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Old 01-13-2009, 11:09 PM   #1
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Acceleration vibration

Hi my name is jason and im new to the whole jeep world, i picked myself up a used jeep wrangler the other day it is a 99' sport 4.0l with the automatic transmission and 80,000 miles on the odometer. I bought it off of guy that i work with for dirt cheap because it has a vibration problem and he isn't able to work on it do to certain disabilities and the lack of cash. Any ways the motor runs like a champ and the transmission shifts smoothly with no problems under mild acceleration. When your at a dead stop and you really get into the throttle it starts jumping and vibrating from the rear pretty bad. But if you dont get in the throttle to much on takeoff you would never know there was anything wrong with it. I have searched and came up with some similar problems that someone was having on a different forum but it was never resolved in their thread. Here is what i was thinking possibly the transmission mount is either worn or broke or maybe a motor mount. I haven't had time to look under it yet i haven't had the time to but was just wondering if anyone has had this problem or knows exactly what it is any help would be greatly appreciated thanks
jason
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Old 01-13-2009, 11:13 PM   #2
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Congrats on your Jeep, sorry I cant't tell what that is, post pics everybody loves jeep porn hahaha

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Old 01-13-2009, 11:15 PM   #3
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Is the problem only off the line or does it happen at any other speed? More information would be helpful. Welcome and nice Jeep.
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Old 01-13-2009, 11:16 PM   #4
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Is there a suspension lift installed? If there is, it could be nothing more than the rear axle's pinion angle having been set too high, as in someone tried to set the angle without knowing what they were doing. Vibrations that only happen during first-gear acceleration are very often nothing more than the rear pinion angle was set too high, causing a u-joint on the driveshaft to vibrate.

Can you take a photo of the driveshaft from the side showing the driveshaft and where it connects to the rear axle? I need to see the angle of the rear axle's pinion shaft where it connects to the driveshaft.

If there's no suspension lift, it could be a bent rear driveshaft or a bad u-joint on the driveshaft.

I'm guessing a rear pinion angle problem at this point however. Which while not serious or hard to fix, needs to be taken care of asap so the vibrations don't take out a bearing or seal.
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Old 01-13-2009, 11:17 PM   #5
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Its just off the line, you can cram the throttle in second and third on the highway and its fine
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Old 01-13-2009, 11:24 PM   #6
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i just replaced my tranny mount becuse of a banging i kept hearing. stock one was pretty much shredded. feels smoother but didn't fix the problem of the banging, turned out the rear track bar had snapped at the joint. fixing that next week. i had a bunch of vibration before the tranny mount was replaced. would be a good place to check. also check your control arms and make sure the bushings aren't shot.
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Old 01-13-2009, 11:57 PM   #7
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I tried to take some pics but its dark and its 9 degrees outside so im sorry that the pictures suck i will take some good pictures tomorrow before i leave for work and post them. Heres the pictures of the pinion angle and suspension im pretty sure the suspension is stock but may be wrong its currently sitting on 31" 10.50 all terrains that rub if you turn the steering to sharp
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Old 01-14-2009, 12:02 AM   #8
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Better pictures would help but it kinda looks like I was suspicious it might, the rear pinion angle could be too high.

With the stock rear driveshaft, the rear pinion angle must be parallel to the output shaft of the transfer case. Like in the below illustration. It shows 2 u-joints where yours only has one u-joint at the rear of the driveshaft but you can see how the pinion and transfer case angles must be parallel to each other.

