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Discussion Starter #1 (Edited)
I changed the rear diff fluid a couple of weeks ago on a scheduled basis. I was stunned by its color. It was something between the "coffee-and-milk", an old oil from the fryer and - sorry - children's diarrhea. Everything inside the diff housing was covered with reddish scurf but details were not rusty. I just wiped them off with a piece of cloth and they became shiny again.

I continue... Along with the "oil" I found some unidentified pieces of black rubber (???) inside the diff's housing. I decided it was the sealant's excess but I never seen the stuff inside the diff before.

My first thought was I somehow killed the vari-lock and the "oil" looks so strange due to worn clutch inside of varilok. But I didn't check that. Just removed the gunk and changed the oil.

It has been 2 weeks from the oil change. The truck passed ~500km, no off-road, no fords, nothing. Today I pulled the plug out of the differential cover and what do you think? I can see almost the same milky "oil" inside the diff (well, maybe not so milky as the previous time...). The diff's breather is ok, oil seals are ok too, so I don't think it's water.

What else it might be if not the water? Should I buy new varilok - 52104674AE? Or change the make of my oil (which is Castrol Syntrax Limited Slip 75W-140)

Any feedback would be highly appreciated.
 

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Discussion Starter #5 (Edited)
It does sound a lot like water. Maybe there could be some residual water from the previous oil change. Had the Commander been through some deeper water previously?
No it had not. Maybe some shallow puddles, no more. The irony is what these 8 months were the most "peaceful season" for Commander from the moment when I bought it. I missed winter hunt in snows above its front bumber, I almost missed the spring hunt with its river floods. So I just don't understand where the diff could get the water.

My only reasonable suggestion is that the breather has been frozen throughout the winter and differential has taken water from the air (from my knowledge, the oil seals' purpose is to hold the oil, but they allow some air to get inside) and the water just couldn't vapourise through the breather. The more I drove the more water vapor appeared inside the housing. But if so, why I haven't seen any rust?

I'm gonna check rear diff after next 200 miles and hope to not see the horror again, but if so... :(
 

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No no it's ok. The breather is "like new".
When I last replaced the diff fluid I was surprised to find that if you spin one of the tires, a lot of additional fluid drains out. I had already drained the diff and was just curious about the way the gears mesh, so I spun one tire with my foot. Much to my surprise a fair amount of old diff fluid started to drain out. I spun the tire until no more fluid came out and then resealed the diff and refilled it. Maybe what clouded the fresh fluid you put in was this residual old fluid.
 

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Discussion Starter #8
When I last replaced the diff fluid I was surprised to find that if you spin one of the tires, a lot of additional fluid drains out.
Every time I replace the oil I spin the wheels exactly to drain out as much old stuff as possible. That's why I believe the old oil residues could not spoil the new one.
 

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Clean it out really good with brake cleaner an install new gear oil and you will be fine. The brake cleaner won't hurt anything but will clean it up really nice.
 

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Discussion Starter #10
Clean it out really good with brake cleaner
Sure, you right, it should help. But it didn't. Every time I replace oil, I spend a full can (340ml ~ 11.5 oz) of such cleaner for every axis and I did that the last time (when I found out the oil is bad for the first time).

I admit, that oil might be milky before the second change due to residues from the previous one. But what I can't understand is how the water got into the diff housing, and is that the water at all.

If this weekend I find the oil is spoiled again, I'll try to extract water from the mixture. If to heat up the oil-water mixture I can see a foam. Don't know why I didn't do that yet.
 

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Discussion Starter #12
Not sure what do you mean. My axle has the only breather, on its right side. Which other vent tubes I overlooked?
 

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At the 200km mark change it again (maybe put some cheaper oil in) and check it again after another 200 km.
Since it sounds like you use or commander off road it would be better to extend the breather lines to a higher spot under the hood.
 

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Discussion Starter #15
Hope so, however can't understand - how. The alternative (to change varilok) is horrible for me
 

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Discussion Starter #16
At the 200km mark change it again (maybe put some cheaper oil in) and check it again after another 200 km.
Since it sounds like you use or commander off road it would be better to extend the breather lines to a higher spot under the hood.
This Saturday will show what do I have there.... Next winter I plan to go North, so I will extend lines, insulate fuel pipes etc
 

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Discussion Starter #17
Well, it's Saturday and I'm reporting what the rear diff's oil is significally darker than the fresh one, right after the truck stop it contained some tiny air bubbles. It's not milky anymore.

So, I don't know what was that. I think some of you're right, it was the water. But I don't have any ideas on how is that possible.

Anyway, thanks for participation in the discussion.
 

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Discussion Starter #18
Well I am back again with the same problem. What's the difference is that I know the answer.

A few days ago I've been performing a scheduled maintenance during which I checked the rear axle's oil. The oil was reddish again, despite its change just 1000 miles ago. It's not the water itself, but the aftermath of its presence inside the... ta-da! .. breather. The source of the problem became obvious when I disconnected the breather's hose. The very end of breather was not not only rusty, the breather itself has been clogged. What I did next is what I should have done before the epopee has started.

1. Clear the breather's hose from inside. It was clean and ok (as I told)
2. I broke the cloggage with a wire and flushed the axle with gunk cleaner. When draining, I've seen a lot of rust and particles of sealant (so the source of the problem is excess of sealant that tore itself away from the edge of the cover and clogged the breather hole. So, don't overlube the cover when sealing it)
3. Total amount of cleaner fluid I used for the axle was almost a litre. ~2 quarts
4. Sealed, added oil (2 litres of castrol syntrax limited slip 75w-140) and made 200 kms for a few hours. I noted that axle start to howl at 70 mph.
5. I Stopped the truck and extracted the diff's plug and checked oil. It was like a new with a small amount of air bubbles but with no traces of the rust. I was surprised that oil level was significally below the edge of the filling hole, but I couldn't find any signs of oil leakage . I added some more oil and
now it's ok.

Hope never to return to the thread )
 
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