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4WD and 4 Auto vibration and thrum. Your thoughts Needed

drvn

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Hey everyone
Just wanted a group consensus if I'm being a wuss or if I need to take her in.
I've noticed over the last couple weeks that when I'm driving in 4 Auto or 4 High there are few things which I hadn't notice before.
(2020 JLU & haven't used these much yet). Obviously, I had 4 High with my prior JK but got the 4 Auto option for the new one and didnt appreciate this feel on the JK.

Anyways...
-Mild jerkiness mph 15-30

-A mild but continuous vibration felt in the floor and gas pedal at all speeds. Mild improvement with coasting.

-A continuous audible thrum.

*EDIT* The vibration and sound both get worse with higher speeds particularly over 50 mph.

Both go away immediate when shifting back into 2WD

Can't say I notice either of these in my F150 or Tacoma in 4 Auto and 4 High.

Anyone else have this experience? Causes?

Many thanks!
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aldo98229

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Mine doesn’t do it. I have Selec-Trac as well.

Sounds like your front driveshaft that is out of balance. But it seems strange that you only feel it within a lower speed range. Normally an off-balance driveshaft would vibrate more the faster it rotates.

Have you noticed if the vibration goes away when you release the load off the front axle —i.e., coasting?

These vehicles also have an automatic front axle disconnect, which JK didn’t have. I wonder if that could be causing the vibration.
 

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Hey everyone
Just wanted a group consensus if I'm being a wuss or if I need to take her in.
I've noticed over the last couple weeks that when I'm driving in 4 Auto or 4 High there are few things which I hadn't notice before.
(2020 JLU & haven't used these much yet). Obviously, I had 4 High with my prior JK but got the 4 Auto option for the new one and didnt appreciate this feel on the JK.

Anyways...
Mild jerkiness mph 15-30 then goes away
A mild but continuous vibration felt in the floor and gas pedal.
A continuous audible thrum.

Both go away immediate when shifting back into 2WD

Can't say I notice either of these in my F150 or Tacoma in 4 Auto and 4 High.

Anyone else have this experience? Causes?

Many thanks!
Big difference between 4 auto and 4hi, which are you referring to specifically?
 
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drvn

drvn

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Black Jeep Convertible

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I initially noticed in 4 Auto. So then I put in 4 High....and the experience was similiar.
If it's happening in 4hi in a straight line then definitely take it in. If not easily replicated, record a video for them.
 

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drvn

drvn

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Mine doesn’t do it. I have Selec-Trac as well.

Sounds like your front driveshaft that is out of balance. But it seems strange that you only feel it within a lower speed range. Normally an off-balance driveshaft would vibrate more the faster it rotates.

Have you noticed if the vibration goes away when you release the load off the front axle —i.e., coasting?

These vehicles also have an automatic front axle disconnect, which JK didn’t have. I wonder if that could be causing the vibration.
Thank you greatly for the reply.
I took it out again for clarification. The vibration and sound both get worse with higher speeds particularly over 50 mph. Maybe a little improvement with coasting.
 

aldo98229

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The fact that it only occurs in 4A and 4H strongly suggests that it has to do with the front driveshaft; the rear driveshaft is always turning, the front only spins in 4WD.

I doubt it is the front axle. Unlike driveshafts, axles are always spinning, so the front axle wouldn’t be affected when 4WD is engaged.

A vibration that increases with vehicle speed and dissipates when you lighten the load sounds a lot like a driveshaft that has gone off balance.

Driveshafts come from the factory perfectly balanced with these tiny weights; much like a wheel. But weights can come off for a variety of reasons; it could be a factory defect, or they can come off when you hit a rock on the trail. Another possibility is that the front driveshaft is slightly bent.

Assuming it is the front driveshaft: if it was damaged on the trail/under use, the warranty is not going to cover it; that would be due to “misuse.” If you haven’t taken the Jeep off-road, or damaged the driveshaft by hitting a high curb or something like that, then it came defective from the factory and should be replaced under warranty. Either way, the dealer should be able to determine by putting the Jeep on the lift, if the driveshaft lost its balance on its own, or due to a severe blow.

