TH400 Extreme Duty Forward Drum & 300M Input Shaft 35-Spline

Take your GM TH400 transmission to the next level with this premium heavy duty forward drum and 300M input shaft combo. Engineered for high-power street, strip, or off-road use, this kit addresses the critical failure points of stock components with a focus on strength, precision, and reduced rotating mass.

Brand:	Speedmaster
Part Number:	PCE623.1028.01
Part Type:	Automatic Transmission Drum
Transmission Drum Material:	High-strength chromoly steel
Sprag Assembly Included:	No
Quantity:	Sold as a kit.

Heavy Duty Forward Drum

• Constructed from high-strength chromoly steel – providing exceptional durability without the weaknesses of cast iron or aluminum. 
• Lightweight design – 3 lbs lighter than stock and nearly the same weight as an aluminum drum, without compromising strength. 
• Oversized 28-tooth shaft-to-drum spline – significantly stronger than the factory design, addressing a common failure point. 
• Enhanced clutch engagement – features dual clutch splines (28 vs. 14) for better support of clutch separators. 
• Precision-machined lightening holes – reduce rotating mass and align with input speed sensors in aftermarket cases. 
• Optimized design – includes ribbing and internal diameter reduction at the middle seal area for further weight savings. 
• High-RPM checkball capsule included – prevents pressure drop at 5500+ RPM for consistent clutch performance. 
• No middle seal required – compatible with clutch volume spacer kits if fill/drain time needs adjustment.  
   

300M Extreme Duty Input Shaft 

• Made from ultra-tough 300M steel – heat-treated for exceptional resistance to twist and fracture under extreme torque. 
• 1-1/8" diameter, 35-spline design – the strongest configuration that fits within a stock-style stator tube. 
• 35% stronger than standard 1" shafts – built for serious racing and high-horsepower abuse. 
• Compatible with aftermarket drums using 28-tooth internal spline – ensures secure engagement with heavy duty drum.  
   

Installation Notes: 

• Input shaft requires a 35-spline turbine hub in the torque converter. 
• Must be used with a large-diameter stator support tube.