ICT Billet TH400 Speedometer Plug for Turbo 400 Chevy Transmissions — Bare Billet Aluminum, Includes Bolt & O‑Rings

ICT Billet's billet aluminum speedometer plug for the TH400 (part 551908) fills the speed sensor port on Turbo 400 transmissions when you use a GPS or don’t need an electronic speed output.

This machined plug is designed specifically for Turbo 400 (TH400) transmissions used behind small-block Chevy engines such as 305, 327, 350, 383 and common V8 displacements like 5.0L and 5.7L. Manufactured in Wichita, Kansas from aerospace-grade, USA-produced billet aluminum, the assembly includes the plug, retaining bolt, and O-rings for a complete, leak-resistant installation on applications that do not require a factory speed sensor.

What does this plug do and when should I use it?

The plug blocks the electronic speed sensor opening on TH400 transmissions so fluid stays sealed and the transmission functions normally without a speedometer drive. It's appropriate when you replace the mechanical or electronic sensor with a GPS speedometer or when the vehicle's setup never included a speed sensor.

• Seals the transmission speed sensor port on TH400 models
• Prevents fluid leaks without a stock speed sensor installed
• Used with GPS/aftermarket speedometer solutions
• Includes necessary bolt and O-rings for sealing

How is this plug made and why does that matter?

The part is machined from aerospace-grade billet aluminum sourced in the USA for dimensional accuracy and corrosion resistance compared with lower-grade cast or stamped alternatives. Precision machining and included sealing hardware reduce the risk of leaks and simplify installation in a tight transmission recess.

• Made from 100% USA-produced billet aluminum
• Aerospace-grade material for durability and corrosion resistance
• Precision tolerances for a proper port fit
• Comes with matching bolt and O-rings for a reliable seal

Which transmissions and engines is this compatible with?

This plug is designed for the Turbo 400 (TH400) family of Chevrolet transmissions and fits common small-block Chevy installations. It is targeted at vehicles built around SBC engines including 305, 327, 350, 383 and popular 5.0L/5.7L V8 applications where the stock speed sensor is omitted or replaced.

• Specifically fits TH400 (Turbo 400) transmissions
• Commonly used with Chevy small-block engines (305–383 ci)
• Works with 5.0L and 5.7L V8 conversions and swaps
• Not intended for transmissions that require a functioning speed sensor

How do I install it and what hardware is included?

Installation is straightforward: remove the original speed sensor or cap, fit the O-rings, insert the billet plug into the port, and secure it with the supplied bolt. No special tools beyond standard hand tools are required, but ensure the transmission is cool and clean to avoid contaminating fluid passages.

• Includes plug, retaining bolt, and O-rings
• Standard hand tools needed for installation
• Clean port and cool transmission recommended before fitting
• Torque bolt to spec to avoid over-compression of O-rings

Who is this for? The ICT Billet TH400 billet aluminum speedometer plug is aimed at builders, restorers, and hot-rod owners who run Turbo 400 transmissions without a speed sensor or who use GPS/aftermarket speedometers. It suits anyone who wants a reliable, American-made solution machined from high-quality billet aluminum and supplied with the sealing hardware needed for a clean installation.