Question: Rear Diff Breather

[HuntRunner]

I was looking to do this mod and was wondering about the parts suggested in the write-up:
1. 90404-51319 Union
2. 90930-03136 Plug, breather

(I have a 2003 4Runner)
I am guessing that the union is just a connecting unit for the fuel line to the diff. But, what is the Plug, breather (other than what it says)? I guess my question really is how does it work? Does it operate the same as the existing factory breather, just located higher up? Does it allow air flow in both directions?
Thanks

 

[jharris2]

I was looking to do this mod and was wondering about the parts suggested in the write-up:
1. 90404-51319 Union
2. 90930-03136 Plug, breather

(I have a 2003 4Runner)
I am guessing that the union is just a connecting unit for the fuel line to the diff. But, what is the Plug, breather (other than what it says)? I guess my question really is how does it work? Does it operate the same as the existing factory breather, just located higher up? Does it allow air flow in both directions?
Thanks

You're right on target. The breather is similar to the one that is on the truck already but the connector is easier to put on the fuel line.

The breather is like a relief valve -- when the pressure inside gets too high, it lifts up a bit and lets a bit out. As far as I am aware, it's not designed to allow air to go the other direction.

 

[Casper]

Im still trying to figure out why people would want a breather to allow fluid out vs just cooling the diff with maybe a finned cover...while i know that fins could inhibit some off road ability, im sure that someone would be able to make one. I know that I would purchase one.

 

[jharris2]

Im still trying to figure out why people would want a breather to allow fluid out vs just cooling the diff with maybe a finned cover...while i know that fins could inhibit some off road ability, im sure that someone would be able to make one. I know that I would purchase one.

Not to release fluid, but air.....

 

[Casper]

Not to release fluid, but air.....

ok...but still, wouldnt one want to cool the diff as a proactive step rather than vent as a reatice step?

 

[Thai]

ok...but still, wouldnt one want to cool the diff as a proactive step rather than vent as a reatice step?

It's cheaper doing the breather extension...A LOT cheaper! And even if i have a finned differential, i still would want a breather valve.

 

[Casper]

It's cheaper doing the breather extension...A LOT cheaper! And even if i have a finned differential, i still would want a breather valve.

True.....

I guess ill look into doing it......damn, i have so much to look into.

 

[TeCKis300]

The purpose of the breather is not to cool the diff in anyway. It is simply a way to prevent pressure from building up inside the casing.

As the differential reaches normal operating temperature, air will naturally expand. Without a relief or "breather", pressure will build up. If pressure is allowed to build, it will exert forces on the axle seals and other seals possibly wearing them unessarily or pushing diff oils and lubricants out.

The idea behind extending the breather is to prevent contaminates from entering the diff or plugging the breather when fording rivers, mud and such.

 

[HuntRunner]

Ok....I may be thinking to hard on this but...if the valve is to relieve pressure by letting air flow out, won't there at some point be a cooling of the diff., creating a vacuum of air going back in??? If the valve is only a one way valve, how does the air get back in?