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Old 06-22-2013, 01:40 PM   #1
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Knocking/ vibration noise in rear.

1995 2.5 YJ
To start... I have the 4 inch RC lift but drive shaft is still stock

So as I came home from work last night I noticed a knocking noise that would speed up in sound as I increased my speed. I have done a search on the forums and came across some one describing the same symptoms I have. Their issue turned out to be the center ball CV joint. Does this go by another name because I cant seem to find anything about how to remove it or even exactly where it is?

Ive got under the jeep and shook the drive shaft and there is a little play where the shaft goes into the diff. Its very minimal but it kind of makes the same noise as the knocking i get. Also while under there I noticed that im leaking diff fluid where the shaft goes in as well. Would low diff fluid cause a knocking noise?

Can anybody please point me in the right direction any help is greatly appreciated.

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Old 06-22-2013, 01:46 PM   #2
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Replace the U-Joint. Wouldn't be a bad idea to do all of them. Keep at least 1 extra in your tool/repair box for off road emergencies.

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Old 06-22-2013, 01:58 PM   #3
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Ah the U Joint. Yeah thats where I planned to start but I wanted to get all the details out in case it was something more than that.
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Old 06-22-2013, 02:07 PM   #4
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Ah the U Joint. Yeah thats where I planned to start but I wanted to get all the details out in case it was something more than that.
You dont have a center ball CV joint. The stock driveshaft just has a normal UJoint at each end. Get under your Jeep and try to shake each end of your driveshaft. Try to rotate it back and forth and move it around. The one with play in it is the bad one. Either it is that, or your rear differential is crapping out on you.
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Old 06-22-2013, 02:12 PM   #5
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Ok thanks guys, Im gonna go out and mess with it now. Hope its just the u joint.

Overkillyj, thanks for clearing up the centerball deal. I was reading about a tom woods shaft and thats where I got that from.
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Old 06-22-2013, 03:23 PM   #6
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Ok so there is no play in the U joints at all. The only play i get is from the shaft that goes into the rear diff. Im still going to replace the u joints since its pretty cheap.

Has anyone had any issue with the shaft going into the diff?
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Old 06-22-2013, 03:33 PM   #7
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Ok so there is no play in the U joints at all. The only play i get is from the shaft that goes into the rear diff. Im still going to replace the u joints since its pretty cheap.

Has anyone had any issue with the shaft going into the diff?
Yeah that is what I was talking about. That is your pinion. You probably will notcie that at some point recently you had oil seeping out right there and down the bottom of your diff housing. bet there is evidence of it even if your diff is too low to spew oil anymore. Pop the plug on the cover and stick your finger in there to see if you can feel how low the fluid is. If you cant feel it you have pretty big problems since it is supposed to be filled up to that hole. If that pinion has play in it, and I am talking about side to side/up and down play, NOT rotational play, (that would be backlash and a small amount is normal) then that means your pinion bearing is dead. If your pinion bearing is dead you do not have long until you are left somewhere with a dead Jeep. It costs a lot to have a pinion rebuilt and is not worth it in the Dana 35. If you have the money and skills get an 8.8 since they are cheap as hell and way stronger. If you are looking for a quick fix you would just want to pick up another Dana 35 with the same gear ratio since you could swap it in within about 2-3 hours max not having done it before.
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Old 06-22-2013, 03:33 PM   #8
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Does it happen the whole time your driving? Straight and turning? Did you shim or turn your rear axle towards the transfer case to lower your rear driveshaft angle?
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Old 06-22-2013, 04:11 PM   #9
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Btw from what you describe it does sound more like u joint than anything. Either problem whatever it is well happen a lot with your setup. You should address driveline angles once you fix your problem
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Old 06-22-2013, 04:14 PM   #10
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I popped the cap on the diff and there is fluid. Enough that it started seeping out of the hole. I do have the up and down + side to side play that you are talking about however it is very minimal. Is there a certain amount of play allowed or should it not budge at all?
It happens when Im accelerating and putting a load on it. It stops when i press in the clutch or just let off the gas. I do have the Tcase drop brackets that came with the RC kit but thats all.
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Old 06-22-2013, 04:16 PM   #11
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Yeah a SYE and drive shaft are on the list of to do's. Also the 8.8. Problem is that the money doesnt come in fast enough.
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Old 06-22-2013, 05:04 PM   #12
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Sounds more like a UJoint than anything. Look up some you tube videos on what to look for. Hard to describe.

And no, you should not have side to side or up and down play on your pinion. It should be solid in regards to that type of play. But if you dont have fluid seeping out of your pinion you should be fine. When the bearing starts to go the seal will go and you will see fluid.
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Old 06-22-2013, 05:21 PM   #13
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I do have fluid seeping out the front. I think its fair to say we found the problem. Im still going to change the u joint first, just to eliminate. Thanks for your time and help. Ill look into youtube now that i have an idea of what to look for.
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Old 06-22-2013, 05:33 PM   #14
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I found this short video. Mine is moving in the same area but while his is moving, lets say 1/4 of an inch, mine is moving way way less, like 1/16 of an inch, if that. The play in mine is almost not noticable compared to this. Are we still talking the same thing? Also mine does not move in and out


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Old 06-22-2013, 06:24 PM   #15
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I do have fluid seeping out the front. I think its fair to say we found the problem. Im still going to change the u joint first, just to eliminate. Thanks for your time and help. Ill look into youtube now that i have an idea of what to look for.
Just because fluid is leaking does not mean it is bad. I destroy my seals once a year and have to replace them. They are cheap and easy. Also, it is your rear causing the problem, not the front. Since you said it happens under power that eliminates the front. Unless you are driving around in 4X4.
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Old 06-22-2013, 07:40 PM   #16
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No I didnt mean the front as the front diff, I meant its leaking out of the front of the rear diff. I went and got a u joint but its raining pretty hard right now so ill try it tomorrow.
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Old 06-22-2013, 07:43 PM   #17
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No I didnt mean the front as the front diff, I meant its leaking out of the front of the rear diff. I went and got a u joint but its raining pretty hard right now so ill try it tomorrow.
That sucks man. You have some troubleshooting to do. Put the rear on Jackstands, and put it in drive. That is the easiest way to figure out if your rear is going. Hopefully for your sake is a ujoint. Otherwise 8.8 it!

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