Differential positive pressure

[plcfcng]

When checking the differential on my new to me 2001 sport I noticed a slight pressure escaping form the fill plug as I unscrewed it. I ended up taking out the vent pulling the pulling apart the cap off finding the hole to be clear I found the cap to the outside of the bore to be very close so I took a tiny file and put a small grove in it to allow pressure to equalize. I spoke with my friend who is a Tech for a local Toyota dealer ship he says they are all like that. So my question is why would it be designed like this with as much of a problem that 4Runners have with axle seal problems. :thanks:

 

[mtbtim]

It sounds like to me your breather was just hanging up a bit. I've taken off the drain plug off many of the rear diffs on these rigs and never heard an escape of pressure. That breather works as a one way valve. When enough air pressure builds up in the diff to overcome the strength of the spring in the breather, it opens to let the pressure out and then closes. I think you should pull your ABS sensors on the ends of the axle housing and take a peak in there to see if gear oil has gotten past the seals. With the rear end jacked up, you can turn the wheels as you look in the sensor hole. It's actually easier to get your head in the there to look if you remove the wheels. You'll see the ABS tone ring and it will work like a water wheel picking up gear oil in that cavity between the seal and the bearing.

I suggest you buy yourself a new breather, or better yet, perform the extended breather mod.

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[pluton]

Continuing on from mtbtim said, are you sure that the hissing sound you heard when you cracked open the filler bolt was pressure escaping, OR was it the sound air going in?
Do make sure your breather vent allows air pressure to escape the the diff heats up.
I actually like the idea of the original one-way valve, as it allows air to escape when heat builds up, but then maintains a slight negative air pressure when it subsequently cools off.
If you don't feel the need to extend the breather to a higher location (what the "pros" do), you could purchase and install a new valve...they're pretty cheap, last I checked.

 

[gamefreakgc]

Continuing on from mtbtim said, are you sure that the hissing sound you heard when you cracked open the filler bolt was pressure escaping, OR was it the sound air going in?
Do make sure your breather vent allows air pressure to escape the the diff heats up.
I actually like the idea of the original one-way valve, as it allows air to escape when heat builds up, but then maintains a slight negative air pressure when it subsequently cools off.
If you don't feel the need to extend the breather to a higher location (what the "pros" do), you could purchase and install a new valve...they're pretty cheap, last I checked.

Yup, around $10. Just replace the breather and drive happy. Better than having to re-do the seals!

 

[plcfcng]

Yes I am sure that the differential was under a slight pressure as I removed the drain plug I removed it slowly in case it was over filled and removing the vent I got the same results. As described above stating the vent is a one way valve that would be incorrect. Vents are put in to allow the vessel to allow pressure to equalize also helping minor moisture to be pushed out as the case warms up. As I mentioned earlier these differentials are prone to axle leaks why promote a condition that aggravates this condition. The spring under the cap would not be designed allow venting as pressure increases by its design as I can see. Yes it only a 10 dollar part putting on a new part that does not have a good design is kind of what these forums are designed to reflect.:usa2:

 

[mtbtim]

Yes I am sure that the differential was under a slight pressure as I removed the drain plug I removed it slowly in case it was over filled and removing the vent I got the same results. As described above stating the vent is a one way valve that would be incorrect. Vents are put in to allow the vessel to allow pressure to equalize also helping minor moisture to be pushed out as the case warms up. As I mentioned earlier these differentials are prone to axle leaks why promote a condition that aggravates this condition. The spring under the cap would not be designed allow venting as pressure increases by its design as I can see. Yes it only a 10 dollar part putting on a new part that does not have a good design is kind of what these forums are designed to reflect.:usa2:

Hmm, interesting. I've had these breathers off and have blown into them to check for their proper function. It takes a fair amount of positive pressure to get the mechanism to open up. I assumed that you are overcoming the spring pressure to open the valve and then when the air pressure decreases the valve closes. This makes sense to me. Why else would the breather have a spring? As designed, this breather could technically be submerged. But, as you're fording a creek crossing and the breather was open at the time you submerged the rear diff, the rapid cooling would close the breather and possibly suck in a little water. A worse scenario is the breather is stuck open and then there would be a constant path for water to flow in.

I guess maybe I should tear one of these apart to take a better look at how they are constructed. So OP, when I'm blowing into the breather and it's taking a fair amount of pressure to get have it escape, what am I overcoming if it's not the spring?

 

[plcfcng]

If you take the breather apart you will find small spring under the cap but when you blow in it it does not unseat anything. So if you need to keep water out it's best to move it higher to keep all water out. My point is with the axle seal issues having positive pressure would only promote leakage. I did not design the vent but the spring may have been put there to stop it from rattling around I know that sounds silly but I see no other use for the spring. I have cleaned vents on different types of vehicles that were clogged and they did not have a spring under them.:wave:

 

[mtbtim]

If you take the breather apart you will find small spring under the cap but when you blow in it it does not unseat anything. So if you need to keep water out it's best to move it higher to keep all water out. My point is with the axle seal issues having positive pressure would only promote leakage. I did not design the vent but the spring may have been put there to stop it from rattling around I know that sounds silly but I see no other use for the spring. I have cleaned vents on different types of vehicles that were clogged and they did not have a spring under them.:wave:

Very interesting. My theory of how these breathers work wasn't accurate then. A spring with no apparent purpose. Who would have thunk? I think I have an old one laying around. I think I will tear it apart and take a look for myself. Thanks for sharing this.

 

[plcfcng]

great take it apart and let me know what you think about what I said above. Remember these are vents not check valves. hey your in the neighborhood. if your going to tim's ask him what he thinks