J.A.'s Toyota 4Runner Highlander
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 Extended Rear Differential Breather:

Toyota Union Fitting

Toyota Breather Plug
The factory provides a breather for the front and rear differentials, the transmission and transfer case. This is needed to allow venting which will equalize the pressure in the unit as the temperature inside it changes during useage.
Toyota ships the 3rd Generation 4Runner with the front differential breather already extended up into the engine compartment. If you look in the engine compartment, on the inside of the driver side wheel well you will see a rubber hose capped off with a silver breather at the end.
The probelm with the factory rear differential breather is that it is located right on top of the differential and there is a possibility that water might be drawn inside. The factory rear differential breather is 18 inches above the ground. In most situations this is fine but when taking the vehicle off road many times water may be above that height. When the water level is above the top of your differential case, the hot differential is rapidly cooled by the colder water and air is drawn in to equalize the pressure. If the case is submerged when this rapid cooling occurs and water enters the case rather than air, serious damage will be the end result and is something this modification tries to avoid. Another problem with the factory breather location is that over time dirt accumulates around and in the breather and it may become clogged. If it gets stuck in the open position water is sure to enter and if it gets stuck in the closed position oil can blow by the differential seals.
By extending your breathers you are relocating the point at which air is drawn in to a higher location.
This is how I extended the rear differential breather.
I ordered Toyota part # 90404-51319 'Union Fitting'. This part is made to be used in various Toyotas as an intake manifold fitting for the brake booster vaccum hose. It fits perfectly into the rear differential once the stock breather is removed. You need a 14mm deep socket to remove the factory breather, and a 12mm deep socket for the new union fitting. I used Teflon tape on the threads before inserting it for a nice seal. Next I attached 5 1/2 feet of clear 3/8 inch pvc tubing to the barbed union fitting with a small hose clamp. I ran the hose up the gas tank filler tube, using cable ties, leaving plenty of slack for axle articulation. In order to tie down the top section of hose near the gas filler door you need to temporarily remove the rubber boot around the gas cap. First use a 14mm socket on the nut holding the filler door latch, then remove 2 metal O rings holding in the rubber boot. I capped of the top portion of tubing with Toyota part # 90930-03136 'Breather Plug', again using a small hose clamp. I cable tied it to the gas filler neck and replaced the rubber boot. I choose to keep the breather behind the boot, but you can cut a hole in the boot to bring it further forward if you like. Many people choose to use a cheap clear gas filter instead but either should work well.

Extended Rear Differential Breather Mod

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