Shimmy at 65mph in a 2006 LJ

[AndyG]

First thing is swap tires front to back. May be a failing tire-

Then pull the front shaft -

Also are your front upper control arm bushings stock at the axle- those can allow movement more than I realized.

 

[Sensei]

Core4x4 and regular bushings but the ones on the axle is believe are still stock.

Here's the amount of movement I've got. I think that's normal on this side but the axle side is the same amount with old bushings. I think those did get replaced.

https://photos.app.goo.gl/XcPd7w7fCjCF4dLJ7

This side to side movement isn't really a concern. It's just the rubber in the bushing flexing as you pry. The control arms don't control the lateral position of the axle anyways, the trackbar does that. Control arms control the medial position, ie forward and back. If you feel a consistent thumping or shaking at 60 mph, I would consider that a "vibe", most likely attributed to the driveline like others have said. Can you post a picture of your rear axle, pinion angles, etc.

 

[catbones2010]

First thing is swap tires front to back. May be a failing tire-

Then pull the front shaft -

Also are your front upper control arm bushings stock at the axle- those can allow movement more than I realized.

Hey Andy,

Thank you in advance in helping

So far I've gone through tires, wheels balancing and rotation. I've replaced ball joints, tie rods, hubs, axle ujoints and control bar. Even pulled the stock cam bolts and put in deletes so I'm sure I'm not 100 percent on caster here.

Before I did all that replacement of ball joints etc.. the first thing I pulled was the front DS. It didn't make the shimmy go away but made it defined more.

I believe this has to do with something front axle or driveshaft or something because when I did use the factory caster bolts and adjusted the caster from 6 to 7 or 5.5 even, the speed the shimmy would start and stop would change. 6 caster was at 57-62 and 7 caster was at 55-60. Now without the cam bolts in there it's at 62-66 so I'm sure my caster is at 5 or 4. I need to adjust caster.

So whatever is doing it, must be upfront somewhere. Removing rear DS makes it all go away. So I think what's happening is without the rear DS in, things get mushed forward a little and it deletes the shimmy. Why we are thinking upper control arm bushings.

 

[catbones2010]

This side to side movement isn't really a concern. It's just the rubber in the bushing flexing as you pry. The control arms don't control the lateral position of the axle anyways, the trackbar does that. Control arms control the medial position, ie forward and back. If you feel a consistent thumping or shaking at 60 mph, I would consider that a "vibe", most likely attributed to the driveline like others have said. Can you post a picture of your rear axle, pinion angles, etc.

I'll grab a pic but it's conventional so my output shaft matches the pinion angle when I measure it.

The front UCA bushings are still stock, FYI. Control arms are adjustable from Core4x4 with their bushings, what's in video flexing. The lower control arms same brand and bushing but no flex. I'm guessing it's just the way the uppers are positioned at the frame where I get the flex. I also don't know if there is any forward backwards motion from uppers unless there is and they are silent.

 

[catbones2010]

Hey Andy,

Thank you in advance in helping

So far I've gone through tires, wheels balancing and rotation. I've replaced ball joints, tie rods, hubs, axle ujoints and control bar. Even pulled the stock cam bolts and put in deletes so I'm sure I'm not 100 percent on caster here.

Before I did all that replacement of ball joints etc.. the first thing I pulled was the front DS. It didn't make the shimmy go away but made it defined more.

I believe this has to do with something front axle or driveshaft or something because when I did use the factory caster bolts and adjusted the caster from 6 to 7 or 5.5 even, the speed the shimmy would start and stop would change. 6 caster was at 57-62 and 7 caster was at 55-60. Now without the cam bolts in there it's at 62-66 so I'm sure my caster is at 5 or 4. I need to adjust caster.

So whatever is doing it, must be upfront somewhere. Removing rear DS makes it all go away. So I think what's happening is without the rear DS in, things get mushed forward a little and it deletes the shimmy. Why we are thinking upper control arm bushings.

Also to add to the above, if I wasn't adjusting the caster more or less, before all the ball joint, hubs change... tire pressure of the front tires, 2-3 psi would also move it when it would happen, start and end.

So now with new ball joints, hubs... It's either my alignment caster and front DS angle or maybe my front DS just can't handle the rpms with 5.13s as the DS front and rear is still stock.

 

[Sensei]

I'll grab a pic but it's conventional so my output shaft matches the pinion angle when I measure it.

The front UCA bushings are still stock, FYI. Control arms are adjustable from Core4x4 with their bushings, what's in video flexing. The lower control arms same brand and bushing but no flex. I'm guessing it's just the way the uppers are positioned at the frame where I get the flex. I also don't know if there is any forward backwards motion from uppers unless there is and they are silent.

Typically I try to get the pinion at -1 degree, and not directly at the tcase. Just a personal preference. Might be worth giving it a shot.

 

[catbones2010]

Typically I try to get the pinion at -1 degree, and not directly at the tcase. Just a personal preference. Might be worth giving it a shot.

That would be for SYE setup tho

 

[catbones2010]

This side to side movement isn't really a concern. It's just the rubber in the bushing flexing as you pry. The control arms don't control the lateral position of the axle anyways, the trackbar does that. Control arms control the medial position, ie forward and back. If you feel a consistent thumping or shaking at 60 mph, I would consider that a "vibe", most likely attributed to the driveline like others have said. Can you post a picture of your rear axle, pinion angles, etc.

