Eric,
First, the 3rd gen 4runner comes from the factory with 2 extended breathers ALREADY installed. One is for the front differential, and the other for either the transmission or transfer case (not sure which). You can see these two breather hose/cap by looking into the engine bay on the driver's side...it is the along the wheel well. You should see two hose with two silver caps side by side.
However, for whatever reason, the rear axle does NOT have an extended breather. Good news is that it is easily done (see below)...it would be very difficult to do the front differential and transfer case. Luckily, Toyota did that for us already.
The rear axle, instead, has a little breather cap (withOUT the hose) on top of the axle. The silver cap acts as a one-way valve. When the axle housing gets hot and pressure builds up, the cap pops open, releasing the gas and then closes down to prevent water from getting in. HOWEVER, in theory, this cap can malfunction, especially when you have mud/dirt sticking to it. This can happen if you off-road often or cross streams often. And if it malfunctions, then water/mud can get into the differential housing. That would be bad. All theory because i have not heard of anyone having problems with it...however, to be on the safe side, read below.
Anatomy of the Land Cruiser breather cap (same for 4runner):
The rear axle breather cap is on TOP of the rear axle housing...to the DRIVER'S side from midline. The breather has a silver cap. I don't think anything else looks close to it on the axle housing.
Some have advised to drop the spare tire to give you more room to work with. My local mechanic was nice enough to let me use his bay!
The two main parts from Toyota are:
1. 90404-51319 Union
2. 90930-03136 Plug, breather
Should not cost you more than $15 bucks.
The other parts are from your local Autozone/etc.:
1. 3/8" fuel line hose...about 5-6 ft (i picked 6 ft)
2. 1/4" - 5/8" hose clamps (get a few of them)
3. Cable ties or Zip ties
You can use this link from 4x4Wire's TrailTalk Forums
to do a search on all the discussion on this topic:
http://www.4x4wire.com/cgi-bin/ultim...earch_forum=13
Just type in "diff breather."
For me, i ran the fuel line hose all the way up to the INSIDE of my left (driver) taillight. It goes OVER (on top of) the frame. Run it in front of the rear bumper and into the driver's side taillight housing.
Two important things to remember:
1. Leave enough slack in the fuel line hose for the axle full articulation;
2. BUT, do not leave too much slack that the fuel line hose at ANY POINT dips...that is, the line should not bend down at any point! The fuel line hose should always go UP. This is to prevent any pooling of the differential fluid and cause clogging in cold weather. By running it upwards, if any oil collects in the line, it'll drain back into the diff.
Hope this helps...and enjoy many future water crossings!
EDIT: Here is a video to explain why this mod is so important:
http://video.google.com/videoplay?do...ta+truck&hl=en
