What Transfer case fluid does this vehicle use?

Okay. That helps. Then yes it looks like that chain is slapping the case. It is unlikely to be slipping because those think chains will damage the teeth of the gears and you would see that.

Take a look at the case and surrounding parts and see if there are any witness marks that would be the chain slapping.

If you see nothing, then I suspect the transfer case if just worn out.

That is very common with AWD vehicles and there is no info on rebuilding them.

I am sure you can, but you would have to find parts and then work through it. MB says to replace them.

One thing you need to do before you do anything more than replace the fluid is make sure all four tires are the same size. I don't mean the same size that is stamped on the side. I mean they actually measure the same.

Use a string and wrap it around each tire and make sure they are within a quarter inch of each other circumference wise.

If they are not, they damage the transfer case and the only way to fix that is to replace it.

As for the fluid, if it came out fast then that is ATF. No question.

Yep. So that was the next step. If there are no signs of slapping and the teeth are okay the chain is stretched.

However, that is rare so if you have a chain coming, just lay them on a table to compare them. They should obviously be the same length.

Let us know because that would be interesting to see if this is the issue. Thanks

That is great news. Something drastic had to have happened to that because I had only seen a handful of chains stretched and none of them were that thick.

Great find. Clearly you have good instincts. I will remember that for next time.

Thanks again for the updates and the picture.

Interesting. So, if there are more than one then I suspect what happens is the chains are more sensitive to heat. So, if the fluid is not maintained then it gets hot, and that chain will stretch. Heat is the cause of the expanding of any of these chains but since your fluid was black, I suspect that it completes the story because heat is what causes the fluid to turn dark.

Thanks again.

When the fluid deteriorates it loses a lot of its properties including the ability to dissipate heat. So that means the unit gets hotter. As the unit gets hotter, the fluid breaks down more and it turns into a cycle.

So, as the unit gets hotter because the fluid is broken down, the metal gets malleable and when it is put under tension, the metal stretches.

Timing chains fail the exact same way. Keep in mind, this is rare, but it does happen enough that we should keep an eye on it.

Other people say that a chain will stretch under heavy loads, but I never bought into that because it doesn't make sense. The load is on the joints and not the turning components like this. In order for them to stretch under load the two mounting points (sprockets) would have to be moving in order to stretch it and they are stationary.

The connection points all through the drive train. The u joints, input and output shafts, etc.

The chains are turning fast but if centrifugal force were enough to stretch the chain, then all chains would stretch. So even though they are spinning fast they are not going to stretch without something else happening to them.

What I mean by load is pulling a heavy trailer or going up a lot of mountains. This type of load has no effect on timing chains or transfer case chains but is hard on u joints and input shafts.