Project Work Truck, Part 5: Rebuilding the 4R100 Transmissio

Project Work Truck, Part 5: Rebuilding the 4R100 Transmission for Towing and Hauling

If you’ve been following the build series of articles on the 2003 Ford F-350 7.3L Power Stroke work truck project (Running from June 2014 to the present issue of Diesel World—Ed.) you’ll likely remember that in Part 2 (July 2014) the crew at Swamp’s Diesel Performance performed an upgrade on Vincent Uriah’s 4R100 transmission aimed at providing more power handling and longevity with the high-mileage transmission in hopes that its service life could be extended. Swamp’s transmission specialist Dan Morin installed a new triple-disc torque converter as well as a deep Mag-Hytec pan and modified the valve body to increase line pressure and improve power handling.

Unfortunately for Uriah, the heavy towing of earth-moving equipment for his concrete business, combined with the additional power the 7.3L Power Stroke engine is now making, did not bode well for the factory clutches and the transmission started to slip under load. Upon teardown, Morin determined that the forward clutch pack suffered a catastrophic failure with the clutches completely self-destructing. The design and operation of the 4R100 transmission applies the clutch packs in a cumulative arrangement, meaning that the clutch packs apply and add to the previous stage to make the transmission shift gears. So once the forward clutch pack (which is engaged in all forward gears) started to slip, the clutches simply burnt themselves up, leaving the truck stranded.

Rather than rebuild the transmission to factory specs at the dealer or a local transmission shop, Uriah chose to trust the expert diesel specialists at Swamp’s Diesel Performance in LaVergne, Tennessee, once again. They suggested upgrading the 4R100 with an Xtreme rebuild kit from Sun Coast Converters as well as their four-disc coast clutch drum and 2-3 shift valve. In addition to using higher quality Raybestos clutches and Kolene-coated steels that handle high heat better, the Sun Coast kit features machined components to allow more clutches and steels to be used in each pack for more holding power and less heat buildup. The Xtreme rebuild kit and upgrade parts will work well with the valve body modifications Morin performed previously, allowing the transmission to work well with heavy loads and engines in the 450-550 horsepower range.

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Thanks to a Sun Coast Xtreme rebuild kit, billet torque converter and the guys at Swamp’s Diesel Performance, Uriah’s 4R100 transmission is ready to tackle any load.

1. Stripping down your automatic transmission and bringing the inside out is not something the best weekend wrench can handle. The task is best left to experts who have the tools and know the tricks to build your trans right. With a team like the one at Swamp’s, you can get your truck back on the road in no time, and enjoy years of worry-free service.

2. This set of clutches is the low/reverse set with the new Raybestos blue clutch discs on the left and the original clutches on the right. Both sets use the same number of discs in this clutch pack, but the blue set is an upgrade over stock.

3/4. Seen here are the direct clutches with the new Raybestos discs on the left. Notice that there are six clutches in the Sun Coast set compared to five in stock trim. This is possible because of the new thinner machined apply plate (left), seen compared to the stock unit (right).

Not only does the Sun Coast Xtreme rebuild kit use better quality clutches and steels in each clutch pack, it also uses additional clutches in the direct, forward, intermediate, coast and overdrive clutch packs to increase the holding power of the transmission. To fit more clutches, Sun Coast supplies machined apply plates in the direct, forward and overdrive clutch packs. In the intermediate clutch pack, additional room for more clutches is accomplished by Sun Coast including thinner steels with the rebuild kit. To fit more clutches into the coast clutch drum, Sun Coast machined a new retaining groove into the drum that allows the number of clutches to be doubled from two to four. As you would guess, there’s a purpose to squeezing additional clutch discs into the transmission—it provides additional power holding capability by spreading the load across more surface area.

After towing the Ford F-350 up to the Swamp’s shop, Uriah left it there for a three-day turnaround that included part of a day to pull, disassemble and clean the transmission case, a day to rebuild the transmission with the Sun Coast parts, and part of the third day to reinstall and road test the truck and optimize the tuning for the new transmission capabilities. Of course, our camera slowed down the process, and the guys at Swamp’s could have had the truck done in two days without our interference for photography during the assembly. To help facilitate the quick turnaround and get Uriah’s work truck back on the road and making money quickly, the builders opted to use a Sun Coast billet multi-disc torque converter rather than sending out the converter that was installed earlier to be serviced to remove the contamination from the transmission’s destroyed forward clutch pack.

Morin inspected the factory transmission internals and found that the damage was concentrated in the forward clutch pack that was severely slipping. The clutch material was completely worn off the discs in the forward clutch pack, leaving that section of the transmission with metal-to-metal discs that would not propel the truck at all. The heat buildup from the slipping clutches also damaged the piston spring and seal, which were also replaced. The overdrive clutch pack also showed signs of overheating and burning, but not to the extent of the forward clutch pack. Fortunately for Uriah, there was no damage to the case or other major internal transmission components like the planetary gear sets.

5. Trans tech Morin stacks the clutches and steels in the drum. This is done with each of the clutch packs alternating between steels and clutch discs.

6. As you can easily see, the clutch material has completely worn off the factory forward clutch set on the right. To handle more power, the Sun Coast kit uses five Raybestos GPZ clutch discs while the factory used four. Not only did the slipping clutches fail, the heat also damaged the spring and the piston seal.

7. Morin installed the clutches and steels into the forward drum, aligning the discs and installing the machined apply piston that’s included with the Sun Coast kit.

For a skilled transmission builder like Morin, this build was fairly typical with burnt clutches in desperate need of replacement and an owner in desperate need of getting his truck back on the road. He flew through the installation of the new components with meticulous skill and knowledge of exact placement, alignment and operation. We followed along with the assembly of the Sun Coast Xtreme rebuild kit, but due to space limitations we can only show you highlights. If you choose to remove the transmission yourself be sure to practice safe shop techniques. If you’re among the few who are bold enough to tackle the rebuild yourself, be sure to follow a service manual closely and work carefully through the rebuild process.

While we’re sure that most diesel enthusiasts won’t run out and try to rebuild an automatic transmission on their own, we wanted to bring this article to you to show you what makes a kit like the Xtreme Rebuild Kit from Sun Coast assembled by a skilled diesel technician better than a standard factory-style rebuild from your dealer or local transmission shop. Even if you decide to remove and reinstall the transmission yourself to save some money you can still have a diesel performance shop like Swamp’s Diesel Performance build the transmission for you to make sure your own 7.3L Power Stroke work truck can tow and haul whatever you need. Just be sure to tell them that your friends at Diesel World referred you. DW