Took a look around for people who have had a similar diagnostic issue, but can't seem to find anyone with the same problem.

Vehicle: 2007 Ranger Sport 4x4 (lots of miles on her)

Issue: When 4x4 high is engaged, the truck shifts normally into 4x4 hi, and the light on the dashboard lights up normally. However, under load (moderate to high, straight line acceleration) a loud thunk or clunk is heard, and the front wheels disengage from 4wd. A few seconds pass, then the front wheels re-engage into 4wd.

This issue similarly presents in 4 low, with normal 4x4 operation under low-medium engine load, but disengagement of the front wheels from 4x4, coupled with a large thud, thunk or clunk under more moderate engine load.

Anyone encountered these issue before or have any diagnostic tips for a beginner?

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Should add that the re-engagement of the front wheels is also accompanied by a lound thunk or clunk

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2007 Ford Ranger Sport 4x4, 4.0L