2001 Ford Mustang Bullitt Transmission Swap - 50-Caliber Automatic - Tech

The valvebody and separator plate come from the '03-'04 Mach 1 Mustangs, as BC Automotive's Darrin Burch notes these have the best of Ford's valvebody mods. He then modifies them to his own specifications.

Burch swaps out the split output shaft sealing rings for this one-piece design, as he believes the factory split units fail to provide adequate lubrication to the direct clutch assembly.

This is the reverse clutch pack with a four plate for a possible transbrake option later on. Burch employs a spiral lock ring to replace the factory snap ring (pictured). "The most common transmission failures I've seen in these are caused by the stock snap ring flying off at high rpm," he says.

Four key components to BC Automotive's 4R70W include the upgraded band, the 4R75W pump, the stainless steel forward sun shell and gear, and the intermediate stub shaft.

The carbon band on the left is used instead of the stock piece as its material holds better under increased heat.

The automatic overdrive intermediate stub shaft has undergone some changes over the years. At far left is the '93-'95 shaft with its deep groove at the base of the splines. This design, along with the two subsequent versions to its right, have all resulted in breakage at some point. The far right shaft is a custom 300M aftermarket piece that Burch uses.

BC Automotive provides solid lubrication to the tailshaft bearing via braided-line feeding from the line port on the case-a necessity for cars with 3.73 or lower gear because the driveshaft spins excessively fast and galling can occur. Burch also made note that only transmission cases with part numbers starting with F7A should be used. These are found in most all '97-and-newer vehicles and feature a beefier case with better lubrication.

Our test subject had been previously fitted with BBK long-tube headers, and the general consensus was that they would not work with the automatic gearbox. With 600 rwhp on tap, we weren't going to step down to a set of manifolds, so we called up Kooks Custom Headers in Bayshore, New York. Kooks hooked us up with a set of its stainless 1.75-inch long-tube headers, along with a 3-inch X midpipe to fit up to our existing DynoMax after-cat system. Our Bullitt owner had them ceramic-coated prior to installation.

The Kooks headers fit well around the 4R70W transmission, but we noticed there were some close encounters with the UPR K-member that was in the car. Notice the slip fit collectors.