88-90 Gm Th400 375 m40

The 88-90 GM TH400 375 M40 automatic transmission shift kit from B and M AUTOMOTIVE is engineered for enthusiasts and professional mechanics seeking improved transmission response and control on classic GM muscle cars and performance vehicles. This shift kit addresses the inherent lag and soft shift feel of stock TH400 transmissions, delivering crisper gear engagement and faster acceleration feel during hard launches and spirited driving. Whether you're building a street machine, preparing for weekend track duty, or restoring a vintage Chevy with modern performance expectations, this kit transforms the driving experience by firming up the transmission's behavior without sacrificing reliability.

The 88-90 GM TH400 375 M40 operates by recalibrating transmission fluid pressure and shift valve timing to reduce converter slip and increase shift firmness across all three gears. The kit modifies the pressure regulator and shift valve assembly, allowing the transmission to hold gear longer under load before upshifting, which translates to improved off-the-line bite and mid-range torque feel. This precise hydraulic tuning maintains the TH400's legendary durability while eliminating the mushy, delayed response typical of stock setups. The compact design weighs only 0.88 lbs and fits within the transmission pan area, making installation straightforward for mechanics familiar with TH400 service procedures.

This shift kit is ideal for 1988–1990 GM TH400-equipped vehicles, including Camaros, Firebirds, Corvettes, and full-size trucks seeking performance enhancement without a complete transmission overhaul. Installation requires dropping the transmission pan and removing the valve body—a task well within reach of home garage builders and professional shops alike. The kit works seamlessly with stock converters and engine outputs, and it pairs exceptionally well with modest cam upgrades, intake modifications, or light turbo setups where you want the transmission to keep pace with improved power delivery. Verify your vehicle's model year and transmission identification before ordering to ensure proper fitment.