i got under my x and noticed that it looked like there was supposed to be a bung or some kind of hose attached to the rear axle. after reading on here i believe that it is the "breather hose". my question is what does this do. i took it to the dealership to get an oil and diff oil change, they didnt say anything to me about the broken part. is this somthing that needs imideate attention or what, i have no idea what it is to be honest so im in need of some major help here.

thanks to everyone who can help

If if is the breather tube, just to the left of the diff housing on the left, looking from the back, it releaves pressure as things turn around in there. It is nessisary to keep water out of the housing. Normally the tube runs from the axel housing up to the body just about the axle. While it may not be an emergency, you should replace it as soon as possible. I would also change out the fluid if you don't know how long it has been missing, just in case there is water in there.

While performing the 3,750 mile service on my wife's 4x2, I noticed that the 4x2 only has a little pressure relief cap on there, instead of a tube.

Also, when I was checking the diff fluid, I could hear pressure release from the diff when I was removing the fill plug. Interesting.

My Fronty only has the relief valve. No tube or hose at all. I understand it is a one way valve.

Haven't climbed up under mine to check. It's pouring rain right now, or I would.

At any rate, after all the water fording we did in Florida, the diff fluid I changed in both of my diffs last weekend was definitely water-free.

2000 has the breather tube, 2004 has the little pressure relief valve, I don't know when the change was made (2001, 2, 3, or 4). Those are the only two years I've looked at in detail.

no one way valve. as the fluid heats up, it expands, and would increase the pressure in the axle, hence the vent. as it cools, it contracts, and will lower the pressure in the axle, if it was a one way valve it would suck air into the axle through the seals at the wheels, hence it is just a vent cap, not a valve. you want to extend whatever is there at least to the level of the floor in the truck. as you ford water, the axle will cool quickly, and without a snorkle of some sory, it will suck the water right off the top of the axle is it is under water.

It surprised me how hot the differential gets... I can barely touch mine after freeway driving... so Xtopher may have a good point.

I believe the "Vent" has a float in it that closes in water. I've seen many people ford water where it got covered and it didn't suck in water. As long as you don't park for a while in a river where the water is to the top of the tires you should be ok.