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Discussion Starter #1
Just bought a 2003 as a salvage project: needed a front suspension including axle, lower control arms, and shocks due to a front end collision (exact circumstances unknown). All done, and successfully inspected, however whenever applying throttle there is a very distinct drone/rumble/vibration/growl that permeates through the entire vehicle.

symptoms:
* occurs ONLY under accel; as soon as you lift the throttle it goes away
* begins almost immediately as the vehicle starts to roll
* the severity of the vibration is proportional to the throttle (worse with more throttle)

vehicle condition:
* overall excellent condition
* new ball joints, shocks, LCAs
* brand new tires (33" BFG mud terrains)
* frame professionally trued and measured
* aligned, with caster set at mid-spec
* 4" lift
* u-joints SEEM ok, but not thoroughly inspected
* rear axle untouched

It seems to me that it's goign to be driveline related, but short of putting a stethoscope on the rear axle while on stands, or pulling the cover, not sure what the usual suspects might be. Hopefully someone on this board can point me in the right direction. Thanks!
 

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Very well could be a Driveline U-joints. I had that same accelleration vibration on a different vehicle (1 ton truck) and it was the U-joints...they had no extra play in them, just shot.
 

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Drivetrain vibrations that only occur during acceleration are usually caused by the rear driveshaft u-joints vibrating from either an excessively high pinion angle (when modifications have been made to allow that) or a bad u-joint in the driveshaft. Both of those would be my immediate first suspects. But that you have a 4" suspension lift makes me think that your u-joint angles are simply excessive. Fixing those excessive angles is best done with a SYE kit and aftermarket CV driveshaft. Dropping the t-case via spacers can also reduce the excess angles but I doubt you could drop it enough within reason to cure the vibrations from such a tall suspension lift. With a 4" lift, installing a SYE (slip yoke eliminator) kit into the transfer case and aftermarket CV driveshaft is the right solution. Good luck with it. :)
 

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Sounds like you need to lower your transfer case skid or add a slip yoke eliminator and a new rear drive shaft. The 2nd suggestion is the better but more costly way of correcting the problem. When you add lift it increases you factory rear drive shaft angle past a point that it can properly function at.
 

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Is it a 4sp auto?
 

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Discussion Starter #6
fwiw, its a 5-spd 4.0L.
i wouldn't have thought the 4" lift would have compromised the joint angle THAT much, lots of jeeps with that amount of lift. i mean the level of vibration is unsettling... i drove to the inspection station this morning no faster than 45 mph (80 mile RT) cause i thought i was either slowly destroying something or it would suddenly gernade/seize.
i'll check the joints tonight.
 

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fwiw, its a 5-spd 4.0L.
i wouldn't have thought the 4" lift would have compromised the joint angle THAT much, lots of jeeps with that amount of lift. i mean the level of vibration is unsettling...
With a short wheelbase Wrangler, as the TJ is, you will get u-joint vibrations with any lift height taller than 2"... and often only with 2". 4" is a lot of lift and any TJ with 4" of lift and no vibrations will have had work done to eliminate those vibes... usually by installing a SYE kit and CV driveshaft. No way can a stock TJ have a 4" suspension lift without vibrations. Those "lots of Jeeps with that much lift" all had something done to them to reduce the u-joint angles back to how they were when the factory shipped the Jeep.
 

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With a short wheelbase Wrangler, as the TJ is, you will get u-joint vibrations with any lift height taller than 2"... and often only with 2". 4" is a lot of lift and any TJ with 4" of lift and no vibrations will have had work done to eliminate those vibes... usually by installing a SYE kit and CV driveshaft. No way can a stock TJ have a 4" suspension lift without vibrations. Those "lots of Jeeps with that much lift" all had something done to them to reduce the u-joint angles back to how they were when the factory shipped the Jeep.
Yup, threw a 2.5" lift on mine and had to drop the TCase to get rid of the vibes. Saving up for my SYE as we speak. With a 4" lift, a tcase drop may not even be an option for you, but I'd let the pros weight in on that one.
 

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Discussion Starter #9
...not be argumentative, but it makes the damn rear-view mirror blurry and my ass numb!!! that's a shit load of vibration!
anyways, ujoints were fine but i think i found the culprit: a broken/sheared transmission cross-member mount. I cant exactly rationalize how that would translate to this type of vibration, but as soon as i can replace and road test i'll post back. thanks for the help guys.
 

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...not be argumentative, but it makes the damn rear-view mirror blurry and my ass numb!!! that's a shit load of vibration!
anyways, ujoints were fine but i think i found the culprit: a broken/sheared transmission cross-member mount. I cant exactly rationalize how that would translate to this type of vibration, but as soon as i can replace and road test i'll post back. thanks for the help guys.

The first thing you need to do before replacing anything is to determine if the slip yoke on the rear shaft has been eliminated and replaced by an SYE and CV shaft or whether there is a transfer case drop.

