Project Work Truck: Simple Transmission Upgrades For Towing And Hauling

Simple Transmission Upgrades For Towing And Hauling

When operating behind a factory 7.3L Power Stroke engine making around 250 horsepower, the 4R100 is a great transmission and will generally perform well for many years and many miles even when towing heavy loads. But when performance modifications ramp up the horsepower and torque, most stock transmissions reach their limits, including the 4R100. Rather than wait for problems to develop, it’s better to be proactive and upgrade the transmission before really turning up the wick on your Power Stroke’s performance.


That’s the route that concrete contractor Vincent Uriah of Summerville, Georgia, decided to take with his 125,000-mile 2003 Ford F-350. He turned to the experts at Swamp’s Diesel Performance in LaVergne, Tennessee, to install one of their performance modified valve bodies, modified TransGo valve body plate, Precision Industries torque converter and Mag-Hytec transmission pan to hold an additional 7.6 quarts of Schaeffer’s ALL-TRANS Supreme fully synthetic transmission fluid.

Rather than a full transmission build, the crew at Swamp’s will simply be upgrading the transmission since it has relatively low miles, still shifts firmly, and the fluid did not show any signs of abuse or excessive wear. If the transmission is already slipping and has worn or damaged clutches it needs a full rebuild, not just an upgrade.

In a transmission like the 4R100, the valve body is the brain of the transmission and controls its operation, including line pressures, gear selection and shift firmness. By modifying the valve body and installing the modified TransGo valve body plate, the team at Swamp’s is able to not only extend the life of the transmission, but also allow it to handle the additional power that Uriah’s F-350 is now making as well as more power to come in the future.

With overdrive transmissions and lock-up torque converters in automatic transmissions for diesel applications, the torque converter has an incredible load put on it, especially with modified engines. The factory converters are usually okay for stock power levels, but will not hold up well to additional power. Their weak single-clutch assemblies and stamped steel construction are just not strong enough to handle high-torque loads especially when heavy towing is involved. The option for this truck is a Precision Industries heavy-duty torque converter that can handle the power and towing demands.

The Stallion torque converter from Precision features a one-piece machined billet cover for added strength and rigidity to make a strong foundation for the converter. The internals consist of a multi-disc clutch that has more than 3.5-times the surface area of the factory clutch for solid engagement that will not slip even under heavy loads with high-power engines. The new converter also includes a five-year warranty and will generally provide fuel mileage improvements due to better fluid coupling as well as better acceleration thanks to increased torque multiplication.


1 Swamp’s Diesel Performance technician Dan Morin starts the installation by removing the driveshaft.


2 Then he removes the torque converter inspection/access cover and removes all six of the original torque converter mounting nuts.

Installing the modified valve body and valve body plate can be done with the transmission in the truck as can swapping out the pan, but to replace the torque converter the transmission must be removed from the truck. We followed along as Dan Morin performed the installation on Uriah’s F-350 at the Swamp’s shop. Fortunately for us, he used one of the shop’s drive-on four-post lifts so we were easily able to be under the truck with him to capture the following photos and bring the highlights of the installation to you.

Morin had the transmission out of the truck in well under an hour, then he cleaned up the case, swapped out the converter and reinstalled it back in the truck. Before he reinstalled the transmission, he poured out the used fluid from the old torque converter directly onto his transmission bench to analyze the fluid. There was very little metal found suspended in the fluid and it did not smell burnt, verifying his prediction that the 125,000-mile transmission has been well maintained and is in reasonable health.

Once the transmission was back in the truck he drained the rest of the old fluid and removed the pan and filter. Then he removed the old valve body and replaced it with a valve body that he rebuilt and modified earlier in the day, sandwiching the modified TransGo plate between the transmission and the valve body.


3 After properly supporting the transmission with a transmission jack, Morin removes the rear crossmember.


4 The transmission harness and linkage also need to be removed and the cooler lines need to be disconnected before the transmission can be pulled from the truck.


5 Morin uses an extra-long extension and a cordless impact gun to access and remove the bell housing bolts securing the transmission to the engine.


6 Once everything is free the transmission can be slid back away from the engine and lowered down out of the chassis.


7 Make sure you have a bucket or drain pan handy before removing the original torque converter from the transmission or you’ll have a big mess all over the floor with several quarts of used transmission fluid.



8 & 9 The differences between the Precision Industries Stallion converter and the factory converter are as obvious as Precision’s trademark pink paint. The Stallion uses billet steel parts that are much stronger than the factory stamped steel and internally has better clutches with much more surface area for more holding power.


10 Morin pours enough Schaeffer’s ALL-TRANS Supreme fluid (about a quart) into the vertically stood-up converter to fill the bottom half of the converter without spilling a bunch of fluid on the floor.


11 After sliding the torque converter onto the transmission input shaft, Morin carefully rotates it, making sure that it fully engages the pump and spins freely with no binding.


