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Discussion Starter · #1 ·
I am new the forum here. This spring I purchased a 99 Sahara 4.0 5 speed and am loving it! Been wanting one for as long as I can remember and finally did it.

In the past couple of weeks my jeep has developed an extreme case of vibrations on takeoff and in 2nd gear, once in 3rd and beyond the vibration is very minor. The vibration is in the drive train as in the transmission is shaking, my shifter shakes. Up until today I thought I had an issue with the clutch/pressure plate. I have already checked out the motor and transmission mounts and they are in good shape.

Today on a whim at a stop light I shifted into 4WD high and wow the smoothest takeoff I have had in weeks. Absolutely no vibration whatsoever all the way through 5th gear. When I got back to 2WD, the vibration is back.

So now I am thinking it is not a clutch issue but something else. I have spent a couple of hours searching the web and found a few folks posting with the same symptom but no replies.

I am really hoping you folks and give me some pointers on this issue.

Thanks!
Brad
 

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Did you check the u-joints? Is the drive shaft/shafts properly balanced? How did you check the engine and transmission mounts?
 

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Discussion Starter · #3 ·
Visual inspection on the mounts, no cracks bolts tight. For the motor mounts I had someone rev the engine while I watched under the hood and no movement.

I was thinking that if it was a clutch/motor mount issue it would happen regardless of 2WD or 4WD, that is why my suspicion changed today.

I have not had a chance to look at the u-joints yet.
 

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I'd check the motor mounts while you're putting the engine under a load. Revving an engine is not a good way to check motor mounts, unless they're totally shot. If they're on their way out you might not detect the problem. Been there done that. Block and chock the wheels, apply the emergency brake put the Jeep in first. Have someone off to the side, in a safe spot watch the engine for abnormal movement as you release the clutch. You want to immobilize the vehicle. It's easier with an automatic transmission.

Slight movement is normal. You do have to know what you're looking for with regard to normal. I've seen engines raise up to one side with bad mount/mounts.
 

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Shifting into 4Hi reduced the amount of torque being sent to the rear axle. No changes to the rear axle as in any pinion angle change? If not, I'd probably first look at the rear driveshaft u-joints.

Any u-joint bearing cap movement as you twist the rear driveshaft back & forth hard? Any signs of dry looking rust coming out of any of the u-joint bearing caps?
 

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You didn't mention the mileage on your new Jeep, also do you hear any creaking or squeaking on take off? either is a sure sign of rear driveshaft U-Joints needing replacement.
 

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Discussion Starter · #7 ·
Thanks for the replies. 193k miles. I will inspect the rear driveshaft and let follow up with what I find hopefully that is all. No sounds on takeoff, just vibrations.
 

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You cannot really inspect driveshaft u joints without removing the shaft and then feeling the u joint thru its range of flex on each axis as a bond can cause very significant vibration bounce that is usually speed dependent

Makes little sense that goes away in 4WD

Try it another time

Might also try a short drive with rear drive shaft removed

Sounds more like clutch chatter than anything else but should still be there in 4 wd


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Zi have had the same issues on a 2006 and 2010.
On both, I replace the sway bar and added better shocks. There is a term 'death wobble' that describes the issue. Scared the crap out of me the first time.
After replacing no issues!
I used Rock Auto, by the way.
Good luck!
 

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Zi have had the same issues on a 2006 and 2010.
On both, I replace the sway bar and added better shocks. There is a term 'death wobble' that describes the issue. Scared the crap out of me the first time.
After replacing no issues!
I used Rock Auto, by the way.
Good luck!
From what he described it has more to do with driveline issues than steering.
 

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Take off issues would be driveline, usually rear u joints, 'Death Wobble' is an issue after the Jeep is moving and usually at speed.
 

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Discussion Starter · #12 ·
To follow up on this. I inspected the rear ujoints yesterday, put in neutral and climbed under and it was very obvious the ujoint on the transmission side was shot. There was a good big of play when pushing the shaft back and forth and visually I could see the rubber seal on 2 of the caps was gone. I have a picture of the joint and caps after taking them out, i'll try to figure out how to post here. Replaced both the the ujoints with moog and it drives like a Cadillac now!

Thanks for your pointers. I was for sure it was a clutch issue.
 

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That ujoint has definitely been shot for a long time.
 
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