If you have to pay for the repair yourself, it may cost about the same to replace the driveshaft than to have it rebalanced. In which case, I wouldn’t have the dealer do it. An independent shop is going to charge you a lot less in labor. Last time I checked, a new driveshaft was $1,000 + labor.

Keep us posted how things go.

Good luck.
 

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Hey everyone
Just wanted a group consensus if I'm being a wuss or if I need to take her in.
I've noticed over the last couple weeks that when I'm driving in 4 Auto or 4 High there are few things which I hadn't notice before.
(2020 JLU & haven't used these much yet). Obviously, I had 4 High with my prior JK but got the 4 Auto option for the new one and didnt appreciate this feel on the JK.

Anyways...
-Mild jerkiness mph 15-30

-A mild but continuous vibration felt in the floor and gas pedal at all speeds. Mild improvement with coasting.

-A continuous audible thrum.

*EDIT* The vibration and sound both get worse with higher speeds particularly over 50 mph.

Both go away immediate when shifting back into 2WD

Can't say I notice either of these in my F150 or Tacoma in 4 Auto and 4 High.

Anyone else have this experience? Causes?

Many thanks!
I see that you're on a 3" lift with geometry brackets. Unlike fully adjustable control arms, the brackets just give whatever they give as far as caster correction. To much caster will also come with too much pinion angle. Too much pinion angle causes the driveshaft to repeatedly speed up and slow down during every rotation, causing a whip affect, which translates to a vibration that will get worse as vehicle speed increases.
 
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drvn

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I see that you're on a 3" lift with geometry brackets. Unlike fully adjustable control arms, the brackets just give whatever they give as far as caster correction. To much caster will also come with too much pinion angle. Too much pinion angle causes the driveshaft to repeatedly speed up and slow down during every rotation, causing a whip affect, which translates to a vibration that will get worse as vehicle speed increases.
I did get synergy adjustable lower control arms. The caster is 6.5 drivers side and 6.9 passengers side. Too much??
 

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I did get synergy adjustable lower control arms. The caster is 6.5 drivers side and 6.9 passengers side. Too much??
No, not too much. You're in the sweet spot with caster. Just trying to run the process of elimination. I'm still hung up on it being driveshaft related. Even with a happy caster, the 3" lift still made a height differential between both ends that could still lead to the condition I described earlier.

If safety precautions are used, you could put the Jeep up on jack stands under the axles and see what the driveshaft is doing.

When I pulled the 2" Dynatrac to make way for the 3.5" MC, I also did a front driveshaft to avoid contact between it and the crossmember nearest the t-case end. Lately, more installers are starting to recommend at least a new front driveshaft on 2.5", rather than just for 3.5" and up.
 

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Wow. That’s bad news if you can’t rebuild the clutch packs on JL’s Selec-Trac/MP3022
 

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I doubt it has anything to do with being unable to rebuild anything.

It is usually more cost-effective for FCA to swap defective parts on vehicles under warranty than to pay the dealer to rebuild them.

The rear locker on my 2009 JKR broke while still under warranty. FCA had the dealer swap the entire rear axle. It was cheaper to do that than to open the differential, figure out what had happened, rebuild it and put it back together.

FCA then had the dealer ship my original axle to Michigan to analyze what went wrong.

I suspect they will do the same with the OP’s transfer case.
 
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drvn

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Update: transfer case binding (thought to be secondary to 3" lift)
I was told driveshaft angle is 10 degrees rather than 3 degrees.

What is the best way to remedy this??

A New driveshaft that is longer?

Anything else?

Thanks!

@Black Jeep Convertible @aldo98229 @Headbarcode @Notorious
 

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Update: transfer case binding (thought to be secondary to 3" lift)
I was told driveshaft angle is 10 degrees rather than 3 degrees.

What is the best way to remedy this??

A New driveshaft that is longer?

Anything else?

Thanks!

@Black Jeep Convertible @aldo98229 @Headbarcode @Notorious
Go to JE Reels driveline website. Click the menu button, tech info in the drop down, and read through the vibration issues section. Angles are explained in the torsional vibration part.

Very good read from a great company, and I'd rather point you to the source of info rather than risk leaving something out in my own version.

Hopefully this can help you out some.
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