Hissing when opening diff fluid bolt

Hello

As advised in the maintenance schedule I check my differential fluid level. It was fine, I almost feel it was a waste of two good crush washers. But my question isn't about that.

When I slowly undid the bolt on the rear diff - it made a hissing noise, like air rushing in our out. So I'm curious if anyone has thoughts on that.

Is it better if there's positive or negative air pressure in there? I can sort of control that by choosing what time of the year I open it.

Does it perhaps not matter at all that there's a pressure difference between the inside and the outside of the differential?

Thanks for any thoughts you have on the topic.

 

Check the breather cap. Give it a few twirls, it may be clogged

 

Where's that? I don't see it in the manual.

 

Should be on top of the diff

 

Is it possible that it's there but they didn't put it in the diagram?

 

Form my 2017 Limited, Part #90930-A3001 appllicable through 2020 model year. Maybe you don't have one on your 2021....hence, the hiss.

 

I think the hissing sound is normal.

the breather valve is a one way out valve to allow expanded air (from heat) to exit. it's also one way to block dirt and water from getting inside the rear diff.
When the rear diff fluid gets cold (air contracts), and since the valve is one way (out) and is working properly, there will be less pressure inside the rear diff and when you remove the plug, the air goes in (due to pressure differential) and it can make a hissing sound depending on how hot or cold the rear diff temperature is.

 

Think this is the appropriate diagram. Believe the 2021 Seqouoa is independent rear suspension? Rear breather appears to be part number 41108C. Could be hissing from too much pressure inside, or as previously stated, breather is one way, could be hissing (normally) due to lower pressure inside when it cools.

 

Sorry for the hijack, but do you have the torque specs for the 41101E bolts? I am curious if mine are under-torqued from the factory. I posted about my differential weeping in this thread:

https://www.tundras.com/threads/weeping-rear-diff.106465/#post-2741486

If you have the full service manual from which this diagram came from I would be grateful if you could share .

I also see 2 diagrams in this post so just to be certain I have a 2021 Tundra.

 

You can’t just say “with all due respect” and hijack someone else’s thread.

 

Fair and well received. Been scouring for information, however, I should have reserved this for a PM or a separate post. Sorry, all.

 

Thanks guys, that makes sense!