Differential Breather Valve leak

Hi all. My rear differential is leaking gear oil from underneath the flange on the breather valve. I swapped out the old valve for a new one. I have installed the new one with thread sealant and a nylon washer to try and form a seal. The gear oil is not over filled. The breather valve (OEM part from Toyota) is tight. Has anyone else had this problem? Driving me nuts.

 

How do you know the gear oil is not overfilled? Not trying to be a wise guy just that I want to hear how you checked it.

 

I looked into the oil fill hole and the gear oil is below the bottom edge. Actually, the gear oil looks a bit low. When I took off the fill nut there was a pressure release of air. Maybe the new breather valve I bought it faulty, or maybe the low gear oil level is producing more heat/pressure... I don't think that the breather flange is really designed as a seal - there is no crush washer and you have two very hard mating services which are not conducive to a seal. I don't think that the pressure is supposed to force oil up to the top of the axle. When I blow on the bottom of the new breather valve it will let some air past - but it is not easy to get air past it.

 

Sounds like the breather isn't breathing.

 

I think I will try a second breather valve....I will report back. If anyone has any other ideas let me know.j

 

Unfortunately the only way to truly tell is to drain and refill. Unless you know for sure where the level should be when you have put 3.8 Qts in it, It may not be where you think it should be.

 

Thanks guys for the feedback. I have drained it and am putting fresh oil in. We'll see what happens (I will repost and let you know).

 

Put fresh hydraulic oil in. Still leaking from under breather valve flange. Ordered a third breather valve, will arrive later this week. will let you know if that does the trick. If not, I am stumped.

 

Weird.

 

Fresh Hydraulic Fluid????? Should be 75W-90 synthetic gear oil. That is what you meant right???

 

Yes - sorry - 75w-90 synthetic gear oil, 3.8 quarts. Thanks for keeping me honest.

 

So - 2nd replacement breather valve, same result. Still leaking oil from under bolt flange. Anyone have any ideas? I am stumped.

 

No it's not, if you take off the fill plug and nothing comes out it's obviously not overfilled, which is what OP did.

OP can you take a photo of where it's leaking?

 

The breather just lets air pressure out when things heat up. Chances are when you removed the fill plug it wasn't under pressure but a vacuum. If oil is coming out the breather then either it's got to be getting thrown there by the rotating gears inside the diff or the oil is turning into a mist and as air escapes it's bring the oil mist with it. You could try a different brand of oil to see if that helps or you could do the breather mod (putting a rubber hose on the diff and moving the breather to a remote location in hopes any oil cools before it gets to the breather and runs back into the diff.

 

I don't think it has anything to do with the type of fluid. I bought the truck 2 months ago, shop changed the pinion seal, then the old breather valve started to leak. I put a new oem breather into the diff, still leaked. Put a crush washer under it and tightened it and put thread sealant on it - still leaked. Tried another new breather, still leaked. New dif fluid (synthetic 75W-90) still leaks. I don't think it is mist coming up with the air (leak seems to be from under the bolt flange) and it could only be leaking if internal pressure was pushing the oil up - otherwise it would not have gotten past the thread sealant.

 

Just throwing this out. Could one of the bearings be getting hot in the differential causing the vapor to come out the vent? Maybe shoot the back of the diff with a temp gun after driving for a bit.

When you changed the diff fluid did it look normal?

 

Agree with this. Do you know for sure it’s leaking at the threads instead of doing its job and too much fluid is “breathing” out? Maybe there is another issue going on.

 

I don't know if the diff fluid looked normal - it looked cloudy, but not overly dark. I don't know for sure it is coming up through the threads - could be coming up through the valve itself (in fact, perhaps that it more likely). It is likely heat related - on one short trip it did not leak - then later on a longer trip it did. I am not sure why it would be generating excess heat.

 

I would just put a hose nipple where the plug is, run 2ft of hose up to the bed/frame and then put the breather on the end of the hose. Common thing to extend the breather for water crossings, but it might "fix" your issue by just giving a couple feet for air to escape and not bubble shit out. Definitely weird. Usually when the breather gets clogged the axle seals get blown out. The diff getting hot idea is an interesting one too.

 

Thanks for all the ideas. I think the oil was bubbling out the breather valve, for reasons unknown to me. The differential is not noisy and while the metal is warm (not hot) after a long drive, I don't know if it is really getting super hot. I drove about 25 kms last night with this new set up and (touch wood) it didn't seem to leak at all. I used the union (part no:

$8 90404-51319 Toyota Union - 90404-51319

90404-51319) which I picked up from Toyota. I had the fuel line sitting around my shop and I hose clamped the breather valve to the other end so no water gets in the hose and zip tied it to the frame cross member, with slack to allow for suspension travel. Should not have had to do this - but there you go. I will post something if I have any more issues with the leak, or the differential generally.

 

I'm having a similar issue, I think. I'm wondering how this went for you. I'm gonna try and replace my breather valve first, and then go from there.

 

Anyone fine the cause of the issue. I have the breather mod and fluid is coming out of it.

 

Not sure how it went for everyone else, but I made the breather mod and I no longer have any diff fluid leaking.