Allison 1000/2000 Selective Shim and Spacer Kit 29536407

This is the complete selective shim and spacer kit for the Allison 1000 and 2000 series automatics, Allison part number 29536407 (also listed as 29536407-DF). It is new surplus genuine Allison stock, sold as the full assortment rather than a single thickness, so you have every selective on the bench when you measure instead of ordering one and waiting three days for it.

These are the transmissions behind the 6.6L Duramax in Chevrolet Silverado and GMC Sierra 2500HD and 3500HD trucks, plus the 1000 and 2000 series in medium duty chassis, buses and box trucks. During a rebuild the selectives are what set clutch pack clearance on the C1, C2 and C3 packs and control main shaft end play. Every core is different, so the correct shim can only be picked after the pack is stacked and measured.

The bench procedure is the same every time: stack the clutch pack dry with the pressure plate and the apply plate in place, set a dial indicator on the top plate, lift the pack and read total travel. Compare that reading to the Allison clearance spec for that pack, then pull the selective out of this kit that brings the measurement into range and recheck before the drum goes back in the case. End play at the main shaft is checked the same way with the indicator on the shaft nose. Skipping this step is the reason for a lot of comebacks: a pack that is too tight drags and burns the frictions, and a pack that is too loose shift flares and hammers the steels.

Keeping the full assortment on the shelf is what makes an Allison rebuild a one day job rather than a two day job.