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Old 02-28-2019, 10:40 AM
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New gears, new problem! Bad vibrations!

Picked up my YJ yesterday from the shop just before they closed and drove it home. I like it that it feels spunky but holy hell it has a bad vibration at anything above 40 MPH. It really feels like driving on rumble strios or a giant cell phone vibrating under your seat. The gears installed were Elite Gears 4.88 with a complete install kit (bearings, etc), front and rear Truetracs and Ten Factory rear axle shafts.

I found a few threads where people had the same issues after new gears but really no solution.

I'm going to call the shop to see what they can do but I'm not holding my hopes too high.

I know the drivetrain is spinning faster now but didn't expect this. I will check the driveshaft today when I get home from work.

I good this issue can be resolved. No way I would feel comfortable driving at highway speeds with such vibration.

Anyone here experienced this and found a solution? Some of the old threads I read provide no solutions or the OP never provided updates.

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Old 02-28-2019, 11:12 AM   #2
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Originally Posted by MudderNuker View Post
Picked up my YJ yesterday from the shop just before they closed and drove it home. I like it that it feels spunky but holy hell it has a bad vibration at anything above 40 MPH. It really feels like driving on rumble strios or a giant cell phone vibrating under your seat. The gears installed were Elite Gears 4.88 with a complete install kit (bearings, etc), front and rear Truetracs and Ten Factory rear axle shafts.

I found a few threads where people had the same issues after new gears but really no solution.

I'm going to call the shop to see what they can do but I'm not holding my hopes too high.

I know the drivetrain is spinning faster now but didn't expect this. I will check the driveshaft today when I get home from work.

I good this issue can be resolved. No way I would feel comfortable driving at highway speeds with such vibration.

Anyone here experienced this and found a solution? Some of the old threads I read provide no solutions or the OP never provided updates.
Seems to be VERY commonly the driveshaft. Im not a YJ guy, but it has the vac disconnect on the front axle correct? So the front shaft shouldnt be spinning. Id have a look a the rear shaft, and see about getting it balanced.

All your wheel weights still on from balancing? some might have gotten knocked off during the install depending on where they were located and the type.

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Old 02-28-2019, 11:54 AM
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Maybe the moderator can move this thread to the tech forum. I created it on the wrong section.
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Old 02-28-2019, 11:55 AM
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Quote:
Originally Posted by MudderNuker View Post
Picked up my YJ yesterday from the shop just before they closed and drove it home. I like it that it feels spunky but holy hell it has a bad vibration at anything above 40 MPH. It really feels like driving on rumble strios or a giant cell phone vibrating under your seat. The gears installed were Elite Gears 4.88 with a complete install kit (bearings, etc), front and rear Truetracs and Ten Factory rear axle shafts.

I found a few threads where people had the same issues after new gears but really no solution.

I'm going to call the shop to see what they can do but I'm not holding my hopes too high.

I know the drivetrain is spinning faster now but didn't expect this. I will check the driveshaft today when I get home from work.

I good this issue can be resolved. No way I would feel comfortable driving at highway speeds with such vibration.

Anyone here experienced this and found a solution? Some of the old threads I read provide no solutions or the OP never provided updates.
Seems to be VERY commonly the driveshaft. Im not a YJ guy, but it has the vac disconnect on the front axle correct? So the front shaft shouldnt be spinning. Id have a look a the rear shaft, and see about getting it balanced.

All your wheel weights still on from balancing? some might have gotten knocked off during the install depending on where they were located and the type.
I will start troubleshooting this weekend. Going to call the shop first. Hopefully it is something simple like a driveshaft 180 rotation.
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Old 02-28-2019, 12:07 PM   #5
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Weird that the shop apparently didn't do a test drive after the install.
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Old 02-28-2019, 12:16 PM
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Weird that the shop apparently didn't do a test drive after the install.
They did but on secondary roads at around 40 MPH. The vibe starts at around 45ish. I just got off the phone with the shop they said to take it back. Crossing my fingers it is something they can solve.
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Old 02-28-2019, 12:25 PM   #7
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Maybe the driveline angles are off and because they are spinning faster this amplifies a vibration that may have gone unnoticed before the regear.
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Old 02-28-2019, 12:40 PM
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Maybe the driveline angles are off and because they are spinning faster this amplifies a vibration that may have gone unnoticed before the regear.
I'm planning on checking angles but I really have no clue as far as what are the tolerances. I recently installed one of the motor mounts that was shot and I loosened the TC bolts to allow for movement when the new one went in. The TC has the drop kit but I'm not sure it is the right amount of drop. My Jeep has a 3.5 inch (AFAIK) Dick Cepek lift. Maybe the rear axle pinion angle is off. The thing about it is that at the RPMs where the vibes occur were absent before the regear at the same or higher RPMs.
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Old 02-28-2019, 09:24 PM
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Took the Jeep back to the shop and they will look at it. One thing the became immediately obvious was that the pinion angle was pointing higher than the DS instead of being lower. They will adjust the pinion also. Crossing my fingers.
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Old 03-01-2019, 07:20 PM
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So I picked up the Jeep from the shop and it is much better now. It still has a distinct harmonic vibration about 60 MPH but not as strong as before. The mechanic removed the axle shims that were angling the pinion angle at above the driveshaft. Now the pinion angle looks much better according to what I found on the internet. Since I don't have a SYE and CV shaft the pinion angle should be parallel with the output shaft from the TC. I think I'm pretty close. In the picture the red line shows where the pinion angle was before removing the shims. The green lines shows the current angle.

I wonder if a SYE and CV will eliminate the rest of the vibes. Also, if I leave it like that what are the implications? The vibrations now are about half of what they were. I'm considering new u joints to eliminate that variable.

Thoughts?
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Old 03-02-2019, 02:40 PM   #11
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As with your other post, thanks. Can you describe what you're trying to demonstrate with the lines?
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Old 03-02-2019, 05:28 PM
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As with your other post, thanks. Can you describe what you're trying to demonstrate with the lines?
I'm illustrating the rear differential pinion angle. The red line shows where the pinion angle was pointing before the shop adjusted it. The angle was too steep causing vibrations. On a standard driveshaft configuration the pinion angle should be proportional to the angle of the transfer case output shaft. In other words if you draw a line coming from each end, they should be as close to parallel as possible as depicted in the green lines. Well, at least that is according to the information I found on the internet. I also watched several YouTube videos on the subject which now makes me an expert!
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Old 03-03-2019, 12:43 AM   #13
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Ah ha, now I see, said the blind man.
Thanks.
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Old 03-03-2019, 10:13 AM   #14
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Ah ha, now I see, said the blind man.
Thanks.
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Old 03-04-2019, 07:26 PM   #15
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If you go to SYE and CV you will need to change the rear angle back to what it was (pointed at the transfer case joint) but that should eliminate the vibration.
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Old 03-05-2019, 06:37 PM
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If you go to SYE and CV you will need to change the rear angle back to what it was (pointed at the transfer case joint) but that should eliminate the vibration.
I figured that. I will hold off on the SYE/CV a little longer. Need air conditioner.
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Old 03-05-2019, 06:45 PM   #17
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Is your front shaft spinning all the time now due to the locker? I did the one piece shaft swap when I regeared and my front shaft was out of balance.
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Old 03-05-2019, 09:12 PM
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If you go to SYE and CV you will need to change the rear angle back to what it was (pointed at the transfer case joint) but that should eliminate the vibration.
As far as I know the front driveshaft always spins but I may be wrong. I installed a Truetrac, which is a limited slip differential but since the front axle is disconnected when on 2H the LSD is invisible.

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