Installs the pressure switch laminate discs and seals in GM 6L80, 6L90, 6L45, 6L50 and Gen 1 6T70/6T75 units to fix hard 1-2 shifts without a new TEHCM.
A Silverado, Sierra, Camaro, CTS, Traverse, Acadia, Enclave, Malibu, Equinox or Impala that slams or flares on the 1-2 shift, or throws pressure switch codes and drops into a failsafe gear, is often quoted for a new TEHCM. In many of those trucks and cars the electronics are fine and the fault is a cracked film disc or a hardened seal in one of the module's pressure switches. This kit gives you the four installation tools for that repair plus five seals and five laminate discs, which is enough to redo the switches on one module.
On GM's first-generation six speeds the transmission computer and the solenoids share one assembly with a row of hydraulic pressure switches, and Sonnax explains that each switch is plumbed to a clutch circuit. When pressure rises, a thin laminate disc presses down and breaks the contact; the computer reads which switches have opened to know which clutch has actually applied and how quickly. That timing drives shift adapts. A disc that wrinkles or splits, or a seal that lets oil bypass, sends a late or false signal, and the computer responds with a harsh or flared shift, a code, or a failsafe gear. Sonnax rebuild kits exist for exactly these switches on the 6L45, 6L50, 6L80, 6L90 and Gen 1 6T70 and 6T75.
Check fluid level first, then watch the switch states on a scan tool that can display them while you drive. A switch that never changes state, or changes at the wrong time, is the one to suspect. Measure the circuit as well, since a broken trace or terminal will not be fixed by new discs. Our 6L80 Escalade shift problems guide explains why so many trucks get a module they did not need, and the 6L80 Camaro shift problems guide covers line pressure testing and the adapt reset.
The kit is listed for the GM 6L45, 6L50, 6L80 and 6L90 rear-drive transmissions and the first-generation 6T70 and 6T75 front-drive units, and it is made to work with the 124740-30K style seal and disc pack. Later second-generation 6T70 modules use a different design, so match the module to Gen 1 before ordering. Manufacturer part number B-124740. Refill discs and seals for more modules are in our 6L80 pressure switch repair kit. If you are not sure which unit you have, send us the year and VIN. More parts are on the 6L80 transmission parts page.
Disconnect the battery, remove the module with the valve body, and work on a clean, static-safe bench. Pick out each old disc and seal without scratching the switch bores. Set the pusher piston, drop in a new laminate disc, and work the laminate tool around the full circle so the disc lies flat with no folds. Lubricate each new seal with Dexron VI and push it home with the seal plunger and installer. Rebuild all the switches, not just the one with a code, since the films age together. Reinstall, torque the valve body bolts in sequence to the service figure, fill with Dexron VI, then reset adapts and complete a relearn drive. If the module itself has failed electrically, the 6L80 control valve body with TCM replaces both assemblies.
| Fits | GM 6L45, 6L50, 6L80, 6L90, and 1st-gen 6T70 / 6T75 transmissions |
| Works with | F/124740-30K pressure switch seal and disc rebuild pack |
| Kit contents | 1 pusher piston, 1 seal plunger, 1 seal installer, 1 laminate installation tool, 5 seals, 5 laminate discs |
| Rebuilds | Enough discs and seals for one TEHCM unit |
| Job it solves | Hard or flaring 1-2 shifts from failed TEHCM pressure switch seals, without replacing the module |
| Manufacturer part number | B-124740 |
Often, yes. If the module electronics test good and the fault is in a switch disc or seal, rebuilding the switches restores normal readings. It will not fix a failed circuit board, solenoid or terminal.
GM 6L45, 6L50, 6L80 and 6L90 rear-drive units and the first-generation 6T70 and 6T75 front-drive units. Second-generation 6T70 modules differ.
It includes five seals and five laminate discs, enough for one module. For more modules, add a refill pack of discs and seals.
Rebuilding the switches does not change the module calibration, so no programming is required. Reset transmission adapts and drive the vehicle through a relearn so the computer relearns clutch timing.
Replace them all. The discs see the same heat and fluid, and a second one is often close to failing.
