Noise in rear differential - JeepForum.com
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post #1 of 20 Old 07-24-2013, 03:58 PM Thread Starter
sidehillbill
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Noise in rear differential

Good evening Jeep experts. I bought a 79 CJ 7 last week, 6 cyl, auto, Quadratrac. When I got it home and started going through it more I discovered that the light on in the gauge cluster is actually the light for emergency drive, not the brake warning light that I thought it was at first.

I did some reading and looking on here and learned how Quadratrac works, found the glove box and selector switch in a box of parts, the hoses to the switch and transfer case are gone, no big deal, I can fix that.

I got under the Jeep with a vacuum pump and tried the actuator, it works both ways, so now I have it in normal drive and am getting a snapping noise that I didn't notice before in the rear diff when turning sharply or under hard acceleration.

I jacked the rear up and in park rotated one wheel and watched the other, it turned in the opposite direction, ah, open diff says I. So then I tried a hard takeoff or two on dirt and grass both and cannot get any wheel spin just pulls hard with the snapping and a bit of a shudder.

What kind of mess have I got into? Is it a limited slip diff? Sorry, I don't know for sure which axle it is, does anyone have an id chart?

Sorry for the long post, just wanted to provide as much info as I could.

Thanks for reading and for any help.

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post #2 of 20 Old 07-24-2013, 04:12 PM
OrangeCJ-5
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Not sure but maybe a broken tooth or two? Won't know until you pull the diff cover...
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post #3 of 20 Old 07-24-2013, 04:23 PM
jeepdaddy2000
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One of three things:
Either the LS in the T case is juttering or the chain is lose and ratcheting. I tend to discount the chain since it didn't do it with the E drive engaged. I suggest you drain the t case and refill it with either the recomended fluid or a mix of 90WT and friction additive.
Or you have a stripped hub on one of the two piece rear axles. Running the t case in E drive eased the strain on the hub, keeping it from spinning.
Mark the nut and the hub on both sides.
Power the Jeep till you hear the noise.
Check to see if the marks are still aligned.
If all else fails, drip the diff lid and inspect the diff. You may have a trac lok that has gone bad.
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post #4 of 20 Old 07-24-2013, 05:18 PM Thread Starter
sidehillbill
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Good stuff there jeepdaddy. Are those rear hubs splined or are they tapered like the old Mopar axles?
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post #5 of 20 Old 07-24-2013, 10:47 PM
Joe6Pack74
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If it was a Richmond Lockright locker it would click going into a turn but on jackstands it would turn both wheels in same direction. One way to find out is remove the diff cover and look. Diff gasket is not expensive.
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post #6 of 20 Old 07-25-2013, 02:05 AM
keith460
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Quote:
Originally Posted by sidehillbill View Post
Good stuff there jeepdaddy. Are those rear hubs splined or are they tapered like the old Mopar axles?
Both.

The hub has tapered splines inside that are cut and formed by the tapered splines on the shaft as it is mounted. There is a "woodruff" key also nestled on the shaft and hub.

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post #7 of 20 Old 07-25-2013, 04:35 AM
jeepdaddy2000
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Quote:
Originally Posted by sidehillbill View Post
Good stuff there jeepdaddy. Are those rear hubs splined or are they tapered like the old Mopar axles?
Early D44's used a large, smooth taper with a hefty woodruff key. The model 20's found in later CJ's (and most AMC/Rambler cars) used a small tapered shaft end with tiny splines and a very small key. While it is next to impossible to spin the 44, loosing a hub on the 20 is a common occurrence.
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post #8 of 20 Old 07-25-2013, 12:21 PM
82JeepCJ7
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If you spin a two piece hub/axle, the woodruff key is a very effective cutting tool and will systematically destroy said hub and shaft.

Beat it to fit, paint it to match!

