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Unread 10-17-2011, 10:24 PM   #1
nickrad8
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Join Date: Sep 2011
Location: manchester, nh
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Rear End Vibration

I have a 99 sahara that i just replaced the frame on. the reason for the frame replacement was because of the amount of rot on the original frame. the rear upper control arms (both) rotted completely off and may have messed up my rear diff. i have a dana 35 in the rear. when i accelerate, i feel an unusual vibration from the rear end. the jeep is lifted 2.5 inches and the transmission skid is lowered about an inch. i cannot figure out the source of the vibrations. they only occur at around 1800 RPMs and 2800 RPMs. i figured the frame swap would fix the problem but it still occurs. prior to the frame replacement, i pulled the rear diff cover and noticed a lot of metallic sheen in the fluid and some sand grain sized metal shavings in the bottom. i cleaned the diff and filled with new fluid to try to see if that would help. it didnt. while i had the diff cover off, i also noticed that one of the teeth on the Ring was slightly chipped but only saw one tooth that seemed to be damage.

any ideas on how to fix this? or what may be the cause of the vibrations?

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Unread 10-17-2011, 11:06 PM   #2
RaggedOleMan
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2005 TJ Wrangler 
 
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Location: , Sane's Ville
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Quote:
Originally Posted by nickrad8 View Post
I have a 99 sahara that i just replaced the frame on. the reason for the frame replacement was because of the amount of rot on the original frame. the rear upper control arms (both) rotted completely off and may have messed up my rear diff. i have a dana 35 in the rear. when i accelerate, i feel an unusual vibration from the rear end. the jeep is lifted 2.5 inches and the transmission skid is lowered about an inch. i cannot figure out the source of the vibrations. they only occur at around 1800 RPMs and 2800 RPMs. i figured the frame swap would fix the problem but it still occurs. prior to the frame replacement, i pulled the rear diff cover and noticed a lot of metallic sheen in the fluid and some sand grain sized metal shavings in the bottom. i cleaned the diff and filled with new fluid to try to see if that would help. it didnt. while i had the diff cover off, i also noticed that one of the teeth on the Ring was slightly chipped but only saw one tooth that seemed to be damage.

any ideas on how to fix this? or what may be the cause of the vibrations?
Get down on your knees & view the angle/relationship of the drive shaft to the pinion from the side of your rig. They need to be "inline" with each other. In other words, there should be little to no angular change between the pinion & the drive shaft at the u-joint while at ride height.
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Unread 10-18-2011, 10:43 AM   #3
nickrad8
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so in other words where the rear diff meets the u-joint should be level with the ground and same thing where the transmission meets the u-joint? im not sure if i said that right.
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Unread 10-18-2011, 11:54 AM   #4
nickrad8
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do you know what angle the drive shaft should be at? and could it be the bearings in the differential? or would that cause a constant vibration at every speed/RPM?
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Unread 10-18-2011, 12:46 PM   #5
RaggedOleMan
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Quote:
Originally Posted by nickrad8 View Post
so in other words where the rear diff meets the u-joint should be level with the ground and same thing where the transmission meets the u-joint? im not sure if i said that right.
No...not level with the ground...

The u-joints on the end(s) of your DS allow for angularity between the DS & pinion as the axle & suspension cycles. However, while at ride height there should be little to no angulation between the pinion & the DS, while there may be some at the TC end. Also, do you have a slip yoke or SYE & CV DS, I forgot to double check your profile...?

If you don't have a clue what I'm talking about, I strongly encourage you to visit with a competent mechanic familiar with 4wd vehicles in your area. Or someone that's better at expressing themselves in print than I am. Good luck.

EDIT; You have to fill in your profile to get competent help...
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Unread 10-18-2011, 01:38 PM   #6
nickrad8
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I don't believe I have an SYE I will check when I get home tonight. I will also upload a picture for you. I just looked at the FSM to see if I could find a picture of what you were talking about and I think I understand what you are saying. When the jeep is parked, the driveshaft should look like it is a solid extension from the rear end as if there was no u joint between the rear diff and drive shaft. I don't think I have a CV drive shaft either. I apologize for not having my profile filled out. I forgot to do it
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Unread 10-18-2011, 05:52 PM   #7
nickrad8
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I figured out the issue. I forgot to install the transmission skid plate spacer. Thanks for the help
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Unread 10-18-2011, 07:11 PM   #8
NakedCreekTJ
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okay so im having a similar issue. while in 3rd gear and accelerating, my jeep vibrates like its a race car or something. haha, but in all seriousness is this something i should be concerned with? the jeep has a 2.5" lift and only has 30" tires. Also, im almost certain it has spacers on the skid plate...
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Unread 10-18-2011, 09:42 PM   #9
nickrad8
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does it happen while accelerating at any speed in third gear?
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Unread 10-19-2011, 10:29 AM   #10
NakedCreekTJ
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Yea from what I've noticed it does.
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