The CAT 320C and CAT 320D<\/strong> are separated by only one platform generation, but the question of whether their swing gearboxes are interchangeable comes up constantly \u2014 in part because CAT’s own parts catalogue lists different part numbers for units that look identical, and in part because dealers and operators give contradictory answers based on individual experience. This article provides a definitive comparison: what actually changed between the 320C and 320D swing gearbox, which components are shared, which are unique to each generation, and how to order a confirmed aftermarket replacement without guesswork.<\/p>\n The CAT 320 series has been CAT’s best-selling 20-tonne class excavator since the 320B launched in the mid-1990s. The 320C succeeded the 320B in 2001 and ran until approximately 2008. The 320D replaced it from 2008 onward, with the 320D2 entering production around 2015. Each generation involved revisions to the hydraulic system, cab electronics, and in some cases the undercarriage and upper structure components \u2014 including the swing gearbox<\/strong>.<\/p>\n For the purposes of swing gearbox replacement, the 320C and 320D represent the two most common variants in the current used-machine market. Both machines are abundant in the working fleet across Australia, Canada, and North America \u2014 making their swing gearbox a high-demand aftermarket part that is worth understanding in detail.<\/p>\n The changes between generations fall into three categories:<\/p>\n The rated swing torque for both the 320C and 320D is in the 14,000\u201316,000 Nm range depending on specification variant. CAT did not significantly change the planetary gear ratio or torque capacity between these generations. If your only concern is torque rating, the two units are in the same class.<\/p>\n<\/div>\n The output pinion tooth count and the ring gear module changed between certain 320C and 320D variants. A 320D swing gearbox pinion may not correctly mesh with a 320C ring gear even if the flange bolt pattern appears similar. This is the primary reason why 320C and 320D units are not treated as interchangeable in OEM parts documentation.<\/p>\n<\/div>\n The swing motor mounting flange and port layout was revised between some 320C and 320D configurations. In most cases, the motor interface is sufficiently similar that cross-generation replacement is feasible with minor hose modification \u2014 but this must be confirmed before ordering, not assumed.<\/p>\n<\/div>\n<\/div>\n![\"CAT](\"https:\/\/planetarygeardrive.top\/wp-content\/uploads\/2026\/03\/Swing-Gearbox-for-Construction-Machinery3-1024x1024.webp\" "\\"\\"")
<\/p>\n<\/div>\nThe CAT 320 Platform: A Brief Overview<\/h2>\n
What Changed Between the 320C and 320D Swing Gearbox<\/h2>\n
Interchangeability Table: 320C vs 320D<\/h2>\n