The Advance Adapters TH400-Atlas Adapter (SKU AS-6401) is a 1.25" adapter built specifically for GM TH400 transmissions with a 1.5" output shaft stickout. That measurement is the key fitment detail — it's shorter than the AS-6400 kit's 4.5" stickout spec, so it's worth confirming your transmission's exact output shaft stickout before choosing between the two.
Unlike the AS-6400 (which adapts to a D300), this kit's adapter is machined for a Jeep NP231-pattern short adapter interface, so it's suited to swaps targeting that transfer case pattern.
What's included:
- Bolt, 3/8-16 x 1-1/2" S.H.C.S. Zinc (723740)
- GM T400/4L80E Gasket (716510)
- Adapter, TH400 to JP NP231, Short (51-6401)
This is a lean kit — gasket, adapter, and hardware — built for the specific TH400-to-NP231 fitment where the 1.5" output shaft stickout matches. As with the other TH400 adapters in this line, confirming the exact stickout measurement against your transmission is worth doing before ordering, since Advance Adapters offers several lengths for different applications.