An Inside Look At A Merchant Automotive Allison Upgrade For Towing - Diesel World

An Inside Look At A Merchant Automotive Allison Upgrade For Towing

Regular readers know how easy it is to make significant power with a modern diesel truck. By simply uploading a more aggressive engine tune and upgrading the intake and exhaust, a Duramax-equipped truck can safely reach 450-500 horsepower at the rear wheels. Yet, it doesn’t matter how much power one can coax out of an engine if it fails to effectively get the power to the ground. Case in point: a stock Allison transmission shifts smoothly and works well at stock power levels, but once engine performance is upgraded or placed under the rigors of exceptionally heavy (and regular) towing, the venerable Allison becomes the proverbial “weak link” in the chain.


To combat any Allison transmission weaknesses for Duramax owners, the experts at Merchant Automotive in Zeeland, Michigan, have developed the MA450 transmission specifically for those who want the reliability and dependability of trouble-free towing. Rather than call their transmissions by Stage A, B, C or some numerical equivalent, the team at Merchant Automotive uses a naming structure based on the recommended horsepower levels for each transmission. For instance, the MA450 is suggested for towing applications for trucks making up to 450 horsepower at the rear wheels. For those making competition level power, they offer the MA700. They also offer the MA1000 for the ultimate performance Allison transmission rated up to 1,000-horsepower using the same upgrades as the MA700, but with the addition of billet input and output shafts for additional power handling capability.

Though the MA700 and MA1000 are certainly capable transmissions, they remain a poor match for the daily driver and towing needs of most Duramax owners. This is where the MA450 comes in—it’s not as capable as its bigger brothers but it comes in at a price that’s not only budget friendly, but also offers substantial improvement over the factory Allison transmission. The MA450 is not recommended for owners who want to sled pull or race their trucks; for those customers the crew at Merchant suggests stepping up to the MA700 or MA1000.

1 When building an MA450 they use everything shown here including new clutches and steels, Torrington bearings, bushings, TransGo shift kit and a deep Allison pan along with the Goerend PTO covers.

2 Dennis Delo starts the rebuild by draining the transmission and removing the factory stamped steel torque converter before tearing down the transmission to the bare case.

3 You can see that excessive heat has started to damage the C-2 clutches and steel within the transmission. Yes, we’ve seen worse than this but obviously their holding power is reduced from slipping and heat buildup.

4 The C-3 clutch pack has also been slipping and shows signs of heat damage as well.

5 Delo rotates the transmission on the stand and removes the tail housing and output shaft as well as the clutch packs and planetary gear sets.

6 Even though this set of clutches did not appear damaged, the Merchant Automotive crew replaces them rather than reusing them so that the MA450 has new clutch material throughout the transmission in every clutch pack.

We’d love to be able to give you a complete step-by-step article covering the build of an Allison transmission by the techs at Merchant Automotive, but the fact of the matter is that we just don’t have the space in the magazine to cover all of the intricate details (we shot more than 1,000 photos while we were observing the rebuild). In this article, we’ll highlight the aspects of the MA450 that make it superior to a standard Allison rebuild. We visited their shop and followed along as veteran transmission builder Dennis Delo walked us through the process of building a MA450 for Matthew Alcumbrack’s 2005 Chevy Silverado 2500 HD, a vehicle he uses to tow his fifth-wheel RV trailer, family boat, and heavy work trailer.

When building an MA450, the crew at Merchant starts with a standard Allison core and tears it down to the bare case. Then they clean the case and internal hard parts in their hot tank parts washer to give the rebuild a fresh starting point. While reassembling the transmission, they use new Torrington bearings and select bushings as well as a complete set of new gaskets, seals and O-rings to ensure leak-free operation. The hydraulic system is also improved to provide more holding power for the internal clutches as well as the lock-up clutch within the torque converter for improved longevity over the stock hydraulic configuration. By installing a TransGo Allison Shift Kit, typical Allison shifting problems are eliminated while providing crisp yet smooth upshifts and downshifts. A complete set of new OEM clutches and steels are also installed, which work with improved hydraulics to handle more power than typically would a stock configuration.

An Allison deep sump pan is included to provide additional fluid capacity and better cooling capability. A deep filter and billet aluminum filter lock are used to make sure that the fluid stays clean and does not starve the transmission from the filter falling out of the inlet port. Of course, they also supply a new external Allison spin-on filter for the transmission. They also drill internal fluid passages to help lubricate the hard-working C-3 clutches and use the cast aluminum Goerend Allison PTO covers that
funnel fluid directly to the C-3 clutch pack for additional lubrication and cooling. The MA450 build also features a single-disc torque converter with a billet front cover to pass power from the engine to the transmission without slipping and loss, providing more holding power than the factory converter.

7 After rotating the transmission once again, Delo removes the valve body to give it a rebuild with the TransGo components to improve shift performance and control.