The rear pinion angle should be equal to or it can be 1 or 2 degrees under the transfer case output shaft's angle but not even 1 degree above it.
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Old 01-14-2009, 12:11 AM   #9
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those appear to be factory links but the pinion angle does look high like you stated jerry........kinda freaky..im guessin wore out link bushings somwhere allowing that pig to roll up like that.....it actually looks really high unless its the angle of the pic
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Old 01-14-2009, 06:23 AM   #10
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My old 97 did just the same thing just before my rear U joint grenaded, every time. It also obviously had a nasty vibration under acceleration when the rear went too, but when the rear goes it always vibrates and gets worse with gas.
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Old 01-14-2009, 09:24 PM   #11
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Also forgot to mention, this same 1997 Jeep that had U-joint and rear end grenading issues also had a problem with incorrect gear ratios. After about 2 rear U-Joints and the rear end finally going out, the rear was replaced by a cheap shop in town. They put the wrong rear end in TWICE. Both times, there was obviously some vibration while driving, and it was much worse when accelerating. In 4wd, you could tell something was wrong. You might want to ask the previous owner if the rear end was replaced.

Also, I had the right rear shaft in the D44 in my Rubicon go bad. By bad, I mean bent in two places according to the warranty tech at the shop. I had some pretty odd and concerning vibrations when accelerating, and generally felt almost normal when not accelerating other than a pull to the right. But, if you had a bent axle shaft, you would also be having problems with axle seal leaks.
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Old 02-11-2009, 01:34 PM   #12
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well now that I got the jeep back from the body shop I can continue on with the vibration problem I got a chance to put it up on the lift and looked around to see if I could see anything obvious. I went over every bolt and nut on the back end of the jeep nothing is loose I did notice the transmission did have some play in it so I picked up a new mount and just finished installing it a few minutes ago. The install was fast and easy and didn't run into any problems except for the mess that I made in the garage man that thing was nasty under neath this summer I'm going to clean under neath and spray it with undercoat. Well went for a test drive and still having the same problem didn't fix it. I did notice that it dose it bad under a load like when the jeep is setting in a inclined position and you pin the throttle it really hops around bad in the rear. I don't know I'm clueless at this point thinking of taking it in to the jeep dealer and letting them diagnose it, its only $80 bucks and the guy said he would give me a list of part numbers of the things he finds wrong.
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Old 02-11-2009, 01:43 PM   #13
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Well, since you appear to be all stock back there and I'm not reading that anything is bent etc, what diff is back there? Is it open or does it have lim slip?

I wonder if you have a limited slip back there and it's sensing a loss of traction and/or in the process of going out on you.

Just thinking aloud...
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Old 02-11-2009, 01:52 PM   #14
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I bought it used I really don't think it has a limited slip but i could be wrong. It drives just fine going down the road no noises or vibes, its just upon fast takeoff and hard acceleration that it does it. You can just putt around in it and everything is fine. I'm kind of wondering about a possible motor mount being bad would that cause this.
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Old 02-11-2009, 02:09 PM   #15
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Well, since you said "starts vibrating from the rear pretty bad" I think most (at least me) are looking at drive line issues.

If it's more of an overall shaking you are getting, it could be a lot of things. Weak fuel pump, beginnings of bad plugs, dirty TPS, etc.

My TJ motor mounts have not needed replacing yet, so I'm not sure what the symptoms are for those, but it wouldn't seem to be related. Maybe give a different description of what's going on instead and have the crew here re-look at the facts again...
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Old 02-11-2009, 02:20 PM   #16
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Can you take a good sharp well lighted (use a flash) pic from the side that shows your rear driveshaft and especially the angle between it and the rear axle's pinion shaft and post it up here? Whoops, I just noticed you don't have 50 posts yet so you can't do that but if you will email it to me I'll post it for you.
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Old 02-11-2009, 02:58 PM   #17
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how much did you pick the jeep up for? if you dont mind..

I think the pinion is too high since its stock. how can that be? .. are the control arms bent in any way?
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Old 02-11-2009, 04:09 PM   #18
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As soon as the wife gets in from work I will take some good pics of the drive line so everyone can see pinion angles and suspension. There are no lift spacers or lift springs on this jeep everything is stock. The previous owner might of put rubi springs in it but I don't know its looks stock. I bought it with 31/12.50/15 tires and they don't rub except for full turn.
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Old 02-11-2009, 04:19 PM   #19
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how much did you pick the jeep up for? if you dont mind..

