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post #1 of 21 Old 10-18-2018, 10:47 AM Thread Starter
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Vibration problem

Hi,
this is my first post. I have a 2008 auto JKU. I have not been able to get a diagnosis of the following problem: the car vibrates when between 1,000 and 1,300 rpm and moderate to heavy load. In any gear. For example, of I'm going 50kms per hour and my rpm's are at about 1,200 (maybe in 4th gear, I don't know) and I start going up a hill, or want to accelerate, it starts to vibrate and vibration gets worse and worse if I keep the gas pedal there. If I let go of the gas pedal, it stops (I don,t have to let go completely). If I press harder on the gas pedal and force it to upshift (force it into higher revs), it stops. This can happen in any gear where I am at low rpms and never above 1,500 rpm.

It is not my tires, they are balanced; plus when It upshifts, the vibration goes away although the wheels are still turning at the same speed. I feel it is some part that is turning and is out of balance, and if that part spins fast the vibration goes away, but can't figure out which part. I thought it might be the drive shaft but it still has the balancing weights on it intact, so it can't be that. I never offroad (well...once years ago) so nothing should be bent. Any suggestions?
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post #2 of 21 Old 10-19-2018, 05:36 AM
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Drive it harder, give it some time. It may fix itself. If it gets worse it will be easier to find.
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post #3 of 21 Old 10-19-2018, 05:54 AM
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pull driveshafts one at a time then test w/out one driving then w/out the other (yes. you can drive w just front DS far enough in 4wh to test this) cuz this sounds like a Rzeppa CV goin. also check your transfercase fluid level .



i know the sound youre talkin about ...i bet its the rzeppa joint ' it doesnt make it except under load. pull the DSs 1 atta time and see....





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post #4 of 21 Old 10-19-2018, 06:30 AM Thread Starter
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It does not necessarily vibrate under load (and there is no sound what so ever, just vibration coming from right under me). It vibrates under load + low rpm. If I am at 2,000 rpm, let's say, and I WOT, it will just take off like new. If it was the CV joint, it would vibrate under load no matter the rpms, no? Plus, it's like a harmonic resonance, If I don't let off the gas when it starts vibrating, the vibration will get harder and harder even though I'm not going any faster (think going up a hill, you give more gas to maintain speed - and it starts vibrating and vibrations get harder even though speed is constant). Vibrations stop the second I lift my foot off the pedal, or I press harder to force an upshift.

I really feel it is some type of rotating piece that is out of balance because the vibrations feel very much like an out of balance wheel. Can it be the flywheel inside the transmission? Could it be bent because of heat somehow, and is vibrating at certain rpms? My transmission oil was completely black (changed it two months ago - not a flush - thanks to the advice I read here!).

The car has 200,000kms btw.
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post #5 of 21 Old 10-19-2018, 06:31 AM Thread Starter
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Quote:
Originally Posted by GobiRecon View Post
Drive it harder, give it some time. It may fix itself. If it gets worse it will be easier to find.
...and possibly more expensive to repair
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post #6 of 21 Old 10-19-2018, 06:51 AM
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Originally Posted by 2008wranglerjku View Post
...and possibly more expensive to repair
Any suggestions?
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post #7 of 21 Old 10-19-2018, 07:01 AM
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Originally Posted by j3ff3ry_j33p View Post
pull driveshafts one at a time then test w/out one driving then w/out the other (yes. you can drive w just front DS far enough in 4wh to test this) cuz this sounds like a Rzeppa CV goin. also check your transfercase fluid level .



i know the sound youre talkin about ...i bet its the rzeppa joint ' it doesnt make it except under load. pull the DSs 1 atta time and see....



I agree with you on this one , every time there is a vibe issue on a JK with very many miles it has always been the front joint at the transfer case in my personal experience .One self destructed it self and dented the crap outa the trans pan too .
Do what Jeffery said and just remove the front shaft and then drive it , I'd be willing to bet that it will be that joint that is worn and causing the vibe .
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post #8 of 21 Old 10-19-2018, 07:39 AM Thread Starter
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Thanks for the reply but I am confused. You think I should remove the front drive shaft and drive, meaning the DS powering the front wheels? Or do you mean the problem is the front CV joint of the rear DS? I understand the rear DS has a CV joint on both ends, are you saying the problem might be the CV joint at the front side of the rear DS, or the front DS? Sorry I am not very familiar with the jeep's drive train. Btw, both CV joints on the rear DS are visually perfect and make no noise.

