Dirty Front Differential Oil


andy29847

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My jeep is a 2004 Rubicon. I've had it ~4 years. I did fluid changes all around when I bought the Jeep. Since then, for various reasons, I've changed the oil 2 more times. Each time, the front differential oil is dirtier than the rear. Yesterday, I pulled the differential cover to look inside. Everything I saw looked OK, but I couldn't really see the internals of the locker. The inside of the housing and gears was coated with a black residue. The magnetic plugs had some goop on them, more than I would expect given the oil changes I have made. The front has had some significant use in the past 2 months. Lots of low range and some locker action. Operation has been trouble free except for a thumping noise I get occasionally at full steering lock (axle not locked). When I first heard this noise, I thought it might be the front axle u-joints binding a full lock. That is not what it is. I believe the noise is coming from the axle locker mechanism. Maybe the locker isn't full disengaging at times. I cleaned everything inside the housing with brake cleaner and put in some new oil. Maybe the cleaning will make the difference. I'd like to hear your thoughts and experiences with similar problems.
 

Westtown Willy

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That’s interesting, I’m curious to hear other’s opinions. I change my diff oil front & rear every summer & the rear is nasty and black while the front looks like it’s pouring out of a new bottle and that’s been with a ton of off road use. As a result this year I only did the rear, tired of wasting the time/money on the front. I may check it next year to be sure, though I’ve largely stopped going off road so I’m not sure I’ll need to change it anytime soon. Something certainly sounds off with yours but I don't know.
 

Irun

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A couple years ago I had an issue with my rear locker not dis-engaging. Interestingly, it turned out there were two things going on simultaneously. First, my rear locker pump was pumping air fine, but wouldn't bleed of air. Eventually it would clear itself, but stayed partially engaged long enough that I heard and felt it.

Second, after replacing the pump, the rear still stayed engaged after the pump was shut off. It wasn't as bad as before, but the problem was still there. After taking the rear cover off I found the differential itself was incredibly dirty. I thoroughly cleaned it, like you described. When I refilled it, I did so with synthetic instead of conventional gear oil. After running it like that for a few days I drained the still dirty synthetic oil and switched back to conventional oil. Since then I haven't had any issues.

I can't really offer anything about the front or rear being dirtier, because I've run lockout hubs on the front for the last 7+ years.
 
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pagrey

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Personally I'd change it more often if it looked bad. What mileage are you running on a change? I'm not saying you are doing this but I have friends that tell me they did something a few times in the last few years and when they check the paperwork it always seems to be allot worse than they remembered. The rear probably looks clean because it gets hot enough to burn off crap through the breather when you drive. The front rarely generates enough heat to cook off garbage. You might double check the front breather too just to make sure it's properly vented.
 
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andy29847

andy29847

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That’s interesting, I’m curious to hear other’s opinions. I change my diff oil front & rear every summer & the rear is nasty and black while the front looks like it’s pouring out of a new bottle and that’s been with a ton of off road use.
Exactly the opposite of my issue. :) I changed the front diff oil when I got the Jeep (1). I changed it again 18 months later after I removed and replaced the axles. I changed it again ~ 2 years later, just before my recent trip. I changed it again 7 weeks later (yesterday) after I returned home from my trip. The back has only been changed twice. The back looked good as new both times. FWIW, testing after yesterday's cleaning and oil change found the lockers working as expected and no thumping noises from under the Jeep. Checking the breather is a good idea. I'll do that soon.