Shift Kit V/B Repair Kit GM TH400/TH425 1965-Up

The TRANSGO Shift Kit V/B Repair Kit for GM TH400/TH425 transmissions is a comprehensive valve body and shift kit solution designed to restore proper shift quality and transmission responsiveness on 1965 and later TH400 and TH425 automatic gearboxes. This complete rebuild kit addresses the internal hydraulic control issues that develop as transmissions age, providing the critical components necessary to recalibrate shift timing and firmness without requiring a full transmission rebuild.

The kit includes OEM-specification gaskets, separator plate components, and calibrated springs that regulate hydraulic pressure distribution within the valve body. These internal components work together to control when and how forcefully the transmission engages each gear. Over time, worn gaskets leak pressure, and weakened springs allow shift points to drift, resulting in delayed shifts, harsh engagement, or inconsistent performance. By replacing these wear items with factory-correct specifications, the transmission regains its original shift characteristics and reliability. The kit is engineered for drop-in installation, eliminating the need for custom modifications or machine work.

This repair kit serves two primary audiences: restoration builders who want to return a classic vehicle's transmission to original specification, and performance enthusiasts maintaining high-mileage TH400/TH425 units in daily-driven muscle cars, trucks, and hot rods. The TH400 is renowned for durability and remains the transmission of choice for heavy-duty and modified applications. Rather than replacing an otherwise sound transmission, this shift kit extends service life and restores drivability at a fraction of full rebuild cost, making it a practical maintenance solution for long-term TH400/TH425 ownership.