect the transmission from breaking down. When this happens, you'll likely get a check engine light and a P0700 code, which is a general GM code for transmission issues. In most cases, limp mode is triggered by overheating or excessive loading — it could also be triggered by low transmission fluid as well. 

Improper hookup is a minor but common problem with Allison transmissions as well. If the transmission is not hooked up correctly, it could cause erratic shifts, fault codes on the dashboard, and even transmission failure. Visually inspect all parts connecting to the transmission system for breakages, including electric wiring. Also, check if the vacuum lines are hooked up correctly. Fix anything that seems odd and test to see if the transmission issues persist.

Allison transmissions are widely used in medium and heavy-duty transmission systems. They are known to have zero power interruptions between shifts, making them ideal for powerful engine applications. Still, anything mechanical needs proper care. 

Maintaining an Allison transmission means owners need to keep up with fluid changes, especially if the vehicle is used for towing or heavy tasks. Low fluid will cause overheating issues or trigger limp mode, potentially damaging the transmission. A Chevy Silverado owner with 1.2 million miles on their Allison transmission on Reddit recommends regular fluid changes, filter swaps at 25,000 miles, transmission fluid flush at 100,000 miles, and a double-drain refill and internal filter swap at 200,000 miles. 

Adopting proper driving habits can also extend the lifespan of an Allison transmission. Aggressive shifting and wheel hopping place unnecessary strain on the transmission, leading to overheating and premature wear. If you are rebuilding your transmission, only use high-quality parts designed for heavy-duty applications. Lastly, if you are facing any of the above problems with an Allison transmission and your vehicle is eligible, you can take advantage of Allison's standard limited warranty as well.