How to know if rear axle is original.

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So just bought 11 jk 108kml in September, and have been going through doing maintenance and researching everything. So we are planning on going to a offraod park this spring, and noticed something worry some. There doesn't seem to have every been an accident via Carfax, but the rear end and trans fluid was black, so I changed it. Then I noticed some chaulk writing on the rear axle. The back yard build side of me makes me think salvage yard axle. Which if it works and still is a Dana 44 then ok, but started thinking further. About gearing, I pulled the build sheet for my jk and it had 3.73 optional gearing, now I'm wandering if in is a different rear end, then if it is did they match off build sheet or just grab anything. Because what ive read says 3.21or 4.10 stock, so landing another 3.73 at a yard, not probable. Of course all of this is speculation, but I don't want to go in 4x4 and have 2 differ diffs, and burn up transfer case. But I also don't want to spend 600+ dollars on a guess. Is there any way to know?
 
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Is there any way to know what? Whether or not it's the original axle or what the gearing is?
If it's an identifiable Dana 44, the you have no worries other than was the swap done properly.
If the question is gearing, that's an easy one, too.

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And there's this video...

 
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Oh, ok that's what I didn't know, the stamp, I knew parts were serial stamped but didn't know was gear stamped. But in theory defence, that's the diff cover, if I switch to 4.56 gear unless I change the cover it will still say 3.73, right? Again I'm new jeep owner and been 2 kids since I've actually upgraded my vehicle. So excuse the question s been out the game for a minute.
 
Is there a mechanical way, like if it had an aftermarket cover with no I'd stamp?
The housing itself isn't stamped, it is a thin metal tag that is held on by the bolts. You definitely should get a new one to reflex the new gear ratio when it is changed. I would hope that new gearing kits come with the tag, because that makes sense, but I'm not sure that they do.
 
Is there a mechanical way, like if it had an aftermarket cover with no I'd stamp?
Yes, watch the YouTube video and he'll give you the other couple ways to do it:
- rotate wheel and count drive shaft rotations (1 complete rotation of the wheel = about 3.75 rotations of the driveshaft = 3.73)
- pull the diff cover and count teeth on the ring gear and divide by the number of teeth on the pinion (41/11= 3.73)
 
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So I got home finally and am installing some geo brackets and I looked where the tag is supposed to be on the diff, and nothing there, further more on the back side I found 110k in paint maker. So they got me on that one most likely based on what I'm seeing is a salvage yard axle. And probly trans to based on the matching fluids. I've had to do almost every maintenance that was suppose to be up to 100k since I got , one thing after another started failing. I'm gonna assume was a behind the camper jeep and left in gear when pulled, and not daily so no maintenance. But that's assumptions, could be any reason behind it. But definitely need to 100% verify that it has matching gears, before 4 wheeling
 
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