Wheel, Wrench, Repeat.
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post #9 of 20 Old 07-25-2013, 04:20 PM Thread Starter
sidehillbill
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Quote:
Originally Posted by jeepdaddy2000 View Post
Early D44's used a large, smooth taper with a hefty woodruff key. The model 20's found in later CJ's (and most AMC/Rambler cars) used a small tapered shaft end with tiny splines and a very small key. While it is next to impossible to spin the 44, loosing a hub on the 20 is a common occurrence.

I have to believe this is a D 44 due to the fact that the pot is a lot bigger than the one in my 85 4 cyl. plow Jeep. I would love to find an axle id chart for these Jeeps.

I haven't had time to do any more checking, I'll get back with what I find.

Thanks for everybody's input.
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post #10 of 20 Old 07-25-2013, 04:26 PM
skizriz
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The quadrac option never came with a 44. If it is one, it was swapped in. Id be checking for proper gear ratio.

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78 CJ7.. 258.. TH400/Dana18.. SOA/stock YJ springs.. 35" General Grabbers.. Waggy 44s.. 4.88 gears...Spartan/Lockright...Fiberglass front to rear
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post #11 of 20 Old 07-26-2013, 06:35 AM Thread Starter
sidehillbill
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Quote:
Originally Posted by skizriz View Post
The quadrac option never came with a 44. If it is one, it was swapped in. Id be checking for proper gear ratio.

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Good to know. After searching this fine site I found this.

http://www.jeepforum.com/forum/attac...tion-chart.gif


Looks like I have the AMC 20 axle.
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post #12 of 20 Old 07-26-2013, 05:15 PM
skizriz
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The AMC 20 for a Q-trac is pretty easy to identify. They also have the offset pumpkin to the passenger's side. It should have (possibly only gears they came with) 3.54 gearing.

Here's a set I picked up last week for mine.


Here's what the stock two piece axles will look like. Under the dust cover, there is a large nut that holds the hub on.


I would be surprised if it was a spun hub. With the full time 4x4 splitting power to both front and rear axles, I doubt if it would create the torque to do it. Possible, but doubtful.

A slipping Q-trac chain would feel like major thumping right under your feet. Enough for you to feel in your soles under hard acceleration.

Seeing as you just bought it, it would be a good idea to open both diffs. Check the ratios, and change the oil.

Also drain and change the Q-trac oil in the t-case. You never know what the PO put in it, and the wrong oil will ruin it. Mine got trashed from the PO running ATF in it.

78 CJ7.. 258.. TH400/Dana18.. SOA/stock YJ springs.. 35" General Grabbers.. Waggy 44s.. 4.88 gears...Spartan/Lockright...Fiberglass front to rear
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post #13 of 20 Old 07-29-2013, 01:19 PM Thread Starter
sidehillbill
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Okay, after a bit more driving I tend to think the noise is actually in the transfer case as has been suggested. I haven't had a chance to check anything physically as I have spent the last few days dealing with metal fragments in my eye, yes I was wearing safety glasses.

I'm trying to find a source for the proper transfer case fluid, jeepdaddy said a mix of 90w and friction additive will work, does any one know the mix ratio?

Thanks again.
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post #14 of 20 Old 07-29-2013, 01:27 PM
LumpyGrits
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Dana 300 t'case uses std. 90w gear oil.
When was the last time you checked the oil level?
LG
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post #15 of 20 Old 07-29-2013, 01:34 PM
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Quote:
Originally Posted by LumpyGrits View Post
Dana 300 t'case uses std. 90w gear oil.
When was the last time you checked the oil level?
LG
It sure does......but the OP's is a QT.

'84 CJ-7: Yota axles (spartan locked front, e-locked rear) 4" BDS, 1" Daystar & 3/8" shackle lifts, 35" X-Terrains on steelies, YJ Tub & family roll bar, heater blower upgrade, 4.2L w/MC2100 & Team Rush, Warn 8274. Rebuilt 4.2/4.0 hybrid, AX15 and twin sticks/clocking ring waiting to go in.

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