DIY Rear Diff Breather 3rd Gen Tacoma

Rear Differential Breather on 3rd Gen Tacoma

Keep Water Out Of Your Diff – Parts List & How To

Well first off, what exactly are we talking about here?

The differential has 2 main purposes, the first is to translate power from the driveshaft to the wheels, the second is to prevent binding when the wheels turn at different speeds. When the temperature changes inside the rear differential, the breather allows the hot vapors to “breathe” via a one-way valve.

However, when you cross streams or deep mud puddles, there is potential for contamination to occur. Even if your truck seems to run fine after crossing, you won’t know the damages that may have occurred until later.

For the 3rd Gen Tacoma, the breather is located on the top-left side of the rear differential (aka the pumpkin) and is 18 inches above ground level (with stock tires).

This is a short and simple mod that takes between 1-2 hours, depending on your skill level, and can save you thousands in potential repair fees in the future.

No drilling required!


Rear Differential Breather on 3rd Gen Tacoma - Tools

Materials Required

Tools Needed

  • Drill + Adapter for Socket (Optional)
  • Ratchet Wrench (Optional)
  • 14mm Wrench
  • 13mm Wrench
  • 10mm Wrench/Socket (Optional)
  • 2 1/2″ Wrench/Socket (1 to ratchet the bolt + 1 to hold the nut in back)
  • Philips Screwdriver
  • Wirecutter
  • Utility Knife: (Optional)

Step 1. Remove Driver’s Tail Light

What's A Rear Differential Breather & Why Do I Need To Relocate It?

There are 2 bolts that you will need to unscrew with a 10mm ratcheting socket. Remove both of these bolts and lay them aside.

After you put the screws aside, pull the tail light straight back towards you in a parallel fashion. It should pop out of the sockets located on the left and then you can let it hang. (Shown in the image to the left above.)

Note: There’s no need to disconnect the wiring. If you’re worried about damaging the wires, unplug the 3 electrical sockets connected to the tail light. You will then be free to lay it aside.

Locate Where On Tail Light Housing To Run Tubing Through

What's A Rear Differential Breather & Why Do I Need To Relocate It?

Above, you can see the location of where the new rubber tubing will go through (behind the tail light housing) and where you will eventually relocate the breather extension.

Step 2. Prep New Union

Rear Differential Breather on 3rd Gen Tacoma

Prepare the new union (Toyota Part# 90404-51026) by wrapping the threaded part with Teflon tape. This is to make sure that nothing leaks in/out when you replace the breather on the rear differential.

You can either insert the union into the fuel line now or later. I chose to do it now because I found it a bit difficult to fully insert the union into the tube since it’s really snug. You can add grease at the ends to make it easier.

Alternatively, you can install the union first into the rear differential and then shimmy the fuel line tube on top of the union and clamp it down.

Step 3. Remove Old Breather

What's A Rear Differential Breather & Why Do I Need To Relocate It?

If you’re having a hard time accessing this part of your axle, drop the spare tire and jack the truck up to get more room.

Do not forget to chock your tires and set the e-brake. If you choose not to, you can still crawl underneath and remove the old breather. It will be a bit tight depending on your size.

You will need a 14mm wrench to remove the old breather from the rear differential.

Before completely removing the old breather, clean the area around it to prevent debris from falling into the differential. Then insert the new union in place of the old breather and tighten down using a 13mm wrench.

Note: The union will not tighten down flush to the differential body. Use the hose clamp and slide down over the body of the union and tighten the clamp with the Phillips screwdriver, do not overtighten.

Step 4. Run Tubing

What's A Rear Differential Breather & Why Do I Need To Relocate It?

Begin by routing your new extension up and away toward the rear of the truck. Pictured on the right is another angle of the new extension as it travels towards the tail light.

Leave Enough Slack

What's A Rear Differential Breather & Why Do I Need To Relocate It?

Run the fuel line tube along the frame of the truck towards the driver’s tail light, you should see the opening from the first step.

Leave enough slack so that the axle has room to travel up and down without putting tension on the fuel line. Zip tie the fuel line tube to the existing cables and make sure that it’s not in the way of any suspension components, such as leaf packs, etc…

Next, zip tie the fuel line tube to the existing hole to further secure it. Then use the wire cutter to clip the excess from the zip ties.

Step 5. Insert Breather & Mount

What's A Rear Differential Breather & Why Do I Need To Relocate It?

Pull the fuel line tube from the last step and insert the hose clamp. Then, add some grease to the breather and insert it to the end of the fuel line tube. Once it’s in, you can use the clamp to tighten it over the body of the breather. Make sure not to overtighten.

Next, use the 1 sided clamp or cable clamp and clamp it over the existing hole, as shown in the image to the right above. 

Insert the bolt through the front and then pair it with the washer and nut in the back and tighten down snugly but not too tight. You will need to have 2 ½” wrenches, one to ratchet in the front and one to hold the nut in place in the back. If you choose to use existing nuts and bolts that you have on hand, make sure it’s stainless so it will not rust as easily.

Finally, you can pop your tail light back in. Make sure it’s lined up and then push in, you should hear a click when it’s properly seated. Then you can screw the 2 bolts back in with a 10mm socket.

Final Thoughts

This is a fairly simple mod to do for peace of mind.

I would highly recommend it since it doesn’t take too much time and can save you from a costly repair due to a contaminated rear differential from crossing water deeper than 18”.

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10 months ago

1/4″ hose is too freakin small. Thanks for wasting my time and $$

1 year ago

My ’17 TRDSp diff breather will not unscrew, it just turns. Any suggestions on this?

11 months ago
Reply to  Matthew

Shows 14mm nut head in the diagram. You turned that nut head counterclockwise [as seen from above] and it did not unscrew or loosen up?

11 months ago
Reply to  ForTheWin


11 months ago
Reply to  Matthew

One of the reasons that tells me that it should unscrew like a bolt or spark plug, is because of the union that he points you at in amazon is simply threaded like a bolt.

Toyota Union.jpg
1 year ago

Should you use Teflon tape on the threads?

11 months ago
Reply to  Robert

I would use white plumbers teflon tape, absolutely. I use teflon tape on all threaded fluid plugs. and fill port bolts as well. I don’t have to over-tighten them as a result, and they stay nice and sealed up without risk of seizing.

2 years ago

thanks for the excellent write up. just did this on a 21 tacoma and I really appreciated the parts list with amazon links.

2 years ago
Reply to  krud

Happy to help! Thanks for reading.

Chase O'Loughlin
3 years ago

Is the breather you used any different than the stock breather?

Timothy Neil
4 years ago

I think this is an excellent modification that anyone can do. I highly recommend this to everyone who takes their rig off-road.

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