Marshall 9220 Hall Effect Speedometer Sender

The Marshall 9220 is a Hall effect speedometer sender designed to bridge the gap between older mechanical-drive transmissions and modern electronic speedometer heads. It threads into the speedometer port on GM and Mopar transmissions — TH350, TH400, 700R4, A727, and similar units — replacing the mechanical cable drive with a clean 16-pulse-per-revolution electronic signal. This is a common requirement on restomod builds, street rods, and any classic vehicle being upgraded from a mechanical needle gauge to an electronic dash or GPS-augmented speedometer system.

Construction is straightforward and purpose-built: the Hall effect sensor reads the rotation of the transmission's speedometer drive gear and converts it to a clean digital pulse signal on the white wire output. The 7/8-18 in. thread matches factory GM/Mopar spec, the 0.104" driver key engages the existing drive gear without modification, and the quick-disconnect harness keeps the install tidy. Operating range of 8–30 VDC and a temperature tolerance down to -40°C means this sender is reliable year-round in any climate. The main installation consideration is confirming that your speedometer head is calibrated for a 16-pulse input — get that wrong and your speed readings will be off by a fixed ratio regardless of how well the sender is installed.