12 After raising the transmission into position, Morin once again relies on a long extension to make accessing the bell housing bolts much easier.


13 He uses medium-strength thread locking compound on the mounting bolts provided with the torque converter before installing them to secure the new converter to the flexplate and make sure that it does not come loose.

After the valve body, he installed the new filter that was supplied by Mag-Hytec. When removing the old filter and installing the new one, be sure that the old seal comes out and if it’s stuck, remove it very carefully so that you do not damage the bore and create an internal leak in the transmission that would hurt performance and potentially damage the transmission. Before installing the pan, Morin chased the threads in the transmission case to clear any road grime that had built up in the upper portion of the threaded mounting holes.

Once the pan is buttoned up and the truck is lowered back down to ground level, he filled the transmission with 16 quarts of Schaeffer’s ALL-TRANS Supreme fluid before starting the truck and topping it off. The total transmission capacity will be close to 24 quarts (or six gallons) of fluid with the deep pan so be sure to have enough fluid on hand to complete the installation. A word of caution in filling the transmission, though, do not fill all of the fluid before starting the truck as it will overflow and leave you with a big mess on the floor.

Advanced DIY diesel enthusiasts can handle an upgrade like this themselves in their garage or driveway. Unfortunately, working with the truck (properly supported) on jack stands will be more difficult than using a lift in a professional shop, but it’s doable, it will just take more time and effort. You may need a friend to bar over the engine so that you can access all the torque converter bolts to unbolt it from the flexplate before removing the transmission and again to install the new bolts securing the Precision converter to the flexplate.


14 You will have to bar over the engine to reach all six of the mounting bolts like when removing the factory torque converter nuts.


15 With the transmission reinstalled and reconnected, Morin drained the fluid and removed the pan to access the valve body.


16 Eleven 8mm bolts and two 10mm nuts secure the valve body. Be careful when removing it, as more fluid will pour out of the transmission internals above the valve body.


17 Morin disassembles and modifies each valve body that goes into a Swamp’s transmission to optimize the shifting and internal pressures for great performance and power handling capability.


18 Here’s an exploded view of the valve body. If you attempt to modify or rebuild the valve body yourself rather than purchasing a modified one from Swamp’s beware that all of those springs and pistons are critical to the performance of the transmission and if they’re lost or incorrectly assembled it will not perform properly. Sometimes it’s better to leave things to the experts.

With the Swamp’s modified valve body installed in the transmission, the shifts are crisper but not overly harsh and the torque converter lockup is solid. We expect fuel mileage to be slightly improved, but the main reason for the upgrade was to strengthen the 4R100 transmission to hold up to increased power, especially when towing heavy loads. In last month’s issue, the crew at Swamp’s gave the truck more power with intake, exhaust and tuning upgrades and they’re planning to give it even more power in the future. Stay tuned and follow along with the monthly upgrades on the old work truck. DW


19 Morin also modifies the cast aluminum valve body case before reassembly.


20 He uses new springs and pistons when assembling the valve body to optimize the performance to the customer’s specific needs. Steel pistons are used to prevent sticking that’s possible with the factory aluminum pistons riding in the aluminum bores.


21 Before installing the modified valve body, remove the press-in filter screen from the gasket and install the modified TransGo valve body plate, then press the filter back into the hole (see arrow).


22 The filter will hold the plate in position while you slide the valve body onto the studs sandwiching the TransGo plate between the transmission and the valve body.


23 Tighten the mounting bolts to 80-100 inch-lb working from the center of the valve body outward to secure it to the transmission.


24 The deep pan for the 4R100 from Mag-Hytec is made from cast aluminum and holds an additional 7.6 quarts of transmission fluid and features internal and external fins to help the transmission run cooler. They supply everything needed to install the pan, including mounting bolts and washers, Allen wrenches and a new filter.


25 After installing the new filter, the new Mag-Hytec pan can be installed and the mounting bolts tightened to 12-16 ft-lb, Morin lubricates the pan’s integrated O-ring seal with a little transmission fluid to get a good seal against the transmission case. Be sure to follow the installation instructions regarding the placement of the shorter mounting bolts to avoid damaging the transmission case.


26 The finished transmission not only looks better to anyone who happens to peek under the truck, it will also run cooler and shift better.


27 To wrap up the upgrade, Morin fills the transmission with Schaeffer’s full synthetic transmission fluid, first with 16 quarts, then topping it off after starting the truck.

Dept. DW
14718 Arminta St.
Van Nuys, CA 91402

Precision Industries
Dept. DW
120 Independence Dr.
Whiteville, TN 38075

Schaeffer’s Specialized
Dept. DW
102 Barton St.
St. Louis, MO 63104

Swamp’s Diesel Performance
Dept. DW
304 Sandhill Road
LaVergne, TN 37086

Dept. DW
2621 Merced Ave.
El Monte, CA 91733