DIY Install Guide: Rear Differential Breather on 2nd Gen Tundra

A Step-By-Step DIY Installation Guide to Relocating the Rear Differential Breather on 2nd Gen Tundra

If you own a Toyota and do any sort of trails, off-road driving, or live in a city that seems to constantly flood every rainfall, a rear differential breather is a cheap, easy, must-do mod.

For most newer Toyota’s the rear differential breather is a small cap on the top driver’s side of the rear differential housing. Simply put, this cap allows for the differential to get air when necessary to cool down. The cap opens and ingests air to cool down all of the inner components.

However, this can be an issue if you were to hit a deep puddle on a trail or unexpectedly get struck with flash floods on your commute home. While issues may or may not immediately affect you or your rig, the $30 20-minute modification affords you the insurance and peace of mind knowing that in the event the above scenarios occur, you are covered.

Over time, it can also get caked up with mud and road debris, starving the differential of air necessary to cool. So even if you steer clear of deep water, this is a great way to ensure a healthy, clean and functional rear axle for many miles to come. So, let’s dive in (pun intended).

Tools & Materials:

• 14mm wrench
• 12mm wrench
• Flat head screwdriver (or 8mm socket)
• Zip ties
• Scissors
• Teflon tape
• T30 Torx key, bit, or driver
• 1/4″ hose clamps (2)
• 10′ of 3/8″ ID hose
• New OEM Breather
• New OEM Union

Or, purchase the pre-made kit by Yota Shop!

Find it Online:

• Toyota Off Road Vehicle Differential Breather Extension: Check Price

Installation Overview

Here is a quick look at what you need for the installation.

Step 1. Remove Factory OEM Diff Breather

Using your 14mm wrench, start by removing your factory OEM differential breather. My truck is a brand new 21’ so it’s fairly clean and in good shape. Once the stock breather is removed, try to get the surrounding area clean. Place the breather aside as you’ll be re-using it later on.

Step 2. Mount New Union

Wrap a thin layer of Teflon tape around the new union and tighten it down using your 12mm wrench. Expect some resistance as you tighten as the tape will create some tension. You’ll know when it’s nice and snug; don’t hulk it!

Step 3. Remove Drivers Side Tail light

Now that your OEM union is installed, you can run your line.

Before we do that, let’s remove the tail light. The tail light is held in with two (2) easy-to-access T30 Torx bits and metal tabs in retaining clips.

Undo your Torx bits. To remove the taillight, apply equal pressure on the top and bottom with both hands; pull to get the nipples out of the retaining clips.

Step 4. Running Your Hose

Now that your light is removed and your cavity is exposed, you can see straight down to the floor. Drop your hose down and wedge it in between the strut pictured here to hold the line steady while you create your loop and run along with the frame. Run your line how you wish and be mindful to make sure it isn’t in a position that will be pinched by any moving or dynamic parts of the body or frame.

Step 5. Securing Your Hose

As you run the link from the breather section to its ultimate end position, loosely zip-tie the hose along the way. Once you’ve got the line run, you’ll want to make sure you have an excess of hose above the rear differential to create a loop. This loop is important for when your axle is at full droop and extends. The amount of loop you need depends on how much travel your suspension has. If you’re running a long travel setup, you’ll want to have a lot of extra room.

I like to operate with a “better to have it and not need it, than need it and not have it mentality”. So, I chose a generous amount of loop because why not? If it’s tucked well, a couple extra inches of the hose isn’t going to be restricting and may make all of the difference on the trail. Double-check at this point your zip ties holding the hose to the frame are loose; you do not need or want them overly tight.

Step 6. Clamp Hose to Union

Next, clamp your hose to the newly installed union using either a flathead screwdriver or an 8mm socket. Now that your hose is clamped to the union and your zip ties are loosely holding your line along with the frame to the tail light cavity, you can finish this install up!

Now, Clamp Breather to Hose

Depending on the length of the hose you started with, you may or may not need to trim the excess. I started with 10′ and ended with probably closer to 7′ (even with a dramatic loop). Stick your new OEM breather into your line and hose clamp it down. You can use a small flat-head screwdriver to do this or an 8mm socket. I prefer to not over-tighten it and potentially risk cracking or warping the hose so I chose to use a flathead.

Note: During this install, I had the hose attached to the union with the hose clamp loosely wrapped around it so that this step was a little easier. Attaching and removing this hose and stretching the inlet out is not preferred and I like to know my hose is mounted where it needs to be while running the line, building the loop, and cutting the excess hose.

Step 7. Mount the Breather

With the breather now securely fastened to the hose, it’s time to zip-tie the line to your strut. I like the location of the strut because to me, I don’t see myself going that high in the water… ever. Hopefully, and at this location, the breather is easily serviceable in the event it needs attention for whatever reason. Plus, not that it matters because it’s hidden, I think it looks clean in this location.

Zip tie this line tight to the strut. The way I have explained this install is that you want your two key components tight and everything else, loose. Your union and breather should be mounted and mated tightly, but everywhere else in this connection should be loose and floppy.

Final Check

Now, carefully examine your service loop and make sure the loop is still maintained the same way as it was. This is why having too much hose is better than too little. If it looks the same, move on. If it doesn’t, return the loop to where you’re happy with it and tighten your zip tie just a smidge more. Re-install your tail light reversing the steps described above, add more loose zip ties to the frame and hose, and boom; you’re done! Now go drink a Coors Light and find yourself some water to ford!

If you want to confirm your loop is adequate, you have a couple of options to do so:

1. The Smart Option: Jack the truck up from the body to get your max amount of travel out of one side and see if there is adequate length to avoid tension.
2. The More Fun Option: Find something or somewhere to do a flex test as pictured below.

Final Thoughts 

Overall, this install took almost no time at all. The hardest and most time-consuming part is calculating your loop and installing the PTFE tape. It’s a $30 and 20-minute insurance policy for the event I ever need/want to ford water that would otherwise cover my axle and potentially flood my differential. This mod is one of those better to have and not need, than need and not have type things.

Glamorous? No. However, it’s so functional, it’s confusing as to why it didn’t come stock like this.