Knocking sound seems to come from front differential only in 2WD - Jeep Wrangler Forum
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Old 02-12-2014, 09:09 AM   #1
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Knocking sound seems to come from front differential only in 2WD

Hey all,

My '94 YJ Wrangler has recently started making this strange knocking sound. It seems to be coming from the front differential and sounds like it's coming from the passenger side but it's impossible to tell when driving. I can hear it from the drivers side when the window's down too. It only happens in 2WD. The instant 4WD is engaged, HI or LOW, it stops. I have replaced the U-joint on the drivers side axle because it was completely shot and rattling constantly. It sounded like loose washers rattling. The seals had completely rusted out and most of the pin bearings were powerized. I could move it side to side in all directions. Anyway, the U-joint on the passenger side seems fine. It's not loose and looks good visually. I've looked at the both drive shafts and neither seems to have any play in the U-joints but that wouldn't make sense to me anyway. If it was the rear drive shaft it wouldn't matter if it was in 4WD or not, it would make noise any time the Jeep was in motion, and if it was the front, wouldn't it make more noise in 4WD i.e. under load? I was thinking it might have something to do with the silly 4WD vacuum motor and fork on the passenger side of the front differential. It kind of sounds like a rubbing sound like a bearing, like metal scraping an unevenly worn or rusted surface...not like a hard knocking sound like an engine knock or a pop from suspension or steering components. Anyone have any ideas or experience?

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Old 02-12-2014, 09:42 AM   #2
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Originally Posted by Radioactiveman View Post
Hey all,

My '94 YJ Wrangler has recently started making this strange knocking sound. It seems to be coming from the front differential and sounds like it's coming from the passenger side but it's impossible to tell when driving. I can hear it from the drivers side when the window's down too. It only happens in 2WD. The instant 4WD is engaged, HI or LOW, it stops. I have replaced the U-joint on the drivers side axle because it was completely shot and rattling constantly. It sounded like loose washers rattling. The seals had completely rusted out and most of the pin bearings were powerized. I could move it side to side in all directions. Anyway, the U-joint on the passenger side seems fine. It's not loose and looks good visually. I've looked at the both drive shafts and neither seems to have any play in the U-joints but that wouldn't make sense to me anyway. If it was the rear drive shaft it wouldn't matter if it was in 4WD or not, it would make noise any time the Jeep was in motion, and if it was the front, wouldn't it make more noise in 4WD i.e. under load? I was thinking it might have something to do with the silly 4WD vacuum motor and fork on the passenger side of the front differential. It kind of sounds like a rubbing sound like a bearing, like metal scraping an unevenly worn or rusted surface...not like a hard knocking sound like an engine knock or a pop from suspension or steering components. Anyone have any ideas or experience?
Possibly the wheel bearing? Depending on how bad it is I could image it might shut up under power. For a little anyway before it fails all the way.

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Old 02-12-2014, 10:25 AM   #3
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Like overkill said, it's possibly a wheel bearing. The YJ bearing unit wont show signs of wear until it is ready to disintegrate. Mainly because it's a bearing unit, instead of individual bearings like a vehicle with front hubs.

It could also be the CAD diaphragm not pulling the fork the whole way out of 4wd. Mine was like that, It would pull it back to disengage the axle but not far enough to clear the inner shaft completely. Causing the shift collar to rub the end of the inner shaft, since the outer shaft turns all the time with the wheel driving it.

I first fixed this by putting a posi-lok kit on it, then after a few cables, I went with the solid axle shaft and balanced front driveshaft for a permanent fix.
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Old 02-12-2014, 03:55 PM   #4
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Thanks guys I'll take a look but both front wheel bearings are less than a year old. I replaced them last spring.
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Old 02-12-2014, 10:50 PM   #5
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I second the CAD diaphragm because it happened on mine as well and I did the one piece shaft delete. After time I could not even engage my front axle because the CAD sleeve had worn down so bad.
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Old 02-13-2014, 05:32 AM   #6
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Check the CAD and the splined coupler inside. Sounds like its hanging and catching maybe. And dont rule out problems with the bearings whether you replaced em a year ago. Check em and retorque.
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Old 02-14-2014, 08:40 PM   #7
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Funny right after commenting on this the same exact thing happened to me. Was axle UJoint. Under power no noise at all, in 2wd would make all kinds of noise though.

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2wd only , 94 yj , front differential , knocking sound , wrangler

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