Spicer ES066-7B 2-3 Synchronizer Kit 101-464-3XR

This is a complete replacement synchronizer for the 2nd/3rd shift position in the Spicer ES066-7B seven-speed manual transmission, the back-taper design found in medium-duty Navistar/International and other commercial trucks. It is World American part 101-464-3XR and crosses to Spicer 101-464-3X and Navistar 2500246C, so check the number on your old unit or your parts book before you order.

Why it gets replaced: a worn 2-3 synchronizer shows up as grinding going into 2nd or 3rd, a gear that needs double-clutching to engage, or a transmission that pops out of 2nd or 3rd under load. The back taper on the gear teeth is what holds the sleeve engaged; once the cones and taper wear, the truck starts jumping out of gear on the pull.

On the bench: drain the case, pull the transmission, and tear the mainshaft down to the 2-3 position. Inspect the mating gear clutching teeth and cones along with the synchronizer; worn or rounded teeth on the gear will chew up a new synchronizer, so replace anything damaged at the same time. Install the new assembly with the correct orientation, reassemble, and refill with the lubricant Spicer specifies for the ES066.