Speedmaster Automatic Transmission Case

Speedmaster Automatic Transmission Cases: Built for Maximum Strength

When a high-horsepower build demands a transmission case that can keep up, Speedmaster delivers with a focused lineup of aluminum automatic transmission cases engineered to outlast and outperform their OEM counterparts. Whether you're building a bracket racer, a street/strip machine, or a dedicated drag car, Speedmaster's transmission cases are designed to eliminate the weak points inherent in factory castings — and then some.

SFI 4.1-Certified Safety and Performance

Every Speedmaster automatic transmission case carries SFI 4.1 certification, the industry standard for transmission safety in motorsport applications. This isn't just a sticker on the box — it reflects a genuine commitment to structural integrity under race conditions. These SFI 4.1-approved cases come complete with an adjustable transbrake release, a built-in flexplate shield, and a transmission shield to improve your vehicle's performance.

Powerglide, TH400, and Ford C4 Coverage

Speedmaster's automatic transmission case lineup targets three of the most popular performance transmission platforms in American motorsport:

• GM Powerglide (PCE628.1001): Speedmaster Powerglide transmission cases were developed to eliminate all weak points found in the original Powerglide case, resulting in one of the strongest cases on the market. Manufactured by mold process from heavy-duty aluminum, the cases are stronger and more ductile than OEM castings. The case features a roller bearing and is compatible with standard aftermarket Powerglide bellhousings.
• GM TH400 Turbo 400 (PCE628.1002): Speedmaster TH400 aluminum heavy-duty transmission cases are designed for ultimate strength by eliminating weak points and adding superior strength in every aspect of the stock Turbo 400. They are built with full-surrounding internal case "lugs" that retain the center support and pressure plate, and their tolerance for abuse has been improved to handle high-horsepower. The Turbo Hydra 400 cases are manufactured from a permanent mold casting technique and with increased wall thickness, eliminating the need for exterior shields. The two-piece design allows them to be used with all popular engines by simply changing bolt-on bellhousings.
• Ford C4 (PCE628.1003): This SFI 4.1-approved Ford C4 transmission case comes complete with an adjustable trans-brake release, built-in flexplate shield, and transmission shield to improve your vehicle's performance.

Engineering Features That Set Speedmaster Cases Apart

Speedmaster's automatic transmission cases are built from high-quality aluminum for maximum strength and minimal weight. These heavy-duty cases are available to replace popular stock GM or Ford models and are capable of handling high horsepower. The TH400 case in particular showcases just how deep Speedmaster's engineering goes: features include speedometer and governor provisions, longer band anchor pins captured by oversize bosses, multiple external pressure taps for monitoring circuit pressures, compatibility with all style oil pumps including 8-bolt and vari-pitch designs, heli-coiled bellhousing and oil pump threads, and pre-machined fitment for larger custom planetary gear carriers.

A Brand Built on In-House Manufacturing

Speedmaster is one of the rare companies to produce its own products, with the majority of items entirely developed and manufactured in its own workshops. Speedmaster is the world's only major parts manufacturer to equip cars from standard replacement to Top Fuel Dragsters. That breadth of experience — from street builds to the highest levels of drag racing — flows directly into every transmission case they produce. When you're selecting a case that needs to survive repeated high-power launches, that pedigree matters.

Explore the full range of Speedmaster performance parts or browse all automatic transmission cases to find the right fit for your build.