Why does my speedometer stop working after a T56 swap, and how do I fix the VSS signal?
Here is what the documentation says. Each point links to its source; details depend on your exact computer, harness and transmission.
- TH350 / manual: With a TH350 or manual transmission, the VSS is not required but is recommended. (Performance Systems Integration)
- Gen IV LSA 58X; T56 / TH350 / TH400 / Powerglide / 700R4: PSI recommends using a VSS with a T56 or non-electronic automatic (TH350, TH400, Powerglide, 700R4); without one, stalling during hard braking or an inoperable throttle body can result. (Performance Systems Integration)
- Tremec Magnum: In this install the two VSS wires from the Tremec Magnum ran to the SN74Z module's Sender and Speedo In terminals, with speed calibration done through the module. (MotorTrend)
Confirm against the instructions for your exact parts before wiring. More: Tach and speedometer signals in our tuning guide.
Confidence: medium — sources disagree or are limited; check the sources below.
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Sources
- The Right Way to Wire Up Gauges for Your Classic Chevy — MotorTrend
- PSI Performance Engine Parts Installation Troubleshooting — Performance Systems Integration
- PSI Installation Guide HAR-1099 (Gen IV LSA 58X) — Performance Systems Integration