Is the suggestion to take out the rear DS, put it in AWD mode to engage the front DS, and drive to see if the vibration goes away?
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post #9 of 21 Old 10-19-2018, 10:59 AM
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Originally Posted by 2008wranglerjku View Post
Thanks for the reply but I am confused. You think I should remove the front drive shaft and drive, meaning the DS powering the front wheels? Or do you mean the problem is the front CV joint of the rear DS? I understand the rear DS has a CV joint on both ends, are you saying the problem might be the CV joint at the front side of the rear DS, or the front DS? Sorry I am not very familiar with the jeep's drive train. Btw, both CV joints on the rear DS are visually perfect and make no noise.

Is the suggestion to take out the rear DS, put it in AWD mode to engage the front DS, and drive to see if the vibration goes away?
Remove the FRONT DRIVE SHAFT and then drive it and see if you can replicate the vibe , If it persists replace the front and then Remove the REAR DRIVE SHAFT and drive it to see if you can replicate the vibe .

If neither of these tests results in a symptom identification , you will need to look else where .
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post #10 of 21 Old 10-19-2018, 11:06 AM Thread Starter
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Thank you for your reply, but perhaps I should have mentioned the vibrations occur when I'm on rear wheel drive (not awd), so it has to be the rear drive shaft, I guess there's no point in pulling the Front DS, correct? Also, I noticed there are balancing weights on both ends of the rear DS. I checked only one end (to see if a weight has fallen off), but I didn't check the other end as I did not know previously there are weights on both ends. I will check for those too. My jeep is at my county place so I only have access to it on the week-ends (going there tonight), so I will report back. The rear DS is also very rusted (will post pictures Monday), I wonder if that could have thrown it out of balance. It's REALLY rusted, 10 years of salt (I live in Montreal, Canada), you'll see with the pictures.

I appreciate all the help! Have a great week-end everyone!
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post #11 of 21 Old 10-19-2018, 11:54 AM
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Quote:
Originally Posted by 2008wranglerjku View Post
Thank you for your reply, but perhaps I should have mentioned the vibrations occur when I'm on rear wheel drive (not awd), so it has to be the rear drive shaft, I guess there's no point in pulling the Front DS, correct? Also, I noticed there are balancing weights on both ends of the rear DS. I checked only one end (to see if a weight has fallen off), but I didn't check the other end as I did not know previously there are weights on both ends. I will check for those too. My jeep is at my county place so I only have access to it on the week-ends (going there tonight), so I will report back. The rear DS is also very rusted (will post pictures Monday), I wonder if that could have thrown it out of balance. It's REALLY rusted, 10 years of salt (I live in Montreal, Canada), you'll see with the pictures.

I appreciate all the help! Have a great week-end everyone!
Given that there are no locking hubs on stock JKs your front shaft spins regardless of your t-case drive selection, may not be putting power to the front but it still spins thus the request from multiple folks to follow the outlined procedure to isolate individual d-shafts.
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post #12 of 21 Old 10-22-2018, 06:03 AM Thread Starter
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Given that there are no locking hubs on stock JKs your front shaft spins regardless of your t-case drive selection, may not be putting power to the front but it still spins thus the request from multiple folks to follow the outlined procedure to isolate individual d-shafts.
Ok now that's very pertinent information, I had completely ignored the front DS thinking it would not turn unless in AWD. Thank you so much for that. I was not able to get under the jeep this week-end so I have no updates, but will post as soon as I have (probably in 2 weeks). Again, thanks everyone for your help.
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post #13 of 21 Old 10-22-2018, 06:16 AM Thread Starter
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Also, there's something that's bothering me though...doesn't the DS's turn the approximate speed of the tires? I understand there's a gear ratio, but I mean don't they turn faster as the wheels spin faster, unlike the engine rpms which vary up and down depending on gear selection? i'm asking because for a given wheel speed, I will experience vibrations below 1,500 engine rpm but wont, if, at the same wheel speed (and hence same DS rpm), I go into a higher gear (or should I say taller, from 3rd to 2nd) and bring the engine rpms higher (to 2,000 for example).

