When it comes to GM’s heavy-duty light trucks over the last 20 years, two things have remained constant, the 6.6L Duramax and the Allison transmission. While they have been refined over the years, there is no denying this combo has proven itself to be one of the best light truck drivetrains on the market. Simply put, they are reliable workhorses that get the job done day in and day out.

Even though the Allison 1000 has proven itself to be a capable transmission and will last a few hundred thousand miles when properly maintained, high horsepower and frequent heavy towing will take their toll over time. At Merchant Automotive, we have seen this time and time again, which led us to create our Merchant Maximum Transmissions for severe work and track use and suffice to say, it will be the last transmission you will need for your truck.

Why Does General Motors Use Allison Transmissions?

Allison Transmission is the world’s largest manufacturer of medium and heavy-duty transmissions, and they didn’t reach that level by making a sub-par product. Simply put, they are known for their engineering and have an established reputation for producing durable transmissions. It should be noted that when the Duramax debuted in 2001, GM wanted a transmission just as tough as the engine, so they turned to the world leader in heavy duty transmissions, Allison. 

Suffice it to say, the Allison 1000 was a leap forward over anything Dodge and Ford had to offer, and it became the envy of the competition. Like the Duramax, it featured a lot of new techs for the time and was without a doubt the most intelligent transmission when it debuted. Likewise, the first versions used behind the LB7 and LLY had five gears (6 for the LBZ and later) for better fuel economy.

Other features were an advanced transmission control module (TCM) that optimized the shift points and improved fuel economy. Simply put, it was strong, durable, and relatively maintenance-free aside from changing the fluid. When properly maintained and not abused, the Allison 1000 will, in many cases, last for the life of the truck.

As the Duramax has evolved, most notably with the LBZ and LML, the Allison received appropriate upgrades to handle the extra power. However, as a credit to its design, it has remained relatively unchanged, even as the new emissions standards took effect in the mid-2000s. In fact, the most significant revision occurred in 2020 when a 10-speed version debuted.

As with most things in the auto industry, fuel economy standards and tighter emissions laws have been behind many recent changes. However, the Allison 1000 is not bad in any way, and it took the competition years to catch up. With that said, the Duramax and Allison transmission are probably the best drivetrain combo that you can find on any light truck today.

Why Do You Need a Transmission Upgrade?

There is no doubt that the Allison 1000 is an excellent transmission, and it can handle some extra power without an issue. However, we all know the Duramax responds well to modifications, and stock is not enough for many owners. While the Allison was revised several times, most notably after the power increases to the LBZ and LML, aggressive tunes and bigger turbos are more than the stock unit was designed to handle.

It should be noted the same holds true for any diesel truck regardless of the make, aggressive tunes and bigger turbos will drastically reduce the transmission’s life. This is especially true if you have a higher mileage truck, you will find yourself needing a Merchant Maximum Transmission sooner than later.

Now you are probably wondering what the breaking point of the Allison 1000 is. As it has been upgraded over the years, we have broken it down by model below:

• 2001-2005 LB7/LLY: The 5-speed version was the weakest of the lot, and generally speaking, 350-400 rear wheel horsepower (RWHP) or about 100 over stock is usually the limit in terms of reliability. Generally speaking, this is anything beyond a moderate tune and some supporting modifications like a free-flowing exhaust and a cold air intake.
• 2006-2010 LBZ/LMM: Aside from having a sixth gear that improved fuel economy, the Allison received upgraded internals that mirrored the LBZ’s extra power. It did not really become a liability until around the 450 (RWHP) mark.
• 2011-2016 LML: As the LML received a sizable boost in horsepower and torque, the Allison was strengthened to match it. It also featured a more advanced TCM and was generally able to handle 500 (RWHP) without much issue.

In the end, it comes down to how you drive your truck and how well it is maintained. Likewise, a transmission with 100,000 or 200,000 miles on it will not handle the extra power like a new one. Adding an extra 100 horsepower will put additional stress on the transmission and wear the internal components like the clutch packs or torque converter even faster.

Suffice to say, the transmission will be on borrowed time, so if you plan on modifying your Duramax, one of the first upgrades should be a Merchant Maximum Transmission.

