Most vehicles made during the 20th century rely on a mechanical cable (usually attached somewhere on or near the transmission) to drive the speedometer readout. The cable connects to a mechanism inside the speedometer to convert that cable’s rotation into the movement of your speedometer needle.
While that method is pretty reliable, it’s not always the most accurate.
More importantly, if you’re planning a modern transmission swap, there’s a good chance it won’t use a mechanical drive cable and instead have a vehicle speed sensor—which means your original speedo will no longer work.
Don’t fret though, because the gauge gurus over at Speedhut have an absolutely ingenious solution to both the speedometer accuracy and compatibility issue with the SPEEDBOX Speedometer Adapter module.
The small SPEEDBOX unit installs inconspicuously behind your dash or under the hood. From there, it connects to either your modern transmission’s vehicle’s speed sensor (VSS) or, thanks to the included antenna module, a satellite GPS network. On the other side, you attach a short speedo drive cable (sold separately) from the box into your original speedometer.
The SPEEDBOX then reads that electronic data from the VSS or GPS, and converts it into a mechanical movement that drives your stock speedo.
Speedhut says its SPEEDBOX comes calibrated for most domestic (U.S.) speedometer drives that use 1,000 rotations per mile, but it’s fully adjustable from 170 to 1,650 turns per mile to suit more unique applications as well.
The box itself just needs a good 12 vdc power source and, better yet, it doesn’t require a subscription to receive GPS signals. The drive output cable uses common 7/8″-18 thread with a 0.112 inch drive output square. You can see detailed install instructions here.
All told, if you’ve got a modern transmission swap planned and want to retain your stock gauge cluster—or if you simply want a more accurate speed reading—the Speedhut SPEEDBOX is how you do it.
Get details on pricing and availability by clicking the part numbers below:
And if you want to see a SPEEDBOX module in action, watch one get installed in a vintage DeLorean DMC-12 in this video below:
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