The rear locker is standard equipment for this year. It's one of the reasons I chose this model. I'm fairly certain the ratios are correct, as this is a new issue for me. It has never done this binding up before when I push the button.

I see today that one of my front tires is pretty low. I don't think that would cause it, as the front diff obviously isn't locked, but I'm otherwise out of ideas.

Interesting. I hadn't heard of a viscous coupling before. So this coupling transmits the torque but allows for some slip if it's needed? Is this coupling only for the front axle, or does it apply to both? Does moving the lever engage a non-slip gearset or chain?

I need to read up on this.

Edit to add: Thanks for the introduction. I found this link that provides a good explanation. Viscous Coupling | awd cars, 4x4 vehicles, 4wd trucks, 4motion, quattro, xDrive, SH-AWD, Haldex, Torsen, wiki - How it works

The rear diff locker was never standard equipment on any 4Runner. It was always an additional option from the factory. Airbags are standard (they came in every trim of 4Runner) but rear diff locker was not standard (not every 4Runner received one).

Semantics. It was a standard option. Not really important to the conversation.

The question is whether your truck was equipped with it from the factory or not and if a diff was replaced at some point to the wrong ratio.

Most/all of the rear locker 4Runners are 4.3 ratio front/rear and most of the rest are 4.1 front/rear - so if either the front or the rear was replaced on its own, there could be problems.

There is no viscous coupler in the 3rd gen multi-mode transfer case. Later transfer cases did have a viscous coupler in some configurations. If you are feeling any binding in "AWD" mode (four green wheels lit, no center orange light), there is a problem with your 4WD system. Even on dry straight roads, you should feel no binding or odd behaviors in locked 4WD (orange light - you would feel it when turning and that should be avoided).

-Charlie

The locker is original equipment. It wasn't added later. This rig is stock. Canadian, but stock.

No viscous coupler... I'm both happy and sad about that. I've spent the last hour down a rabbit hole and imagining how I could replace the non-Newtonian fluid myself. Then again, those are expensive.

The binding is happening, but it was minutes and miles apart. I was on the freeway, as I mentioned. I could feel the steering getting stiffer and stiffer and then the 'pop' as it came free.

One thing I didn't mention. This journey started off with me stuck in my driveway. I live on an incline and couldn't get up the hill in 4wd. Naturally, the next thing I tried was the locker. I engaged the rear, but found it was causing too much lateral movement. I was sliding sideways instead of going backwards. So I unlocked the locker and put on chains. This got me out of my driveway and down the road. I removed the chains and started down the road as I first mentioned.

Now, I wonder if my locker never disengaged? I don't think I would feel that in my steering as I had, but it would definitely cause the binding.

Probably a long shot. I'm guessing I have a T-Case issue.

Actually, reading my own response above makes me wonder if I have a front differential issue and this has nothing to do with the transfer case. Could the front be locking somehow? I'm afraid to say that I'm clueless on this vehicle. I just never took the time to learn its components. Is the front diff limited slip, or does it have some other feature that may have failed?

Sorry, but the title of this message cracks me up every time I see it.

If you were on the freeway and felt it, it is unlikely a 4WD issue. Or at least not a normal one. You couldn't turn quickly enough at highway speeds to get 4WD binding.

Try "AWD" mode in a parking lot and see if you have issues there, which should rule out a number of issues (it should drive just like 2WD). Then locked 4WD (center diff) in a straight line. It should still drive 'normal' even on dry pavement until you turn.

The 4WD system should be able to disengage no problems - sometimes when they aren't 'exercised' they get sticky/slow. Worst case for mine is needing to lift the throttle (though that's unfair, my transfer case is manual).

4WD binding would just lead to a bit of tire chirping and needing extra gas to make tight turns - no popping or similar should be felt.

-Charlie

There is one way to know for sure and will take 15 seconds of your time. On your doorjamb sticker, you'll see a gear code. If you've got A03A, it came with 4.10 gears from the factory. If it says anything else, it was built with 4.30 gears.

agree

My 2000 has done the stinky front diff puke twice. Both times after an extended drive in AWD when it was in the 20s the night before, and still fairly cool out.

Only the '01 and '02 get the fancy pictogram with the green or orange lights regarding the state of the 4x4 system. The '99 and '00 guys have to suffer with only a rear locker.

The 99' LTD(Oct 98') + has the 4wd and 4x4 position indicator. I drive with 4wd or 4x4 quite a bit in the summer 90*F / 32*C on backroads for hours on end and at high speeds as well as winter for 6 months, never had a front diff puke oil out.

Great Info Thanks for Sharing !

You are right, my mistake. I assumed the V in Toyota tcase nomenclature meant viscous coupling. It does - but only if the V is at the end. Multimode is a pure open diff.

Later t-cases have a gear type torsen center diff to counteract the open diff. Better than a viscous coupling. Only truck tcase I can think of with the viscous coupler then is in the FZJ80 and Prado 95.