V2 vs V3 Gearbox Shimming Process

Question:

What is the difference between a V2 and V3 gearbox shimming process?

Answer:

The shimming process between V2 and V3 gearboxes shares the same fundamental goal — minimizing gear play while ensuring smooth rotation — but the physical differences between the shells create some notable variations in the process.

The V2 gearbox, commonly found in M4 and MP5-style platforms, uses a two-piece shell design. This means you must shim each gear individually and repeatedly test-fit the shell halves together to check for binding or excessive play. The process can feel repetitive since you cannot observe all three gears under load simultaneously until the shell is fully closed.

The V3 gearbox, typically found in AK and G36-style platforms, also uses a two-piece shell but features a different bevel gear placement. The bevel gear in a V3 sits in a slightly different position relative to the motor grip angle, which can affect how much shimming is needed between the bevel and shell floor. Additionally, the anti-reversal latch design differs slightly, so technicians should confirm it seats correctly after shimming is complete.

In both versions, the standard shimming order is bevel gear first, then spur, then sector. The key difference technicians notice is that V3 shells sometimes allow marginally easier access during reassembly due to their wider body design, while V2 shells require more patience when aligning the spring guide and trigger components simultaneously.

Regardless of the gearbox version, using quality feeler gauges or consistent shim thicknesses (commonly 0.1mm, 0.2mm, and 0.3mm) ensures accurate results for either platform.