Harmonic Oscillation at Freeway Speed - JeepForum.com

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post #1 of 17 Old 10-02-2013, 02:29 PM Thread Starter
cjhsa
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2002 KJ Liberty 
 
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Location: Grand Rapids
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Harmonic Oscillation at Freeway Speed

My KJ has done this for a long time, but it seems to be getting worse. Above 70MPH, you'll hear it start, a low rumble at first, and eventually the entire tailgate is vibrating. My latest indy mechanic says he thinks it's in the rear diff (of course, there's money in doing diff work). I have seen that some KJ's came with harmonic dampeners attached to various parts of the drivetrain. Where exactly might these be? Did all KJ's have them?

Or any other ideas what this might be? I've already had a road force balance done on the wheels/tires. Alignment seems to be fine, brakes are new. Help!

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post #2 of 17 Old 10-02-2013, 02:32 PM
USPLiberty
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It's probably the tires. Uneven wear/out of round. You can check for yourself, remove one of the rear tires and roll it down the sidewalk. My old tires were really wobbly, uneven and past due for a change.
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post #3 of 17 Old 10-02-2013, 02:55 PM
tommudd
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Check rear boot on the front driveshaft to see if it needs replaced
check rear ujoints as well, they will seem tight but lots of them are just rusted solid almost

04 KJ WITH JBA 4 INCH COILOVER LIFT
03 KJ WITH 2.5 TOTAL CONTROL LIFT
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post #4 of 17 Old 10-02-2013, 03:14 PM
coolin4u
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Do you by chance have vent shades on the side windows? I no longer have mine but shortly after purchasing it i developed a very similiar problem,after repeated trips back to the dealership it was found to be those stupid vent shades.I know it sounds crazy but removing them cured the problem
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post #5 of 17 Old 10-03-2013, 06:43 AM Thread Starter
cjhsa
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No vent blades and the u-joints were inspected and passed with flying colors. Or so they said. The tires are a year old tops. Cooper Discoverers. The front driveshaft was replaced about two years ago.
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post #6 of 17 Old 10-06-2013, 09:25 PM
atkinson
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I have the same thing going it starts at 49 mph to 56 mph. I remove the front drive shaft and rotated the rear drive shaft at the york no change. I install new cooper tires no change, maybe rear axle bearing ,carrier bearing or maybe pinon bearing . Any ideas will be helpful. Or I GUESS I WILL HAVE TO GET MY HANDS DIRT.
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post #7 of 17 Old 10-06-2013, 11:19 PM
USPLiberty
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Are you sure that your front wheels are aligned? How do the treads look? Any outside feathering?



I had a noticeable positive camber and my tires made a persistant "wub wub wub" sound at that speed. It sort of got less noticeable after 60 mph but I could still hear it. When I got my latest tires, these guys knew what they were doing and set the camber correctly = quiet as possible for all speeds.
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post #8 of 17 Old 10-08-2013, 12:08 PM Thread Starter
cjhsa
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I don't see any obvious feathering. Three of the four tires appear to be slightly more worn around the outer edge, but not much.
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post #9 of 17 Old 10-08-2013, 02:05 PM
atkinson
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Install new ball joints and a alignment and its still there.
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post #10 of 17 Old 10-09-2013, 07:57 AM Thread Starter
cjhsa
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Where are those dampeners located? They look like big versions of the stabilizers you put on a compound bow.

Also, this is lipstick on a pig, but Jeep clearly did a fair amount of work on the tailgate to keep it from vibrating at speed. The guide about a foot below the latch is one clue, as are the rubber bushings in the mating piece on the gate. Can the tailgate be tightened up to mitigate the excessive noise from the vibration?
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post #11 of 17 Old 10-09-2013, 08:08 AM Thread Starter
cjhsa
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I found this, but I'm not clear on the terminology:

http://www.justanswer.com/jeep/65h63...djustment.html
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post #12 of 17 Old 10-10-2013, 11:44 AM
kiwibert
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I have had the same issue - between 70 and 80mph -for a long time.... now with 175k on the odometer and have decided to check out and perhaps replace the driveshaft u-joints. There is a bit of play in the rear wheel bearings so that is the next possibility, but more expensive. Didn't go away with new tires, all balanced. So now the search is on as it is getting worse.
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post #13 of 17 Old 10-11-2013, 04:47 PM Thread Starter
cjhsa
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Hey kiwibert, let me know if the u-joint replacement helps. I was told mine are fine, but was leaning towards replacing them anyway. That and checking for "surprises" in the rear diff by getting the fluid changed.
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post #14 of 17 Old 10-22-2013, 09:59 AM Thread Starter
cjhsa
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Well, it's getting worse. I'm leaning towards taking it to the stealership and see what they have to say. They might be able to put a different set of wheels/tires on it and see if it makes a difference. If not, with the $1500-$2000 "quote" I got before to rebuild the diff, just put in a new diff instead?

What diff(s) did the 2002 Liberty Sport 4x4 3.7L use? I looked at rockauto.com and they had several, ranging from a very reasonable $322 to about $900.

DANA HOLDING CORP Part # DS73100 TracLoc Positraction, complete; 29 Spline; 2.56 and up
For Diff : Chrysler 8.25", Rear Differential, with 29 Splines, 4WD
For Diff : Chrysler 8.25", Rear Differential, with 29 Splines, RWD (Only 4 Remaining)
$321.79

EATON Part # TT912A569 True Trac Limited Slip; 3.54 & up
Rear; RWD; AMC Model 35, WJ Grand Cherokee; 27 Spline
Rear; 4WD; AMC Model 35, WJ Grand Cherokee; 27 Spline (Only 3 Remaining)
$471.79

EATON Part # TT912A553 True Trac Limited Slip
Rear; 4WD; Chrysler 8.25", '97-'04; 29 Spline
Rear; RWD; Chrysler 8.25", '97-'04; 29 Spline (Only 1 Remaining)
$648.99

EATON Part # EAT19817 E-Locker; 3.54 & down
Front; 4WD; Dana "Super" 30, Jeep Liberty; 27 Spline (Only 1 Remaining)
$896.79

EATON Part # EAT19818 E-Locker; 3.73 & up
Front; 4WD; Dana "Super" 30, Jeep Liberty; 27 Spline (Only 2 Remaining)
$896.79
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post #15 of 17 Old 10-22-2013, 12:03 PM
USPLiberty
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Before you buy a new front differential, have you tried to pull the CV axles out and go for a test drive? It would be a cheap test for you to try, just a little time consuming. Don't forget to temporarily stuff a clean rag into the open differential holes if you pull out passenger side shaft too.
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