Like Jerry said it is unlikely that you will be able to reduce the driveline angle enough with only a transfer case drop so a SYE and CV shaft is the only realistic solution for vibration when you have a 4" lift.

If you don't have this, this IS the cause of your vibration. We are not guessing. It takes but merly a minute to check if you have the correct rear shaft setup. Why not check?
 

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Discussion Starter #12
The first thing you need to do before replacing anything is to determine if the slip yoke on the rear shaft has been eliminated and replaced by an SYE and CV shaft or whether there is a transfer case drop.
ok, so i'm not much of a jeep expert (note my avatar is NOT a jeep), so not sure what a SYE looks like. But i can tell you three things for SURE: the rear drive shaft has u-joints not CVs, there is no t-case drop, and that the trans mount had completely sheared. the local parts store has the mount in stock... story at 11.
 

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Can you post a pic of the rear driveshaft, and rear axle showing pinion angle?

Another question: was there any damage to the transfer case as a result of the front end damage? Many times in a frontal collision, the front drive shaft will be forced back into the tcase and cause internal damage, which potentially could result in the symptoms you described.
 

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Discussion Starter #14
success, mostly. replacing the broken trans mount definitely improved the severity of the vibration, but (as i was warned by everyone!) there is still a fairly pronounced vibration under power. while i was under the jeep i took some measurements, and then started playing with a spreadsheet to see the effect of various angles.

so here's a few conclusions:

* any driveshaft angle at all creates cyclic speed fluctuations in the DRIVESHAFT. the greater the angle, the greater the fluctuations. some folks claim this is the source of the vibration (it is in fact, vibrating, albeit torsionally). theoretically if you take anything with mass and accelerate it and decelerate it rapidly (ie, vibration) then those forces will be felt. basically, its a F=ma type thing. However, my contention is it's NOT the primary source of vibration, since removal of torque transfer (lifting throttle) reduces virtually all the vibration i'm feeling, and that shouldnt have anything to do with this type of vibration since neither 'm' nor 'a' have changed.

* any misalignment between the transmission/t-case and axle will result in speed fluctuations at the AXLE. in my case, it's significant due to the 4" lift which rotated the axle pinion upwards. if the tcase and axle are aligned/parallel then the speed variations are cancelled out and the axle rotates at the exact same speed as the tcase. due to my misalignment there is a ±2% speed variation which is felt as a pulsing sensation. i think that when you chop the throttle, there is enough slop/lash in the drivetrain that those vibrations disappear.

so, rather than CVs, i wonder if longer LCAs in the back would realign things enough and remove the drone...

(btw, i'll share the spreadsheet but cant figure out how to upload)
 

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If getting rid of that type of vibration was as easy as simply changing the rear pinion angle by adjusting control arm lengths, we wouldn't be paying $$$ to buy and install SYEs and CV driveshafts once we get to 4" and taller suspension lifts.
 

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I seem to have a similar vibration? I noticed it last week and it became really bad when I had three people in the Jeep. It seems that with one extra adult in the back seat the vibration increased substantially for some reason? Anyhow I have a 2" Suspension lift and a transfer case drop. The Jeep has been fine for the last 12 months but suddenly this vibration has come about. Still searching for the source? Drive shaft universal joints appear tight. If the driveshaft angle was bad I would expect the problem from the day the lift went in?
I am sorry I can't offer any help here but others may have similar experience and located the cause? Thank goodness for more knowledgable helpful people on this forum that might be able to enlighten us all.
:wavey:
 

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I have found it! The rear universal joint on my rear driveshaft had siezed. I was unable to find any play because there wasn't any play. Replaced u/j and problem fixed, yay! Might be your problem?
 

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Discussion Starter #18
so i decided to pop the rear diff cover off for a peek and this is what i found. ring gear looks perfect, and pinion too. but the spiders look AWFUL - heavy worn and pitted. i also noticed the fit between the spiders, cross pin, and housing is pretty sloppy - i'd estimate about 0.005" (they are visibly wobbly).

could this be responsible for the growl/drone, or is it pretty normal (yikes!)? how tricky a job to replace?
 

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Vibration/Drone sound

Okay so I have read everything above. I understand this post is a weee bit old, but thanks to google it steered me to this thread. I now have a 06 LJ Rubicon (Auto sadly) Now my quick story starts about 2 days ago... My truck was fine, took it threw some trails with a buddy (in 4H), everything seemed okay. Just yesterday the beach opened up, we were allowed to purchase a permit. I did, and decided to take my truck on the beach. NOTICED while in sand my truck was reving at 2k going about 7-10mph in (4H)... I didn't think something was right... but i haven't taken a vehicle on the beach in a while. While on the road (back in 2H) i have noticed a weird Vibration feeling at 30mph.. Then again at 50-60mph with a noisy drone/hum at this speed. I have thought it could be one of the following..

Tires missing a weight.
My shocks are bad.
Or a Transmission problem.

after reading this, i suppose a rear U-joint could be a suspect as well now... any ideas? Does my problem sound like it fits in this thread?:hide:
 
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