Allison 1000 6-Speed Valve Body Shift Repair Kit

TransGo part number TGOSKALLISON-JR, a V-Repair kit for the control valve body in Allison six-speed units. The manufacturer lists it for 2005-2010 applications, which covers the Allison 1000 six-speed behind the LBZ and LMM Duramax as well as the medium-duty chassis that share the same valve body casting. It is a repair kit, not a full valve body -- everything in the box goes into the housing you already have on the truck.

The problem it addresses is bore wear. Allison valve bodies are cast aluminum, and the bores that the pressure control and shift valves shuttle in wear oval over a few hundred thousand miles. Once the clearance opens up, control pressure bleeds past the valve instead of holding, and apply timing drifts. On the road that shows up as a harsh or flaring 1-2, a delayed engagement into drive after the truck has sat, erratic shift quality when the fluid is hot, and eventually a TCM-commanded limp mode. A shop will often chase that with fluid and a filter first, then a solenoid, before finding the wear is mechanical. Re-establishing the fit in the bores costs a fraction of a replacement valve body.

On the bench: drain the pan, pull the filter, and drop the valve body -- on most GM pickups the Allison valve body comes out from underneath without pulling the transmission. Work on a clean, lint-free surface and lay the separator plate down flat, because the Allison body carries loose check balls and small springs that will roll away the moment the halves separate. Follow the TransGo instruction sheet in the kit for which valves and springs get changed and in what order; do not guess from memory, because the sheet is calibration-specific. Flush the bores clean of aluminum dust before anything goes back in, torque the body bolts to the factory sequence, install a new filter and fill with the correct spec fluid, then clear codes and let the TCM relearn adaptives with a scan tool that supports Allison functions.

Confirm what is actually in your truck before ordering. The 2005 model year is a split -- many 2005 trucks left the factory with the five-speed Allison, and the six-speed did not become standard until the following model year. Check the transmission tag or the RPO code rather than the model year alone.