After years of abuse, the 4R100 automatic transmission behind our 7.3L melted down in our '02 Super Duty F-250 that rides on 46-inch tires. Sometime during the past two years, a valve designed to warm the transmission during cold weather by bypassing the transmission cooler became stuck. This resulted in a gearbox that refused to send fluid to the radiator for cooling, even when the truck was pulling a heavy trailer loaded with another 2-ton 4x4.
 Our '02 Ford F-250 Super Duty...  Our '02 Ford F-250 Super Duty is a transmission torture chamber. The 7.3L Power Stroke output has been greatly increased with a bigger turbo, programming, and propane injection. In addition to the increased torque, the truck has gained about 1 ton of extra weight (it weighs 8,450 pounds empty), and the 4R100 is responsible for turning giant 46-inch off-road tires. The stock 7.3L transmission cooler uses just nine passages for cooling, while the 6.0L part uses 25 rows. Luckily for us (and anyone else with a 7.3L), both parts use the same mounting locations. |  After putting the Super Duty...  After putting the Super Duty in the air, the South Bay Truck & 4x4 crew started disconnecting the transmission by unplugging all the electronics and removing the coolant lines. Even if you don't put your truck on a lift, you'll need a jack to remove the transmission without damaging it and to avoid serious personal injury caused by a falling gearbox. The installers at South Bay Truck & 4x4 use a jack with custom brackets to hold the transmission snugly along with a wood block to protect the transmission case and pan from getting bent or crushed. |  We'd be keeping the high-capacity,...  We'd be keeping the high-capacity, finned, aluminum PML pan upgrade, so it was removed from the broken transmission. It had to be washed with brake cleaner to remove the burned remains of the old 4R100 before it was installed on the new transmission. The BTS 4R100 we received included a full billet steel torque converter (painted purple, left) designed to lock up much firmer than the stock unit. The specifics about the transmission internals are a BTS secret, but they include custom planetary gears and stronger clutch packs along with a few other classified tricks. |
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You can probably guess what happened next-the transmission failed one day during the commute to work. First it lost Overdrive, then it began acting skittish before it eventually went into limp-home mode, which kept speeds under 30 mph. Driving that slowly on the freeway is not the best way to make friends in Los Angeles, so we contacted Brian Thompson of Brian's Truck Shop in Lead Hill, Arkansas, and ordered one of his custom-built 4R100 transmissions along with an auxiliary fluid cooler (PN 5C32-7A095-CB) designed for 6.0L Power Stroke trucks. The transmission cooler fits the stock 7.3L location, but as you can see in the comparison photos (above), it more than doubles the stock surface area for cooling transmission fluid.
When our new-and-improved parts arrived, we piled them into the F-250 and made a slow trek down to South Bay Truck & 4x4 in Hawthorne, California. Our battered F-250 is no stranger to the crew at this performance shop because they installed the automatic that became toast after a factory part failed on the highway. Follow along as the tough BTS 4R100 is installed, then learn how to upgrade your transmission cooling system by more than 100 percent in just a few steps.