Rear diff breather mod....question

So I'm going out on Saturday to have some fun at an off road park with some of the local Texas Tacoma guys. A few of them were wanting to do the mod before we got there because of some shallow water tanks they have there.

I'm about to do the mod too but then I got to thinking...

The breather is to allow gases to leave or enter the pumpkin as it heats/cools. Great, fine, I get that. So then I started thinking about the tubing and the volume of air contained in the tube and inside the actual differential itself.

What volume of air do you think is inside the differential? A quick flashback to physics reminded me that liquids don't expand or contract due to heat and but that's a property of gases. So really all the breather is for is that tiny bit of air in the diff that expands and contracts right?

Would you not be able to just add a longer tube (containing a larger volume of air inside) and cap the end? The amount of air leaving the diff and entering the sealed tube couldn't possibly pressurize the tube hardly at all. Do you see what I'm thinking? Is it even needed to have the other end open? It all just seems a bit excessive to me. Can I get a guru in here to explain?

 

I'm not a physics guru either so some of this may not be 100%. I'd say it is easier to leave the other end with the breather valve. The air in the tube will also respond to temperature fluctuations and expand/contract. Not only could you have too much outward pressure, you could have too much inward (vacuum) pressure given the right circumstances (I don't know what they would be exactly). I doubt the seals and gaskets are designed for any sort of high pressure difference. Maybe if your tube acted kind of like an inflatable bladder so that it could inflate/deflate as the diff heats/cools. The only problem is determining how much air should be in the bladder at a nominal temperature so that there is enough room for expansion/contraction.

 

That's a good point! I didn't think about that initially. I suppose something like a water balloon on the end would be ideal in terms of allowing pressure out and in. Not that I'd put anything like that on my truck exposed to the elements (water balloons actually make excellent caps for bare/unused RCA ends).

I'm still going to get the breather assembly and install it. But I was just curious how much pressure we're talkin.

 

Someone makes a accordian style piece that's inflates and deflates

 

If it's not dead ended no pressure will ever build up. On the other hand if it is blocked somehow pressure will simple build up till the seals start to leak. A pound or two psi would probably make them start leaking. They even put those ends on the front where the hoses are much longer. I see your point but it's not worth trying to engineer around it.

 

Just as a reality check, if water gets up to your gas cap, your truck is screwed anyway, so it's probably easier not to worry about it and just do the tried and tested method

Edit: meant to say cap

 

It is an easy mod... the hardest part is removing the spare tire! See the link in my sig. below for how I did it...

The factory breather does NOT let cool air back in, only hot air out. What most of us (who did the mod) did was do what Toyota does on the front differential... put a 2 way breather up high. You want to break the vacuum that could occur when driving into cool water with a hot diff. and prevent mud/water from entering the diff. past the axle seals...

 

Why on earth did you remove the spare tire when doing this mod?

Anyway OP, it's easy, but definitely put a two way breather on the far end. The seals are the most vulnerable thing, as others have said.

I mounted mine next to the gas filler, but now that I think about it, it makes the most sense to mount it on the filler neck inside the actual fender, as that's by far the most weather protected area.

 

I have a shell over the bed and mounted the breather in the forward cubby hole compartment on the drivers side...allways dry and out of the weather.

 

Umm, so I could easily access the breather and install the tube without jacking up the truck... then photograph it for you all... This was what another had done before, so I was following the advice given here, and it made it easy. Did you even click on my link to see?

 

We had about 3 people do this mod yesterday with no jack, no tire uninstall and the hardest part was getting the breather on the 1/4 in fuel line... took maybe 30 mins each, and beers were being drunk at the same time

 

Yes I did. I understand easier access to the valve stem for the spare, so killing two birds with one stone makes sense.

Other than that, I'd think dropping the spare to do this mod would be more trouble than it's worth.

 

Yeah I was wondering about that, because the breather which your HOW-TO calls for is

$6 90930-03136 Toyota Breather Plug - 90930-03136

90930-03136 which is way different than the factory breather on the rear diff. The two way breather almost seemed like it doesn't allow any air in or out, I tested it by blowing through it...lol

 

The opening is small, but apparently enough for the differential to breath with.

The breather is the same as they use on the front differential...

It is 'way different' because it is a barbed two way breather (for the end of the 3/8 tube) and not a threaded one way breather that is on the differential.

 

Sure, forgot about doing the spare tire mod at the same time! My previous Tacomas had the valve stem pointing down... weird. Perhaps they though it would bring more business to dealers if the low air light went on, and all the owners could do was check the 4 tires on the truck, and not check the spare!?