2008 Tundra Crewmax, 4wd clunks but doesn't engage- help!

(Hi, first post here so bare with me)

Bought my 2008 Toyota Tundra Crewmax (5.7) used in Nov. 2019

The 4wd has worked flawlessly up until recently, well..
last winter it started having trouble engaging unless I was rolling. Once I found it to be not (completely) broken, I never used it again until recently.

I went to engage 4HI, and I can hear an audible clunk, but the light continues to blink and not engage properly.

Prior to this issue I discovered that the previous owner had used the wrong fluid in the front & rear diffs causing a horrible metallic grinding noise whenever the traction control came on. I've replaced the rear dif fluid with amsoil gear oil which solved the issue. the front I haven't gotten to yet because the drain bolt is seized (I'll have to do the ol' suction method eventually but that's a different day's problem)(ps. will it do damage to drive around like this for now??)

My main question is:
(1) Is it possible the previous owner potentially used the wrong transfer case fluid? Is that where my problem may be coming from? Thus would a simple fluid change possibly solve my issue? (god forbid nothing is damaged from it)

(2) If I am hearing the clunk, is it a possibility it's the actuator or no- because I'm hearing movement of "something"?

Looking for a place to start getting this issue resolved! Thanks in advance to anyone that can help.

 

Welcome to the forum! There are actually two actuators. One in the transfer case and one in the front differential. It’s possible one is engaging but not the other. Having the wrong fluid may or may not be causing an issue. Even having the wrong fluid spec shouldn’t cause grinding. I mean I guess if you put the wrong kind of fluid it could. The fluid, if unknown, should be changed before using the 4wd system. The actuators can be bench tested off the vehicle for proper operation. They can also be roughly tested for function on the vehicle. If you have a way to get the vehicle on a lift or all 4 wheels up with jackstands safely you can test the 4wd system for what’s engaging and what’s not. The actuators can get corrosion on the contact areas from moisture over time.