How-To: Rear Axle Vent Mod

Here’s my version of the common rear differential breather mod.


  1. Toyota OEM Union 1/4″, 90404-51026, $5.94*
  2. Mann Complete In-Line Fuel Filter, 33001, $4.99
  3. Toyota OEM plug, Breather 1/4″, 90930-03136, $5.27
  4. 1/4″ Fuel Line Hose, $5.06
  5. 1/4″ Hose Clamps, $2.99
  6. 14mm open wrench
  7. Clean rag w/degreaser
  8. A few black zip ties

The whole job literally takes less than 10 minutes, and parts came out to just under $20 for everything. This is an easy job, you don’t even have to jack the vehicle up, just make sure you have all the parts you need first.

NOTE: After looking at the fitting options I noticed that the Nissan version “Breather Tube Connector”, part #38323-C601A works but it is a smaller diameter connector, like 1/8″ or 3/16″ maybe. I opted for using 1/4″ sizing which meant using the Toyota OEM part instead.

All the parts I used to do the diff breather mod.

STEP 1: First, clean away the area around the OEM breather using a rag and your choice of degreaser. Use the 14mm open wrench and remove the OEM breather cap. The Toyota OEM union will thread right in. Note: there will be 2-3 threads exposed when the Toyota OEM union is threaded in, this is fine; you will not get it flush with the axle housing, but this is not a problem as it threads in more than enough.

Old one-way breather on the left, new Toyota union barb on the right.

STEP 2: Attach fuel tubing and secure with a 1/4″ hose clamp. Run the hose along the side of the right-side brake line, and secure with zip ties (leave some hose slack as shown in the photo below.)

Fuel hose used, kept some slack in and zip tied it to the nearby brake line.

STEP 3: From here many people have their own version of how and what to do after this; some people just zip tie the bare hose and and call it done. Some people  run the hose all the way to behind the right-side taillamp and install an in-line filter at the end of the hose. I chose to have the filter in-line, with another piece of hose afterward. As for the in-line filter, I mounted mine on an unused bracket that you can find near the center of the factory crossbar right above the axle.

In-line filter high up under the truck bed, using an unused OEM bracket on the cross bar.

STEP 4: I attached another piece of hose on the in-line filter and ran it to a second unused bracket (on the same crossbar, but to the right), as shown in the photo below.

Side view photo of the installation; photo taken from the left side, under the bed, looking at the right rear shock area.

STEP 5: Finally, for extra moisture prevention I installed a matching 1/4″ Toyota breather at the end of the hose; the Toyota breather is a 2-way (no spring) to allow for air expansion and contraction. I liked this way better than the smaller diameter Nissan version, which has a spring in the cap making it exit-only.