I think the pinion is too high since its stock. how can that be? .. are the control arms bent in any way?
Just half for what KBB has it listed for I just pretty much paid off what was left on the loan the guy owed he didn't want it.
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Old 02-11-2009, 06:07 PM   #20
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Originally Posted by Jerry Bransford View Post
Can you take a good sharp well lighted (use a flash) pic from the side that shows your rear driveshaft and especially the angle between it and the rear axle's pinion shaft and post it up here? Whoops, I just noticed you don't have 50 posts yet so you can't do that but if you will email it to me I'll post it for you.
These are the best I can get the weather not that great out.
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Old 02-11-2009, 06:24 PM   #21
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here are some more.
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Old 02-11-2009, 07:47 PM   #22
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Lot better pics but still don't see anything out of specs that I can tell.I had the same problem myself but mine ended up being the tranny mount had busted into 3 pieces.If you cann't figure it out I would start by pulling the diff cover.
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Old 02-11-2009, 10:43 PM   #23
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Originally Posted by stevens243 View Post
Well, since you said "starts vibrating from the rear pretty bad" I think most (at least me) are looking at drive line issues.

If it's more of an overall shaking you are getting, it could be a lot of things. Weak fuel pump, beginnings of bad plugs, dirty TPS, etc.

My TJ motor mounts have not needed replacing yet, so I'm not sure what the symptoms are for those, but it wouldn't seem to be related. Maybe give a different description of what's going on instead and have the crew here re-look at the facts again...
Hate to bump my own post, but...
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Old 02-13-2009, 05:47 PM   #24
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I checked the motor mounts today they seem to be good there is no movement at all with the motor had the wife get in and hold the brake and give it gas while I watched everything looked good. Is there suppose to be anything that supports the tranfercase or is the trans mount the only support on the tranny. Tomorrow I plan on taking out the drive shaft and checking out the universal joints.
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Old 02-13-2009, 05:59 PM   #25
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Your pinion angle looks fine. The entire drivetrain is held at three points, the two engine mounts and the rear tranny mount so that's all that is in the rear, the tranny mount. About the only way you can tell if that's bad is to drop the t-case skidplate and take a look at the mount. Remove the four nuts in the center of the skidplate which hold the bottom of the tranny mount in place first.
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Old 02-13-2009, 06:02 PM   #26
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I replaced the tranny mount a few days ago thinking that would cure the problem thats what I thought was really wrong with it all this time. Now im clueless checking the u-joints tomorrow I haven't ever seen a u-joint go out like this before but I could be wrong.
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Old 02-16-2009, 04:08 PM   #27
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I have did some intense searching over the past couple of days and I have found a thread over on the jeep forum with some people that have had the same issues as me this is exactly what is wrong with this jeep of mine but they did not come to a conclusion what it was here is the url to the thread if somone wants to take a look at it.

need help. new jeep, shudder on takeoff?? - JeepForum.com
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Old 02-16-2009, 06:18 PM   #28
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With what they are saying sounds the same as mine but I know what mine is.Baptized in the muddy water!!!! Water and ATF+4 do not mix well.I am just holding out as long as it will make it to rebuild my trans.Mine shutter and slips at first then after going it is fine.http://www.wranglerforum.com/f5/muddy-water-23562.html
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Old 02-16-2009, 07:59 PM   #29
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Back from the body shop? Was it in a wreck? If you tell us what happened it may give a big clue to the vibration.
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Old 02-17-2009, 07:10 AM   #30
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Back from the body shop? Was it in a wreck? If you tell us what happened it may give a big clue to the vibration.
I wish that was the case I would just make them fix it. This is something that the jeep had wrong with it when I bought it. I had it in the body shop because someone pulled out in front of me shortly after I bought it and caused a fender bender.

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