Rear diff may be going what are your thoughts on this

212K Prerunner 2WD LSD

About two weeks ago while merging onto the freeway at around 70 mph, I started feeling a heavy buzzing. I dropped it from D to 4 to see if it was the torque converter, but there was no change in RPMs and the buzzing continued. On the way home, after stopping for a while, it didn’t happen again.

The next morning, making a right-hand turn at about 10 mph, the buzz came back for a few seconds. A few minutes later it returned, so I shifted into neutral, but the buzzing stayed before eventually fading out. Since then I haven’t felt that heavy buzz again, but something still feels off from time to time.

I’ve gone over the entire undercarriage: checked for heat on the rotors in case of a sticky caliper, inspected the driveshaft, tires, and wheel bearings (all seem fine—no play, no grinding). Differential fluid is present. But I did notice something odd: while the truck was on my lift, I spun the rear tires with it in park and heard a clicking. In neutral, no clicking. The clicking I was hearing was very audible. That makes me think the issue may be internal to the rear diff.

Lately the buzzing has turned into more of a humming, and it feels like it’s coming from the rear diff. I couldn’t find a decent used low mile replacement locally, so I’ve decided to have my current diff rebuilt. A local Toyota shop, not a stealership is going to look at it in October. My concern is just making sure it lasts until October and doesn't grenade on me. The cost of rebuilding versus buying a rebuilt unit is nearly the same just paying for labor which I'll be more than happy to pay for to keep me from doing it by myself and trying to find time when I'm not working and having it on my lift for extended time.

Thoughts on what's happening, I'm pretty sure my diff is nearly shot

 

I used to dismantle cars years ago, not a mechanic but I know my way around a vehicle and I could just be really wrong. But from past experience that when you hear loud clicking the clutch packs are on their way out or there's issues in the pinion or spider. The fluid was pretty dark when I pulled the drain plug, I didn't find any metal but I also didn't pull the cover yet or change the fluid. I've just been so tied up with work and family. I work swing shifts and I'll finally have some time off next week to put it back on the lift and see what I can find. I just did the left rear bearing 2 months ago and now I'm kicking myself for not draining the diff since I was already there. Nothing leaked out when I pulled the bearing so I didn't need to add any fluid but now I probably should have and either contaminated the diff oil or maybe it's the clutch packs or something worse, dunno yet but also if it is worse I'm not against doing a full Rebuild. Money isn't the issue, it's just finding time to get to it which is why taking it to a shop would be so much easier than trying to find time. Dunno, I'm an over thinker but such is life lol. I'll.

 

What? You dropped down a gear and the RPM stayed the same?
Doesn't sound right to me?

Again, not sure how this can happen in Park?

What? If you pulled the drain plug?
The fluid came out. Did you reuse the old fluid?

There is no cover to pull.
You pull the whole 3rd member.
If you have a lift and hand tools, you can swap the 3rd member yourself.
Especially if you managed to do rear bearings.

 

Parts of this just dont make sense. The tires don’t spin when in park. Other things too don’t make sense. In any event I doubt your problem is your diff. And I wouldn’t replace it at this point. Sometimes you just have to say wtf and take it to a shop to diagnose the problem. After they diagnose it you can decide if it’s something you want to mess with or let the shop deal with it.

 

When it's off the ground, you can spin the tires.

 

I may have wrote some of that wrong, when I dropped it down to 4 there was no significant change in RPMs, yea you could feel the RPMs shift but it's wasn't like the convertor was struggling, it shifted fine.

Also I have a lift, you can spin the tires when it's in the air. Maybe I worded that wrong as well.

When I pulled the drain plug all I did was unscrew it until fluid came out so I tightened it back up. I was short for time when I did that.