Why Merchant Automotive's Maximum Transmissions Are the Best Rebuilt Allison Transmissions You Can Buy

When you drive a heavy-duty truck, you know the transmission is the powerhouse that keeps everything running smoothly. But when it comes to Allison transmissions, only the best will do. That’s where Merchant Automotive steps in. Our Maximum Transmissions are rebuilt from the ground up, ensuring every single component is inspected and perfected for ultimate performance and long-lasting durability.

What Makes Merchant Automotive Maximum Transmissions Stand Out?

At Merchant Automotive, we’re not just rebuilding transmissions – we’re crafting precision machines that give your truck the reliability and power it needs. Every Allison transmission we work on is completely disassembled, inspected, and rebuilt with top-tier components. From the smallest springs to the largest gears, we ensure everything is in peak condition before sending it back to you.

And here’s what really sets us apart: We test everything we build. Our transmissions are built to last, and we ensure that each one meets our customers’ high standards. You can count on your transmission to provide the same performance and durability you expect – mile after mile.

With over 20 years of experience, we’ve been building Allisons for customers all across North America. Our customers keep coming back because they know our commitment to quality and performance never wavers.

Two Series, Built for Your Needs

We understand that different drivers have different demands. That’s why we offer two series of Allison transmissions – each designed for specific levels of power and performance.

1. Work Series: This is perfect for truck owners who need to replace a failed stock unit but don’t want to lose the factory feel of their truck. The Work Series is designed for those who use their trucks for towing and might have up to 150 horsepower more than stock. It provides the stock driving experience you’re used to, but with increased durability to handle the extra power and heavy loads. This series is for drivers who need a reliable upgrade without sacrificing comfort or everyday drivability.
2. Pro Series: For those who have taken their truck’s performance to the next level by upgrading the turbocharger or making other high-performance mods, the Pro Series is for you. Designed for trucks with over 150 additional horsepower, this series is built to handle the extra power with increased holding capacity, making it ideal for high-performance use. It comes equipped with billet stator torque converters for maximum durability and can include optional upgrades such as billet shafts and heavy-duty hubs, giving you the ultimate in reliability and strength.

Fully Tested Valve Bodies for Maximum Performance

One of the most critical parts of any transmission is the valve body. At Merchant Automotive, we go the extra mile by testing every valve body on our Superflow Axiline valve body test stand. This advanced testing equipment simulates real-world conditions, ensuring your valve body performs at its best. By catching potential issues before they reach your truck, we ensure maximum reliability and smooth shifting for the long haul.

Torque Converters: Matched to Your Needs

We don’t stop at the transmission. To make sure your truck is fully optimized, we also provide high-quality torque converters that are tailored to your specific needs. Whether you're hauling heavy loads or pushing for performance, we’ll match the perfect torque converter to your driving demands.

Our billet stator multi-plate torque converters offer increased durability, smoother engagement, and better heat dissipation, ensuring a seamless connection between your transmission and engine for years to come.

Our Process: From Rebuild to Road-Ready

1. Complete Disassembly: We take apart every piece of the transmission, inspecting it all for wear and damage.
2. Premium Parts Replacement: We use only the best aftermarket or OEM parts to replace anything that could impact performance.
3. Performance Upgrades: Whenever possible, we upgrade the transmission to ensure it’s stronger and more durable than the original.
4. Valve Body Testing: Each valve body is tested on our Superflow Axiline test stand, ensuring it's up to the task.
5. Torque Converter: We offer high-quality torque converters to match your specific driving needs.

Why Go With an Allison Transmission?

Allison transmissions are built tough for heavy-duty applications. But even the best transmissions need expert care to keep them running at their best. When your Allison needs a rebuild, you need a team that knows them inside and out – and that’s Merchant Automotive. With over 20 years of experience and happy customers all across North America, we ensure every transmission meets our exacting standards for durability, performance, and reliability.

The Merchant Automotive Difference

At Merchant Automotive, we’ve spent over two decades perfecting the art of rebuilding Allison transmissions. We take pride in our work and test everything we build to ensure it meets our high standards. That’s why our customers trust us to provide a transmission that delivers not only power but also peace of mind.

Ready to Upgrade?

If you’re looking for the ultimate in transmission rebuilds, don’t settle for anything less than the best. Choose Merchant Automotive Maximum Transmissions and experience the difference for yourself. Because when it comes to your truck, every mile counts.