Getting Up to Speed

Installing Duramaxtuner’s 6-SPD Conversion Kit in an LB7

It has officially been twenty years since GM introduced the Duramax and Allison transmission combination to the light duty truck market, and it’s safe to say it’s been a winner right from the start. That Duramax diesel engine has been a major success for the GM camp and has been a top contender in just about every aspect of this truck space. The motor has always generated competitive power and torque ratings with it’s Cummins or Power Stroke counterparts. Backed with the always solid Allison transmission, they just flat out worked whether it was heavy towing, daily driving, or weekend hot rodding.

The 6-spd conversion kit has been perfected by the team at and offers early Duramax owners that extra 14% reduction in RPM’s when cruising. For the LB7 and LLY, that additional gear can really make the difference in both power delivery and efficiency.
For some, the thought of changing out a valve body and making changes to the transmission controller may be a bit overwhelming, but this kit has been well thought out and includes the documentation to help settle some of those nerves on install.

The very first version of the Duramax, the LB7, used in 2001-2004 model years is still to this day revered as the best version of Duramax by many. It offered solid fuel mileage and great power potential with some modification. That’s not to say the LB7 doesn’t have its pitfalls (injector failures, head gaskets to name a few) but with the right combination of parts, that LB7 and 5-speed Allison makes for a great package. As the years went on, the Duramax had to adopt new technology to keep up with the times. GM had to quiet them down to please owners, they had produced more power in stock form to keep up with the competition, and of course they had to have cleaner emissions to satisfy the EPA. This meant new fuel injection systems, variable geometry turbos, and EGR coolers.

Of course, in order to swap out that valve body that is housed within the transmission, the pan fluid must be drained, and the pan dropped. So, what better time to complete a transmission service. New internal filter, new spin-on external filter, and a couple gallons of Allison’s TranSynd automatic transmission fluid.
This is a job that can be completed at home with a few jack stands under the truck and some time. You’ll just need enough room to slide under the truck to get access to the transmission pan bolts. Make sure you have a good catch pan. Even with the fluid drained from the pan, you’ll still have a bit of a mess on your hands as the valve body will still hold some fluid and continue to drip through the swap process.

Through all this development on the engine side of things, there were also some changes made within the Allison transmission to improve the overall drivability and efficiency of the GM trucks. In 2006, the 6-spd was introduced and it really helped set that LBZ apart from the competition. Not only did the 2006 Duramax have the power and clean emissions demanded in it’s day, that transmission could just do everything better than the competition. It always had the right gear for the situation, and with the newly added double overdrive, the LBZ got lower RPM’s at highway speeds for better mileage to boot.

This job can be done with basic hand tools, but the help of air tools will speed it up some. If you plan to reassemble with air tools, use extreme caution to not overtighten the pan bolts, as they are being threaded into the aluminum transmission case.
With the pan off, you’ll get your first glimpse at the current 5-spd valve body. While it may look pretty similar to the new 6-spd version from, once they are on the bench together, the differences will become obvious.

From there on out, well at least until this latest 2020 Duramax model came around, that 6-speed Allison has been GM’s major success story. For more than fourteen model years, the 6-speed Allison 1000 was being bolted up behind the ever changing Duramax. Why you ask? It just flat works, that’s why. Sure, there were some minor changes made within the transmission through the years to make sure it was up to the task as GM continued to increase engine outputs and make engine variations from the LBZ, LMM, LML, and lastly the L5P but for the most part, that 6-speed Allison just kept trucking along. I just kept doing what it did best, transferring big power and torque, efficiently, to the tires.

Using a socket and short extension, you’ll be able to push the valve bodies main wiring harness connector back into the transmission case. That main wiring harness has a large seal all the way around it where it comes through the case, this little trick makes removal a cinch.
With the original 5-spd valve body (right) and the new 6-spd valve body (left) sitting side by side you can see the difference by looking at the electronic solenoids on the back. Notice the additional solenoid in the lower right corner?

In the aftermarket space, of Woodstock, IL has had their hands in the Duramax and Allison market for over a decade. It’s fair to say they’ve seen everything, tried everything, and excelled at everything as far as the Duramax platform is concerned. Whether they are doing custom tuning for an otherwise stock truck looking for a little extra mileage or building all-out competition drag race or sled pull trucks, they have as much experience and knowledge of the Duramax engine and Allison transmission as anyone in the industry. Looking to capitalize on the benefits that 6-speed Allison brought to the table in 2006, the team set out to offer a complete conversion kit to offer to the 2001-2005 Duramax owners looking to get the most from their factory 5-speed applications.

