U340 Planetary Carrier Assembly – Automatic Transmission Planetary Gear Carrier for Nissan. Today we're looking at the U340 and U341 planetary carrier assemblies. The planetary carrier is a core component of the automatic transmission — it distributes torque through the planet gears and directly affects shift smoothness. Worn carriers often show up as noise, slipping or harsh shifting. Our units are machined to OE tolerances, assembled and inspected for runout and clearance