The Wide Open Design TH400 to Atlas Transfer Case Top Mount Adapter is engineered for builders who want maximum drivetrain protection, improved undercarriage clearance, and cleaner packaging in extreme off-road applications. Unlike traditional bottom-supported adapter configurations that leave the transmission vulnerable to rocks, ledges, and hard trail impacts, this design allows the drivetrain to be supported from above. This keeps critical components tucked higher into the chassis and away from the abuse that rock bouncers, Ultra4 cars, crawlers, and trail rigs experience underneath the vehicle.

Machined in-house from 6061 aluminum, this adapter is designed specifically for TH400 4WD transmissions with 1.375" of output shaft stickout and directly replaces Advance Adapters part number AS-6401. This is the same style of functional drivetrain packaging Wide Open Design relies on in custom off-road builds where durability and clearance matter.

Includes:

• WOD TH400 to Atlas Top Mount Adapter
• Hardware for Atlas transfer case mounting
• Designed to replace Advance Adapters AS-6401

Specifications

• Designed for TH400 4WD transmissions
• Fits 1.375" transmission output shaft stickout
• Compatible with Advance Adapters Atlas transfer case applications
• Replaces Advance Adapters AS-6401
• Machined from 6061 aluminum
• Manufactured in America
• Top-mount drivetrain support configuration
• Increased drivetrain and underbody clearance
• Improves exhaust and skid plate routing options
• Helps protect drivetrain from bottom-side impacts

Fitment

• Fits GM TH400 4WD transmission applications
• Designed for Atlas transfer case setups using AS-6401 style adapter configurations
• Requires 1.375" output shaft stickout from the transmission case
• Designed for custom off-road chassis, Ultra4, rock crawler, and buggy applications
• Works well in high-clearance drivetrain and skid plate configurations
• Provides improved exhaust, crossmember, and undercarriage clearance compared to lower-mounted adapter systems
• Verify transmission output shaft length and transfer case compatibility before installation

Tech Insight

Traditional TH400 to Atlas adapter configurations often place the mounting structure and drivetrain support underneath the transmission, leaving critical components exposed to rocks and trail impacts. By moving the support structure above the drivetrain, this adapter helps protect the transmission and transfer case while improving overall ground clearance.

The compact top-mount design also gives builders more flexibility when routing exhaust systems, designing skid plates, and packaging suspension or chassis components around the drivetrain. In aggressive off-road applications, every inch of clearance matters, and keeping the drivetrain tucked high in the chassis can significantly improve durability and breakover performance.