Pressure in rear diff?

[vicpick58]

I was working on my 100,000 mile service today and changed the lube in the rear differential, when I removed the upper plug, there was hissing of pressurized air from inside the pumpkin.

I noticed this a little the last time I changed the lubricant at 50k miles too. But this time there seemed to be quite a bit of pressure.

I just wonder is this normal for a Toyota? and what about blowing the wheel seals of the axle?


Oh, by the way I did this gear oil change with the diff stone cold. Maybe that had something to do with it, normally I do it while warm.

 

[Jeremy556]

The stock breather is a one way valve, which will allow pressure out when the diff is hot. When it is cold, it will be at negative pressure, hence the danger of sucking water past seals, and the reason for relocating the diff breather and leaving it open, instead of 1 way.

 

[Saker]

The stock breather is a one way valve, which will allow pressure out when the diff is hot. When it is cold, it will be at negative pressure, hence the danger of sucking water past seals, and the reason for relocating the diff breather and leaving it open, instead of 1 way.

Here is a link to what Jeremy referring: "Scuba Mod" or Rear Diff Breather Mod - Complete!

 

[vicpick58]

Thanks for the info, I had seen the vent relocation post title, but thought that since I do not really use my rig for off road, and don't drive in deep water, it did not apply to me.

However if there really can be negative pressure in the diff, I can see that one only needs to get up to a wheel hub in water to suck past a seal, not just water deep enough to get in the vent.

I guess I will be working on this mod in the near future. At least up till now I have not had any trouble with it and the lube that drained out was nearly as clean as the new stuff going in. No milky colored stuff indicating water in the diff.

With 100k miles on my vehicle now, I am sure the seals are not as good as new anymore and better chance of the vacuum actually causing them to start leaking sooner than necessary.

 

[wfo9]

Like he said, you most likely heard air going in not air going out.

I really don't think the concern with water getting past the seals is something to worry about if you don't do water crossings, or run an air locker....

My truck has seen a few minor water crossings and had no issues at all with the diff fluid. However, I did recently add the two way breather when I added an air locker.

It's not hard to do at all, just don't think most people need to worry about it.

 

[fourwd1]

Occasionally the breather can get clogged or pinched, and the pressure needs to find another way out, and that's usually past the pinion seal.

 

[wfo9]

Occasionally the breather can get clogged or pinched, and the pressure needs to find another way out, and that's usually past the pinion seal.

With the stock setup there is nothing to get pinched and almost no way for it to get clogged. However, there is also no easy way for air to get in, only out.