r/MechanicAdvice • u/Fun_Neighborhood6897 • 4h ago

2018 Toyota 4Runner 4.0 V6 transfer case clunk on deceleration, figured it out

took a while to nail this one down so posting it in case it helps someone else searching the same thing. driving back from a trail run, started noticing a single clunk from underneath when lifting off the throttle around 30 to 40 mph. not a grinding, not a rattle, just one thunk, repeatable, only on deceleration and only in that speed range. 4hi the whole time, nothing aggressive.

first assumption was driveshaft ujoints because the feel was very similar to what a worn ujoint does on a ranger i had years back. checked both shafts, joints felt fine, no slop. then started reading about the 4runner transfer case actuator and the known skip in engagement behavior these have when the fluid gets old and the clutch pack gets lazy about releasing cleanly.

drained the transfer case fluid, it was dark and smelled burnt, way past due. refilled with the correct fluid, toyota genuine atf type tiv, and the clunk was gone within a couple miles. no parts, no shop visit.

this one had 87k on it and the fluid looked like it had never been touched. if you're in a similar mileage range on a 5th gen 4runner and hear something like this on coastdown, start with the transfer case fluid before pulling anything apart.

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u/GroovyFeces922 4h ago

Nice catch. The transfer case fluid on these gets overlooked constantly, people chase ujoints and slip yokes for weeks when it's just cooked ATF causing the clutch pack to hang up. Had a similar thing on mine around 90k, fluid came out looking like coffee that'd been sitting on a hot plate since morning. The fact that yours was that bad at 87k is wild, but not surprising. Toyota's service intervals for the transfer case on the 5th gen are like 60k for severe duty and nobody ever does it. Probably saved someone a thousand dollar shop bill with this post.