Forklift Automatic Transmission Forward Gear 31421-GE00A — Nissan 1F2 / PA25W Series

The 31421-GE00A is a forward gear for Nissan 1F2 and PA25W series automatic transmissions used in Nissan FJ02-FJ05 forklifts. In an automatic forklift transmission, the forward gear is engaged by a hydraulically-actuated multi-plate clutch pack that is pressurized by the transmission control valve body when the operator selects “Forward” on the directional control lever. This gear features a hardened involute tooth profile with a 20-degree pressure angle and shot-peened tooth root fillets — the shot peening induces compressive residual stress in the tooth root that increases fatigue life by approximately 40% compared to un-peened gears, critical for forklift applications where the forward gear experiences approximately 85% of all transmission operating hours (forklifts spend the vast majority of their duty cycle traveling forward). The gear is machined from case-hardened 20CrMnTi alloy steel with a surface hardness of HRC 58-62 and a case depth of 0.8-1.1mm, providing the wear resistance needed at the clutch pack spline interface.

Replacing a forward gear in a Nissan 1F2 automatic transmission requires complete disassembly of the transmission gear train. Before removing the gear, measure and record the axial end-play of the forward clutch pack with a dial indicator — this measurement (typically 0.50-0.80mm) must be restored on reassembly by selecting the correct thickness snap ring from the available sizes (incremented in 0.10mm steps). Using the original snap ring without measuring end-play is the most common cause of premature forward gear failure, as excessive end-play allows the gear to hammer against the snap ring during directional changes, causing the snap ring groove to peen over and the snap ring to dislodge. The gear bushing inside the gear bore must be replaced simultaneously — a worn bushing will allow the gear to tilt on the shaft under load, concentrating tooth contact on one edge and causing accelerated tooth pitting. Common failure symptoms: transmission slipping in forward but operating normally in reverse (forward clutch pack wear), a rhythmic “tapping” noise in forward at low speed that disappears above 1,500 RPM (worn gear bushing), and metal particles in the transmission oil pan with a copper-colored appearance (bushing material indicating gear bore bushing failure).

This gear fits Nissan 1F2 and PA25W automatic transmissions in FJ02, FJ03, FJ04, and FJ05 series forklifts. Verify OEM number 31421-GE00A on your transmission parts catalog before ordering. For related Nissan transmission components, visit our Forklift Hydraulic Transmission section.

Technical Specifications

• Part Number: 31421-GE00A
• Transmission: Nissan 1F2, PA25W Automatic
• Gear Type: Forward Gear, Hydraulic Clutch-Engaged
• Material: 20CrMnTi, Case-Hardened HRC 58-62
• Clutch Pack End-Play: 0.50-0.80mm (Snap Ring Selected)
• Application: Nissan FJ02-FJ05 Forklifts

Compatible Forklift Models

Each gear is inspected for tooth profile accuracy and case depth, packed in rust-preventive packaging, and ships within 1-2 business days. 12-month warranty. Browse our Forklift Hydraulic Transmission catalog.