Mitsubishi Challenger Differential

Submitted: Saturday, Apr 26, 2014 at 15:40
ThreadID: 107472 Views:2518 Replies:5 FollowUps:9
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When removing the filler plug from the diff there is a noise like opening a soft drink bottle, eg a gassy sound. Has anybody had this problem and what is causing it please.

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Reply By: Member - Phil G (SA) - Saturday, Apr 26, 2014 at 15:45

Saturday, Apr 26, 2014 at 15:45
Its normal. It a bit of air rushing in. The air in the diff expands when hot and contracts when cold. It tells you that your seals are working perfectly!
AnswerID: 531265

Reply By: Bigfish - Saturday, Apr 26, 2014 at 16:32

Saturday, Apr 26, 2014 at 16:32
Exactly what Phil said...
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Reply By: blown4by - Saturday, Apr 26, 2014 at 18:06

Saturday, Apr 26, 2014 at 18:06
Yes it is a sign your seals are working but more importantly it is also a sure sign your diff breather is blocked. As has been said when the diff gets hot the air inside expands and has to be able to escape to equalise the pressure with atmosphere otherwise the pressure build up would blow diff oil past the seals. Also when the diff cools down the air contracts and if weren't for a functioning breather air would have to be forced in to the diff by the higher atmospheric pressure outside the diff. It is particularly important to have the breather functioning when you do a water crossing otherwise the hot diff will suffer water ingress past the seals when the air inside the diff cools rapidly upon entering the water. The breather is probably blocked with mud, dirt, dust, wasp nest, etc. Look for a small tube or hose from the top of the diff or diff housing going up to a high point under the car. Remove it, clean it, blow through it and re-fit the line and you troubles will evaporate. Same applies to the front diff and gearbox/transmission.
AnswerID: 531272

Follow Up By: Member - Phil G (SA) - Saturday, Apr 26, 2014 at 20:51

Saturday, Apr 26, 2014 at 20:51
Not blocked. The factory breathers have a one way valve held closed by a small spring, so they open when pressure builds up, but shut to stop water/dust entering through the breather.
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Follow Up By: Ross M - Saturday, Apr 26, 2014 at 21:09

Saturday, Apr 26, 2014 at 21:09
That is a really good idea so the water depth head pressure, the cooling action of water ie vacuum and the resulting negative pressure can readily draw in water to wheel bearings or diff pinion seals. Sounds like fun.

Sounds like a dubious advancement in technology to me.
That situation can't be any good for anything but a town only car and event then no good if floods in town happen either.

If it was made properly as a 4wd should be then it won't try and take water in.

If going near water it will be best to change it so it breathes as they should with decent breather tubes to high areas in the vehicle.
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FollowupID: 814285

Follow Up By: Member - Phil G (SA) - Saturday, Apr 26, 2014 at 21:11

Saturday, Apr 26, 2014 at 21:11
Gday Ross,
Well Toyota (and others) have made them way for at least the last 30 years. See my photo below
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FollowupID: 814287

Reply By: Ross M - Saturday, Apr 26, 2014 at 18:37

Saturday, Apr 26, 2014 at 18:37
If there is any puff OUT, or IN, the breather is blocked and needs to be checked. That is why they have breathers, so they can "breathe". Ie pressure equalization with outside.

There should be no noise as you described and if I ever hear any, I check the breather hose for being clear AND also check the fitting which attaches to the axle housing.
It is usually a small dia hole in the fitting and dried oil scum. especially if a diff additive is used will dry in there and cause a blockage.
If any pressure builds up, the pinion seal is the high speed seal which will be stressed with higher lip loading than normal and it will just wear away.
Landcruisers will do a seal in 200km easily because they are faster than the wheel seals, but the wheel seals are also suffering and thier life shortened considerably.

If thee has been pressure and it gradually escapes AND the seal lips then holds a vacuum, when crossing rivers etc, the sudden cool will increase the vacuum and surely suck in water.

Having a breather is the best way to stop it all happening, Therefore, there must be NO FFFTT when you open the filler.

So, sorry, I can't agree with anyone who says it is normal or ok.
AnswerID: 531276

Follow Up By: Member - Phil G (SA) - Saturday, Apr 26, 2014 at 21:09

Saturday, Apr 26, 2014 at 21:09
Hi Ross,
There's a first for everything!
It is a valve. I suggest you take one off and blow into it then try to suck on it...avoid a mouth full of diff oil if you can!
You'll see from the photo below - top breather is the assembled factory breather and the bottom one is disassembled showing the spring and seal and cap. And yes, its normal for a slight sucking sound when you break the seal as you undo the filler nut. Cheers Phil
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Follow Up By: Bob R4 - Saturday, Apr 26, 2014 at 21:30

Saturday, Apr 26, 2014 at 21:30
Geez Phil, you spoilt this discussion in a hurry with the facts!
Bob
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Follow Up By: Member - Phil G (SA) - Saturday, Apr 26, 2014 at 21:41

Saturday, Apr 26, 2014 at 21:41
The footy was getting boring, so my threshold for going out to the shed and pulling one apart was not great.
Its pretty rare to catch Ross out.....he usually keeps me honest :-)
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FollowupID: 814291

Follow Up By: Ross M - Saturday, Apr 26, 2014 at 21:44

Saturday, Apr 26, 2014 at 21:44
Lovely picture Phil.
I understand what it does.
Still doesn't alter the fact it will cause any seal to try and suck in water in many situations.

I suppose you could call it a "quick dunk only valve" because it holds the vacuum of cooling and facilitates the ingress of water.
During a river crossing of only a small depth water will be invited onboard.

All depends on the level of protection you think is OK I suppose.
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FollowupID: 814292

Follow Up By: Member - Phil G (SA) - Saturday, Apr 26, 2014 at 22:02

Saturday, Apr 26, 2014 at 22:02
It depends on how much negative pressure is generated when a diff plunges into cold water and how good/bad the axle seals are.
I think the problem is overstated and is only a problem on old and poorly maintained vehicles with worn seals.
I've always extended the diff breathers in the past, but on this new vehicle I won't bother.
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Reply By: Bigfish - Sunday, Apr 27, 2014 at 07:21

Sunday, Apr 27, 2014 at 07:21
Exactly Phil...Ross is wrong but too bloody minded to admit it. Seals can take a fair amount of pressure and as you say Toyota have been doing it this this way for decades. The valve is simple and efficient and WORKS...
AnswerID: 531306

Follow Up By: Ross M - Sunday, Apr 27, 2014 at 08:58

Sunday, Apr 27, 2014 at 08:58
Bigfish
Seals aren't really designed to take positive or negative pressure at all.
If subjected to it for long they DO wear out the seal lips, then they suck in water if it is present at the seal lip.

Being poorly maintained as Phil mentioned means the seal which isn't leaking yet, although worn a bit, has to be changed long before it's service life. Most people don't keep on changing seals just because it might be worn, they usually leave it until they a show signs of requiring replacement.
Therefore they will then suck in water if present. If you aren't going in water, then you don't even need the spring or valve either.

Just the way it is.

If you ever have to stop or cross a wide river you don't want that valve helping to drag in water. OK for Mr. and Mrs Average though.
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FollowupID: 814312

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