The Advance Adapters TH400-Atlas Adapter (SKU AS-6400) is a 4.25" spacer adapter built specifically for GM TH400 transmissions (also compatible with the 4L80E) that have a 4.5" output shaft stickout. This is a fitment-specific measurement, so confirming your transmission's output shaft stickout length before ordering is worth doing — Advance Adapters calls out the 4.5" figure specifically as the application this adapter is designed for.
What's included:
- GM T400/4L80E Gasket (716510)
- Adapter, TH400 to D300 (51-6400)
- H.H.C.S. 3/8-16 x 1-1/2" Grade 5 Zinc (723723)
- Lock Washer, 3/8 Zinc (723704)
This is a lean kit — gasket, adapter, and hardware, nothing extra — built for a specific TH400/4L80E-to-Atlas fitment where the 4.5" output shaft stickout matches. Since the source listing is short on detail beyond the stickout spec and BOM, that's the extent of what I can verify; if you have Advance Adapters' fitment chart or install sheet, it'd be worth cross-referencing before publishing to confirm which specific Atlas or D300 applications this pairs with.