Here you can see the lower portion of the transmission with no valve body installed. This transmission has previously been upgraded from stock with additional clutches, triple disc torque converter, and we’re replacing a modified valve body that had been improved to handle the 550-rear wheel horsepower this particular truck produces.
Installing the new 6-spd valve body is no different than if we were bolting the original unit back in place. You’ll also need to get that large wiring harness connector pushed out through the case and properly sealed.

Their 6-speed conversion kit was developed to bring that additional gear to the LB7 and early LLY model trucks to help eliminate some of the wear and tear on your engine cruising at higher speeds. The added gear also means more efficient usage of your power curves, keeping the motor in its peak efficiency range for more of your daily driving situations. Because team has the experience in tuning both engines and transmissions, the package also includes the required Transmission Control Module (TCM) to offer the absolute best shifting strategies possible with the new gearing. While you may have your current setup dialed in to your liking, and simply adding an additional overdrive into the mix sounds simple enough, remember power management and shift strategy can make or break your driving experience and this is where the 6-spd conversion really shines.

The valve body torque sequence is vital to a leak free seal and proper transmission function. There are quite a few bolts that hold the unit in place and a very particular torque sequence must be followed to make sure it seals to the case properly and no fluid leaks from one passageway to another when it isn’t supposed to. A properly calibrated torque wrench will be the only real specialized tool you’ll need for the swap.

The teams understanding of TCM control really raises the bar and will have you falling in love with your old truck all over again. For towing, the TCM works to keep you in the gear you need when that low end torque can really do the grunt of your heavy towing tasks, while the perfectly times downshift, can extend the RPM’s and increase boost levels to maintain safe EGT’s over a long grade. Obviously, the main reason for making a swap to the 6-speed is for fuel economy. Lower RPM’s has to mean better fuel mileage, right? Well, in most cases, yes. Making this swap should equate to better highway mileage as your logging a lot of miles on your truck commuting to and from work or hauling trailers across the country. Making the switch from 5-speeds to six should offer about a 14% reduction in engine RPM’s while cruising. So, a 2250rpm at 80mph easily drops to 1950, where that engine will sing much happier and efficiently.

One final thing to be sure you’ve paid attention to during the installation is that the gear shift lever has engaged within the shift linkage of the valve body. If this step gets missed, you’ll soon find that the shift lever on your steering column does nothing and you’ll be draining fluid, dropping a pan again before you’ll get to try that new double overdrive out.

The addition of a 6th gear for LB7 owners also has an added benefit you might not even consider at first. Noise reduction. The LB7 is obviously the loudest Duramax platform, with the older injector technology, the injection system just generates more noise in the cab, and that new double overdrive means less RPM and less cab noise while running down the highway. As a true ‘package’ the engineering team behind this kit really thought through the process, how you’d be using your truck, what you’d expect to gain, and how to make the best driving experience for you as possible. The 6-speed conversion kit will still work with aftermarket tapshifter kits, so you can continue to manually control your shift patterns when you’d like, and it will even work in conjunction with the popular Edge Insight monitors to display your true gear, since your factory dash won’t read past fifth gear.


‑For our test truck, a super clean and moderately modified 2004 LB7, the 6-spd conversion was the last remaining piece to building the ultimate LB7 daily driver. This truck runs a stout built transmission, head studs, 64mm S300 turbocharger, and fuel system upgrades to produce anywhere between 450-550hp depending on the tune choice for the day. It’s only brought out of the garage on sunny days and will spend its weekends tied to a trailer at the boat ramp. When it’s driven, it’s driven hard, and more often than not it’s towing on long weekend trips around the state of Utah. The 6-speed conversion turned out to be the absolute best final step to this build. The drop in RPM’s makes highway towing more pleasurable in every way from the increased fuel economy to the decibel drop in the cab from the engine purring along at a lower RPM range. The TCM shift strategy that was built for this truck’s parts combination, gear ratio, and tire size has been spot on and there have only been a few instances where we’ve found the manual shift mode really even needed. This combination just works, it shifts when it should, finds the RPM’s it needs to make the power being asked for, and hasn’t done anything strange to make you think it’s confused to do what you ask it to with your throttle input.

Fully reassembled with a brand new internal fluid filter installed, this truck is ready for a transmission pan and some fluid. It is also recommended to change your external filter at this point as well. The final step to this 6-spd conversion is swapping out the trucks TCM for the new unit supplied by You’ll find that mounted up on the driver side of the fan shroud.



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