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Unread 12-02-2010, 03:21 PM   #1
RugbyNimbus
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2000 TJ Wrangler 
 
Join Date: Dec 2010
Location: Kansas City, MO
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DIAGNOSIS HELP: TJ Rear - Bump & Grind

Let me start by saying, I'm handy and can fumble my way around repairs via a Chilton/Haynes manual, but I'm not a mechanic, so please -- go easy on me.

I have a used (125k) TJ, 5 spd, that I've owned for all of four months. I have limited (and likely bogus) info on previous owners via the lot that I got it from; for what little it's worth, the CarFax I ran came up clean. No real mechanical issues to date outside of a lingering whine when pressing in the clutch, as if something was slowly rolling to a stop, but no problems or resistance to gear shifts ... I've been guessing it's the throw-out bearing going bad.

So today, a cold morning, I get in, head out, and halfway up a moderate hill in our subdivision (but moderate RPMs), I hear a loud "clunk" from underneath the body, followed by rhythmic grinding that sounds like it's coming from the back end.

* The pattern of it is roughly a slow "cuh-cuh-CLACK, cuh-cuh-CLACK" that parallels the speed.

* Other than the terrible noise (that goes right through the frame and into the pit of my soul), it drives/accelerates/rides "normally".

* Engaging 4wd hi/low, clutch in/out, forward vs. reverse -- none of it makes any difference.

* However, turning to the point where the body leans (esp. to the left) quiets it up briefly.

My suspicion: The rear differential just died, and if I open it, I'll find the metal-shaving equivalent of used coffee grounds. Lovely.

Worth noting: A quick inspection of the rear diff. revealed some grease-pencil writing on it (so prob. replaced/rebuilt recently?) and while the lube level was low, I was more disturbed by the brown-sludge appearance of it.

Before I throw any money at this problem, any thoughts, suggestions or been-there-myself insights? Thanks!

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Unread 12-02-2010, 03:54 PM   #2
Osboy1
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Join Date: Apr 2010
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Quote:
Originally Posted by RugbyNimbus View Post
... I was more disturbed by the brown-sludge appearance of it.
Like dirty engine oil brown, or like a nasty chocolate milkshake brown? If the latter, there's water in the gear oil. Is the breather tube still attached?
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Unread 12-02-2010, 06:03 PM   #3
RugbyNimbus
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Join Date: Dec 2010
Location: Kansas City, MO
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Thanks for the response. It's more the latter -- an almost frothy texture. I thought the "glistening" was from metal fragments (actually none to be found...yet), but when I wiped some of the lubricant onto a newspaper and it sat for a while, it settled into just dirty oil. So the glitter was actually bubbles, and lots of them. Could be water doing it.

I have a car-nut neighbor who's going to help me get it up on some jacks and listen underneath with wheels in motion to better pinpoint the source of the noise, but that won't be for another week or so. After we ran it up and down the driveway briefly, he's split 50/50 between rear diff. or transfer case.
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Unread 12-02-2010, 06:04 PM   #4
RugbyNimbus
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Oh, and I'll check for the breather tube and get back to you.
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Unread 12-08-2010, 05:10 PM   #5
RugbyNimbus
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Join Date: Dec 2010
Location: Kansas City, MO
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Got it up on jacks this afternoon and the noise is definitely coming from the rear differential. So that'll get opened up and likely the ring/pinion gears will need replaced.

I have two questions before I start:

1). The diff. cover has a date stamp that pre-dates the Jeep ('97 on a '00 vehicle), and recent grease-pencil ("3.73") written on it. Since I changed the tires to 31" after buying it, would the new tire diameter not playing nice with a 3.73 gearing ratio be the likely cause of the diff. failure?

2.) Since I'm going to likely be replacing parts anyway, I have the opportunity to upgrade the differential parts. Any suggestions on where to look for new bits (e.g., "find a Rubicon at a junkyard", order from JCWhitney, etc etc.) ...and if 3.73 is even the right ratio for me (I have 31" tires for now, eventually going to 33s, mostly street driving with occasional moderate off-roading/mud/snow)?

Thanks in advance to any who care to chime in with info!

Last edited by RugbyNimbus; 12-08-2010 at 05:13 PM.. Reason: typos
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Unread 12-08-2010, 05:49 PM   #6
RugbyNimbus
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2000 TJ Wrangler 
 
Join Date: Dec 2010
Location: Kansas City, MO
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Spending a little while reviewing other Jeep forums -- you know, the ones with better search functions -- I've learned a lot about Dana axles, so just ignore my first question about the gearing. But I'm still curious about the answers/experiences people have with the second one.
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axle , differential , grinding noise , transfer case

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