Allison 1000 Output Shaft Lock Nut Socket, J-38805

This is the special socket that fits the output shaft lock nut on a 4WD Allison 1000. The nut sits behind the transfer case adapter and is torqued high enough that no standard socket or pipe wrench will move it without chewing up the flats. This one cross references GM 29531231 and J-38805, the numbers the factory service procedure calls out for that nut.

Fitment is 2001-2010 Chevrolet Silverado 2500HD, 3500 and 3500HD and GMC Sierra 2500HD, 3500 and 3500HD, four-wheel-drive trucks running the Allison 1000. You need it any time the transfer case comes off the back of the transmission: rear output seal replacement, transfer case adapter reseal, output shaft or speed sensor work, or pulling the case for a rebuild.

On the bench or under the truck, the sequence is the same. Drop the driveshaft and unbolt the transfer case from the adapter, then stake the shaft so it cannot spin - a holding fixture or a bar through the yoke flange - and put a breaker bar on this socket to break the nut loose. Going back together, the socket lets you pull the nut to spec instead of guessing, which is what keeps the adapter seal from weeping later.

Hardened steel with a black-oxide finish, one piece, no bushings or adapters to lose. It is a single-job tool, but it is the job that stops a transfer case reseal cold if you do not have it.