Here's a photo for you of the rear

 

[Sensei]

Here's a photo for you of the rear

View attachment 574727

Seems a little greasy back there. Is that oil fresh? Pinion angle looks okay, maybe slightly high without sye. Id try lengthening the lower arms slightly to bring the angle down.

 

[catbones2010]

Seems a little greasy back there. Is that oil fresh? Pinion angle looks okay, maybe slightly high without sye. Id try lengthening the lower arms slightly to bring the angle down.

I'm on the north east so that all fluid film for winter

 

[catbones2010]

Seems a little greasy back there. Is that oil fresh? Pinion angle looks okay, maybe slightly high without sye. Id try lengthening the lower arms slightly to bring the angle down.

I might just get a new driveshaft, i don't like how it feels and vibrates and I'm not very positive on my ujoint work lol so that might get replaced, also the fact that stock is not balanced for 3500+ rpms that I'm spinning her at with 5.13 gears and 33s. 35 inch tires would probably help but that another 30k or so away.

 

[AndyG]

Hey Andy,

Thank you in advance in helping

So far I've gone through tires, wheels balancing and rotation. I've replaced ball joints, tie rods, hubs, axle ujoints and control bar. Even pulled the stock cam bolts and put in deletes so I'm sure I'm not 100 percent on caster here.

Before I did all that replacement of ball joints etc.. the first thing I pulled was the front DS. It didn't make the shimmy go away but made it defined more.

I believe this has to do with something front axle or driveshaft or something because when I did use the factory caster bolts and adjusted the caster from 6 to 7 or 5.5 even, the speed the shimmy would start and stop would change. 6 caster was at 57-62 and 7 caster was at 55-60. Now without the cam bolts in there it's at 62-66 so I'm sure my caster is at 5 or 4. I need to adjust caster.

So whatever is doing it, must be upfront somewhere. Removing rear DS makes it all go away. So I think what's happening is without the rear DS in, things get mushed forward a little and it deletes the shimmy. Why we are thinking upper control arm bushings.

Have you replaced the 2 upper stock control arm bushings in the front axle- - those have a big hand in axle stability. Don’t underestimate them.

The fact that caster changes move it around points to a shaft vibe- but the fact pulling the shaft made it more defined rules that out.

Don’t rule out motor and transmission mounts and cracked control arm brackets as well. Be aggressive and persistent and you will get it.

Love to hear more, keep us posted.

 

[catbones2010]

Have you replaced the 2 upper stock control arm bushings in the front axle- - those have a big hand in axle stability. Don’t underestimate them.

The fact that caster changes move it around points to a shaft vibe- but the fact pulling the shaft made it more defined rules that out.

Don’t rule out motor and transmission mounts and cracked control arm brackets as well. Be aggressive and persistent and you will get it.

Love to hear more, keep us posted.

I think I will start with replacing the upper control arm bushings on the axle and see what Core4x4 says about the play on their bushings. I'll also get my caster set to 5 degree on driver side and 5.5 on passenger. Including toe in. See how that works out and look over anything in terms of brackets. I feel like I should replace my stock driveshaft just to get a better balanced one for the high rpms. I think that would be a good choice. I'll also drop the rear pinion by a degree to see if it helps. Unless you think that's unnecessary from the driveshaft photo.

 

[AndyG]

I think I will start with replacing the upper control arm bushings on the axle and see what Core4x4 says about the play on their bushings. I'll also get my caster set to 5 degree on driver side and 5.5 on passenger. Including toe in. See how that works out and look over anything in terms of brackets. I feel like I should replace my stock driveshaft just to get a better balanced one for the high rpms. I think that would be a good choice. I'll also drop the rear pinion by a degree to see if it helps. Unless you think that's unnecessary from the driveshaft photo.

View attachment 574785

The Rock Jock tombstone kit is excellent but just new bushings may take care of it. Jeep looks well cared for and in good shape for the north east.

Trick is not to mangle the passenger side bracket- it is heavy sheet metal basically.

 

[topfuel83]

It's hard to tell from your picture, but it almost looks like your rear driveshaft angles are off. Without a SYE and CV joint, both of the yokes need to be at the same angle to cancel each other's angular momentum. If you draw an imaginary straight line from the centerlines of the rear axle yoke and the t-case yoke, they need to parallel to each other. If the yokes on your rear driveshaft are at different angles, you will get vibrations. Buy a digital angle finder and you can check angles very easily. Klein makes an inexpensive one with magnets.

 

[AndyG]

It's hard to tell from your picture, but it almost looks like your rear driveshaft angles are off. Without a SYE and CV joint, both of the yokes need to be at the same angle to cancel each other's angular momentum. If you draw an imaginary straight line from the centerlines of the rear axle yoke and the t-case yoke, they need to parallel to each other. If the yokes on your rear driveshaft are at different angles, you will get vibrations. Buy a digital angle finder and you can check angles very easily. Klein makes an inexpensive one with magnets.

Good post - he is close to being in double cardan rear shaft territory - normally you are with the pinion pointed in line.

The perfect shaft angle is the one that does not vibrate or growl. Pros will try 50-60 settings to find the sweet spot.

My LJR hardtop changes my rear pinion angle enough to make it sing some.