Frequently Asked Questions

Swapping a TH400 to a 700R4 in a 4×4

This swap is usually done to gain overdrive while retaining the existing transfer case, but the spline difference is the main issue. Verified facts A GM TH400 normally uses a 32-spline output. A standard GM 700R4/4L60 uses a 27-spline output. The NP208 was offered in different versions, including: 32-spline input behind a TH400 27-spline input behind a 700R4 Therefore, a 700R4 will not simply slide into the 32-spline NP208 originally installed behind a TH400. Twisted Torque’s TH400-to-700R4 NP208 adapter kit addresses this by using a new output shaft and spud shaft with a 32-spline female input, allowing the TH400-style NP208 to be retained. The listing identifies the application as model years 1985–1991. Transmission Depot’s matching listing confirms those kit details. Other installation considerations The 700R4 must be disassembled to install a replacement output shaft. Crossmember placement may change. Front and rear driveshaft lengths must be measured after installation. Cooler-line placement may change. The 700R4 requires a correctly installed and adjusted TV cable. A torque-converter lockup connection or lockup kit is needed. Gear ratio and tire size should be considered because the 700R4 has a deep 3.06:1 first gear and overdrive. The transfer case must be identified as the correct NP208 version before ordering.

Ford AOD to Early Bronco Dana 20

This conversion allows a 1966–1977 Early Bronco to retain its Dana 20 transfer case while gaining the AOD’s four-speed automatic overdrive. Verified facts The adapter assembly fits 1966–1977 Bronco Dana 20 transfer cases. The standard adapter is approximately 6 inches long. The kit uses a replacement AOD output shaft. Installing that output shaft requires transmission disassembly. The kit retains the original-style Bronco transfer-case mounting arrangement. A T-style transfer-case shifter is the recommended and listed setup. The completed assembly is approximately 1½ inches longer than the original V8 drivetrain arrangement. Crossmember relocation or modification is required. Driveshaft length and front-driveshaft clearance must be checked.

Can I keep my existing transfer case when changing transmissions?

In many 4×4 swaps, yes, as long as an adapter is available for the exact transmission and transfer-case combination. Some kits connect the two using an adapter housing, while others require a replacement transmission output shaft or transfer-case input gear. Always confirm compatibility before purchasing because a matching bolt pattern does not guarantee that the shafts and splines will fit correctly.

Will a transfer-case adapter change my driveshafts or crossmember?

It can. A different transmission or adapter housing may change the overall drivetrain length and mounting position. This can require crossmember relocation, transmission-mount changes, driveshaft shortening or lengthening, and transfer-case shifter adjustments. Install and position the transmission, adapter and transfer case before measuring for driveshaft changes. Also check front-driveshaft clearance around the transmission pan, exhaust and crossmember.

4L60E to 4L80E 4x4 Ext Housing Adapter and Shaft

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