8 and 9 Once everything is removed from the main Allison case, Delo mounts the Goerend jig to drill fluid passages to provide additional lubrication and cooling to the C-3 clutch pack with the Goerend cast aluminum PTO covers. The hole is drilled at a precise angle to channel the fluid directly to the C-3 clutch pack.

10 Delo loads the hard parts into the shop’s hot tank washer to thoroughly clean all the components before they are reassembled.

11 When reassembling an Allison transmission the team at Merchant Automotive uses all new seals, gaskets and select bushings to bring the transmission back to a better than new state. Delo lubricates the O-ring seals before installing the components to prevent them from ripping or tearing and creating an internal fluid leak in the hydraulic system.

12 He also lubricates the new Torrington bearings as they are installed to prevent a dry condition on startup that could damage the new bearings before they really even get used.

13 Merchant uses a new Allison P1 drive flange (seen on left) since many of the original drive flanges are worn, especially in high-mileage transmissions. The drive flange wear typically happens at the internal splines that lock around the P1 sun gear inside the transmission.

After Delo completed the MA450 transmission assembly, the unit was handed off to Sam Derks to install it in Alcumbrack’s Silverado. After the installation, it was filled with fluid and taken on a test drive before being handed back to Alcumbrack, ready to tackle all of his towing needs. The team at Merchant recommends Allison TranSynd transmission fluid for their Allison transmission builds. If you want to upgrade to a Merchant Automotive MA450 in your Duramax truck you can remove your transmission and ship it to them to be rebuilt as an MA450 or purchase one from them with a core charge and install it yourself. If you do perform the removal and installation yourself, be sure to practice safe shop techniques, especially when working with your truck on a lift or jack stands.

Of course, you can also pick one up from the shop directly or have them install it for you if you’re local to Zeeland, Michigan. No matter how you go about getting an MA450 into your truck, it will be much better equipped for towing. Follow along over the next few pages to see an inside look at what makes the MA450 an
improvement over a stock Allison transmission. For more details on the MA450 or other Allison options from Merchant Automotive point your browser to or give them a call at 866-399-7169 and tell them your friends at Diesel World magazine sent you. DW

14 The drive flange and sun gear are loaded into the drum following the internal clutches that Delo already replaced with new OEM clutch packs.

15 and 16 Delo completely disassembles the valve body and hones the bores to make sure the new plungers do not hang in the bore and cause erratic operation.

17 Comparing the new plungers and springs (on the left side of the pairs) to the original does not show a huge difference but installing the kit to optimize the valve body helps the transmission to work better and handle more power without slipping.

18 Delo completes the valve body upgrade by properly torqueing all of the hardware before setting the valve body aside to be installed later.

19 and 20 19 and 20 After the transmission case is cleaned and given a fresh coat of paint, Delo installed one of the Goerend PTO covers to show us how the diverter cast into the cover directs the fluid toward the hole he drilled earlier (see arrow) to help lubricate and cool the C-3 clutch pack. The covers replace the factory covers simply bolting into place after the internal passage is drilled, be sure to install them on the correct sides of the transmission as indicated since they are directional.

21 Delo next installs and secures the drum, then rotates the transmission case to install the clutches in the rear section.

22, 23 and 24 He carefully installs and aligns the new clutches and steels as well as the apply pistons and planetary gear sets lubricating the new Torrington bearings along the way.

25 ­­­Once everything is buttoned up at the rear of the transmission, Delo installs the tail housing and torques the mounting bolts.

26 Then, after flipping the case one more time on the stand, he installs the rest of the clutch packs on the front side of the case.

28 He also installed the drum into the pump and tested those clutch circuits with air pressure.

29 Do not forget to clean and reuse the magnet that’s housed under the spin-on external filter whenever you change the filter. The team at Merchant Automotive installs a magnet if it’s missing from a previous owner throwing it out with their old filter.

27 After the clutches are installed in the case, Delo uses air pressure and a Sun Coast machined block to test each clutch apply circuit, making sure that the transmission will work properly when it’s installed in your truck.

30 Delo installed the valve body after turning the transmission in the stand once again.

31 Since they use an Allison deep transmission pan and filter on the MA450 transmission builds, the Merchant Automotive crew also use a Sun Coast machined retainer (see arrow) to hold the filter securely in place and prevent it from falling off and causing the pump to suck air and damage the transmission.

32 To better transfer engine power to the transmission, Merchant uses a new single disk torque converter with a billet front cover that’s much stronger than the factory stamped steel torque converter shown on the left.

33 To complete the assembly Delo installs and engages the new torque converter in the rebuilt transmission. If you’re ever installing a torque converter yourself make sure it’s fully seated and spins freely before trying to install the transmission in the truck. You could damage the pump if the torque converter is improperly installed.

34 Sam Derks uses a transmission jack to lift the MA450 up into Matthew Alcumbrack’s 2005 Chevy Silverado 2500 HD, then reconnects the harnesses and cooler lines and reinstalls the transfer case and drive shafts.

35 After finishing the installation, Derks fills the transmission with TranSynd fluid and road tests the truck to verify that everything is operating properly.

Merchant Automotive