- scenario 1: 50kms/h at 3rd speed at 1,200 engine rpm = vibration
- scenario 2: 50kms/h at 2nd speed at 2,000 engine rpm - no vibration.

In both these scenarios, the vehicle speed is the same, therefore isn't the DS speed also the same? And if this is true, shouldn't I experience a vibration in both cases if the vibrations were DS related (bent or imbalanced)?

I know the best way to find out is to follow the suggestion in the above posts, and I will do that, but I'd just like to understand the theory behind it. Thanks!
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post #14 of 21 Old 10-22-2018, 08:19 AM
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Yes you are correct, anything that varies with wheel speed is somewhere beyond the output of the transmission (drive shafts, transfer case, anything in the axles, etc.). Anything that varies with engine RPM is somewhere before the input to the transmission (engine, things on the serpentine belt, etc.).

Or in either case it could be something inside the transmission since both input and output speeds are in the transmission so the information doesn't help if it's the transmission, although it would tell you what to look at while rebuilding the transmission.
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post #15 of 21 Old 10-22-2018, 08:34 AM
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Im going to throw out a swag and say it's that the control arm bushings are shot and allowing the diff to rotate and that's putting an odd angle on the driveshaft creating a slight bind. Same thing happens when we lift them which is why we put adjustable control arms on. I'm going to bet on it being the rear diff since it does it all the time. Shifting to a lower gear takes the load off and it goes away. Of course it could also be a pinon bearing but I doubt it, that makes noise most all the time.
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post #16 of 21 Old 10-22-2018, 09:51 AM Thread Starter
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Originally Posted by sschefer View Post
Im going to throw out a swag and say it's that the control arm bushings are shot and allowing the diff to rotate and that's putting an odd angle on the driveshaft creating a slight bind. Same thing happens when we lift them which is why we put adjustable control arms on. I'm going to bet on it being the rear diff since it does it all the time. Shifting to a lower gear takes the load off and it goes away. Of course it could also be a pinon bearing but I doubt it, that makes noise most all the time.
This would make sense as the second I ease off the gas (staying in same gear), it stops immediately. Are the control arm bushings something I could inspect visually, are there any 'tricks' to test them?
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post #17 of 21 Old 10-23-2018, 04:59 AM
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don't go chasin rabbits; KISS and pull the front DS then the rear. Inspect both at their respective times while out ( just good maint) , drive to check vib status and go from there.

CA bushings might be worn but you're gonna hear more clunks when that is evident, not harmonic vibs as much.


Start with the most common , diagnostic strtng-pnt and report back once you've verified the shafts. (no offense to anyone as all these sggtns are appropriate)






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post #18 of 21 Old 10-24-2018, 06:03 AM
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Originally Posted by 2008wranglerjku View Post
This would make sense as the second I ease off the gas (staying in same gear), it stops immediately. Are the control arm bushings something I could inspect visually, are there any 'tricks' to test them?
Pretty easy to check, just disconnect them at the axle and then visually check them for wear. Dont disconnect the frame side, if it is sloppy then the bushings are shot. If they are shot you might consider replacing them with adjustable's. Even if it doesnt solve the problem it's a great upgrade.

I'm assuming you know to remove the rear wheels and use jack stands, wheel chocks, etc.
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post #19 of 21 Old 10-24-2018, 09:07 AM
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Originally Posted by sschefer View Post
Shifting to a lower gear takes the load off and it goes away. Of course it could also be a pinon bearing but I doubt it, that makes noise most all the time.
Thing is happens at low RPM, but goes away at higher RPM (more power). Seems pretty amazing to me if that could be anything transfer case or beyond.
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post #20 of 21 Old 05-18-2019, 02:03 PM Thread Starter
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OK, so I left it in the garage all winter, and today I was changing oil and noticed some rubber missing on the harmonic balancer. I don't know how to post pictures, but it's pretty obvious to me my jeep has a harmonic UNbalancer. I will get that replaced and report back if the issue is resolved.
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post #21 of 21 Old 05-18-2019, 10:01 PM
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Iíll bet itís no problem for your ol lady
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