Tundra 4WD seems to be slipping and loud clunk when disengaging

I have had increasing difficulty disengaging 4WD and hear a loud clunk when shifting between D to N to R to disengage. This weekend on snow it seemed to engage but alternately power or free-wheel, as if something was slipping. It disengaged easily without the loud clunk. I could feel the front wheel pull or coast in a rhythmic pattern.

 

The front differential is open, so the front wheels spin independently. The wheel with the least amount of resistance/ traction will spin while the other is freewheeling.

 

Loud clunk only when it disengages? That’s typical when on pavement as the 4wd tends to bind and clunks when it disengages. Keep it on loose ground (i.e. dirt, snow, gravel, etc.). These trucks typically only disengage smoothly when new on a harder surface like pavement. Allowing it to give a little when disengaging will keep it happy.

 

It is possible that is what I was feeling. I drove it more on wet snow today and it was not as pronounced. Previously I have only used 4WD when pulling my boat out of the water on our gravel launch. I first noticed it when backing out of a turn-around in 6 inches of snow. After that, I only used it if I could not climb a hill in 2WD. When stopping to put in 4WD it was most notable as I started from the slope in snow. A single wheel slipping may be what I was feeling.

 

Before this weekend I have only used 4WD when pulling my boat from our gravel launch. When I get it out I turn 4WD off and the light just continues to blink without disengaging. I move it from D to N to R and eventually after two or three cycles it will pop out with the clunk.

 

Sounds like it needs to be exercised more often. Owners manual calls for 10 miles/month but I bet very few people do that.

 

I get a loud clunk during disengage every time if I'm coasting/not under load. Feels similar to rolling over a broomhandle or something. This is something myself and several others have bitched and complained about, going on for years now. Are you sure you just never noticed it before?

Meanwhile, there's a whole sticky thread for 4WD diagnostics if you want to dig.

 

The noise varies from a popping sound to the sound of hitting metal with a hammer. It seems to be loudest when I have the most trouble with disengaging. What I didn't notice before was the apparent traction-coast-traction effect in heavy snow when stuck going uphill in 2WD, and then turning on 4WD. I am going to change the transfer case lube to see if that helps.

I have read some discussions of the noise and concluded it was somewhat normal, but grew concerned when I believed there was a slipping in and out of gear connection.

 

Understood.

Yeah, it wasn't pretty what came out of my front diff when I changed my fluid. It was more grey (like oak tree bark) than anything for the first 1/3 of what came out. No obvious signs of water contamination, just ... silvery goodness. I literally have no idea what the previous two owners did with the truck during the 59,000 miles they put on it. Truck is just over 80k original miles now.

I honestly do not remember the "THUD" on disengage when I first got the truck. I'm pretty religious about putting Toyota's recommended 10-miles-per-month with 4HI engaged. I guess it's possible I always disengaged under load ... until the first time I didn't? Therefore I didn't hear the THUD.

But maybe it's a recent occurence, and it happens with dirty contacts, or maybe there's something that requires lube in the transfer case? That's been on my mind a lot. I know the steel post that gets actuated on has three settings/slots and that rod gets pushed/pulled, in/out, while shifting between 2HI/4HI/4LO, and in my head, I've been kicking around the thought that maybe the thunk is the sound of that rod begrudgingly slamming into place because there's 20 years of gunk built up in there somewhere?

Anyway, here's the community brain on 4WD diagnostics/maintenance/etc --> https://www.tundras.com/threads/1st-gen-4wd-issues-diagnosis-prevention-guide.149189/

Big kudos to @FiatRunner for assembling it all. See his "Step 4", the last (or 4th) video shows the actuation rod I'm talking about.