What is needed to bolt a TH400 to an LS engine and get a VSS signal to the PCM in a C10?
Tach and speedometer signals
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- The ECM is programmed to expect 40 pulses per revolution from the VSS, typical of automatic transmissions. (applies to LS Control System kit)
- The LS Control System harness is designed to plug into the output speed sensor of 4L60 and 4L80 transmissions, which have a 40-pulse output. (applies to LS Control System kit; 4L60 / 4L80)
- Late-model GM transmissions used an internal speed sensor outputting 128,000 pulses per mile. (applies to late-model GM automatics)
- The SEN-01-128 is NOT for use with transmission shift computers or ABS systems.
- Published figures differ: Conflicts with the Dakota Digital product page, which calls the SEN-01-128 output a direct replacement for the stock GM internal speed sensor for ECM use.
Transmission control
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- Lokar's TH400 electric-kickdown instructions (INS0004, Rev. 05/08/14) are designed around the Lokar SRK-4000 carburetor bracket/return-spring assembly; a cable-operated switch box mounted under the transmission trips at WOT and energizes the detent solenoid, and the switch-box wiring is not polarity-sensitive (either wire to either terminal).
- Lokar mounts the TH400 kickdown switch box under the transmission with 5/16-18 x 1.25-inch bolts and 1/4-inch spacers, cuts the cable housing to the bracket-to-bracket distance plus 1 inch, and adjusts at WOT with the inner wire pulled tight: the throttle must reach WOT without interference and no cable slack may remain at WOT.
- The TH400 detent solenoid may have one or two terminals. Leave about 1/2 inch of excess inner wire beyond the stop for future adjustment.
- Lokar's TH350 kickdown bracket installs under the two rear driver-side intake-manifold bolt heads, with the cable housing snapped into the bracket's square opening; proper adjustment lets the engine reach WOT without cable interference while the cable cannot be pulled any farther at WOT.
- Lokar's universal TH350 cable adjustment procedure: release the housing latch, hold the throttle at WOT, and relock the latch.
Confirm against the instructions for your exact parts before wiring. More: Tach and speedometer signals in our tuning guide.
The TH400 bolts to the LS block except for the 2 o'clock hole, which the LS block doesn't have; keep the donor trans bolts and locating dowel pins. With a dished truck flexplate, a converter pilot adapter ring centers the converter in the LS crank, and the OEM converter bolt circle may need the flexplate holes opened slightly with a rat-tail file. For VSS, press an ACDelco 24202711 40-tooth reluctor wheel onto the TH400 output shaft (heat it gently and press it on without its clip) and mount a two-wire VSS sensor. Run the wires to the PCM's VSS High/Low pins as a twisted pair (about 9 twists per foot), shield the run with foil tape along the frame rail grounded at the frame, and add a heat shield near the exhaust.
Check this first:
- Check the converter stall sticker (stock truck converters are about 1,830 rpm)
- Confirm dowel pins and all bolt holes are aligned before torquing
- Verify converter bolt holes line up with the flexplate
Careful: An unshielded or poorly routed VSS signal can cause erratic speed readings and drivability problems.
Based on what we've seen work across our own builds, our friends' builds and the wider LS community, reviewed by our lead shop tuner (over 20 years of LS and LT tuning experience). Every combination is different, so use at your own risk and check our safe tuning limits before any wide-open pass.
Go deeper
Check this first
- Check crank bore vs converter nose - order the right adapter.
- Plan the VSS: 40-tooth wheel + sensor on the output shaft.
- Verify flexplate/converter bolt pattern matches.
Try this, then this
- 1) Bolt TH400 to LS (skip the 2 o'clock hole); crank adapter for the converter nose.
- 2) ACDelco 24202711 40-tooth reluctor on the output shaft + VSS sensor.
- 3) Wire VSS to the PCM; verify speed signal on a test drive.
How you know it's fixed
- Trans bolts flush, converter engaged, PCM sees vehicle speed, speedo works.
Still not fixed?
- No VSS signal usually means sensor gap or wiring - check the sensor air gap first.
Every option we know of
| Maker / product | Part # | Fits | Price | Where | Status / notes |
|---|---|---|---|---|---|
| ACDelco 40-tooth VSS reluctor wheel | 24202711 | TH400 output shaft | verify current | Buy GM dealers, RockAuto, newparts.com | Current production Tooth Quantity: 40 - confirm before ordering |
| eBay/aftermarket Crank/converter nose adapter | varies | LS crank bore to TH400 converter nose | about $22 | eBay (~$22 reported) | Available Verify engagement depth |
| Dakota Digital Speed sender alternatives | SEN series | If reluctor wheel route doesn't suit | about $100-150 | Dakota Digital dealers | Current production Match pulse output |
Prices are approximate as of September 2026. We list every option we know of, including small shops and used parts we can't link to. Confirm fitment with the seller.