Vibration at 70 mph

Thunderhead

Thunderhead

All graves go unvisited in time
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Just got an alignment done.
Drives strait and handles great until I hit 68-70 mph.
Then major vibs set in
3 inch lift on brand new 33’s
Before pulling F/R DS can anyone diagnose the alignment sheet?
Edit
Tom Wood rear CV
DA uppers and lowers
51D93183-9012-4B50-AF38-0D346F563C4F.png
 
Did you have vibs before the new tires?
 
Your front caster should be 4* or more. Your rear axle isn't square. The thrust angle is too high and your toe on the left rear is too much. All that shouldn't cause a vibe though, so I think some more pinion angle adjusting needs done. Another thing you could do to isolate which DS is the culprit would be to jack the rear end on jack stands and run it up to speed. That will eliminate the front DS.

To get the rear axle square to the frame, take a 4' level or straight edge place one end against the axle tube where the lower control arm bracket is, then the other end to the center t-case skid plate bolt head. A carpenter's square will help with this alignment. Measure both sides and see where you're at.
 
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The more I think about it, if your rear axle is out of square enough, it could make your rear drive shaft not so happy since the yoke will be cocked at an angle. Something to think about before you go cranking on those control arms.
 
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Do you have an angle finder? If so, what are your current F/R pinion and DS angles?
 
Do you have adjustable control arms and cv rear drive shaft?
I run a 4 " lift with 5.5 degrees of caster and have no vibes in the front. With a 3" lift you could probably run 5.5-6.0 degrees of caster and be fine.
Your running 2.9-3.2 degrees which is going to pitch your front pinion angle too high. which could cause some vibes.
You can get you rear thrust angle in with and adjustable rear track bar, and even though the rear toe is not adjustable on jeeps, you could get it within spec with adjustable control arms in the rear. Basically your rear axle is not squared up in the rear.
You will also want to check your rear pinion angle.


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williambmac said:
Do you have adjustable control arms and cv rear drive shaft?
I run a 4 " lift with 5.5 degrees of caster and have no vibes in the front. With a 3" lift you could probably run 5.5-6.0 degrees of caster and be fine.
Your running 2.9-3.2 degrees which is going to pitch your front pinion angle too high. which could cause some vibes.
You can get you rear thrust angle in with and adjustable rear track bar, and even though the rear toe is not adjustable on jeeps, you could get it within spec with adjustable control arms in the rear. Basically your rear axle is not squared up in the rear.
You will also want to check your rear pinion angle.


View attachment 189240
Click to expand...
Thanks, yea i have JKS front and rear TB
Savvy DA CA, Tom Wood CV shaft
 
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Thunderhead said:
Thanks, yea i have JKS front and rear TB
Savvy DA CA, Tom Wood CV shaft
Click to expand...


You need to either lengthen your front lowers or shorten you front upper to bring the caster to about 5.5.
How did it steer on the road? with caster @ 3.0 degrees your steering should feel pretty funky.
If you wanna drive out to NJ, I'll be happy to set it up on my alignment rack.
 
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You'd be hard pressed to find an alignment shop that is going to take the time to adjust the control arms to change the caster, unless he pays for the extra time to do so.
 
bobthetj03 said:
You'd be hard pressed to find an alignment shop that is going to take the time to adjust the control arms to change the caster, unless he pays for the extra time to do so.
Click to expand...

I wouldnt expect anything less. If I set a vehicle up on the alignment rack and the rear axle needs shims or the front needs cams or the struts opened up, we inform the customer and advise of the extra labor involved.
No one is gonna do it for free.
 
williambmac said:
I wouldnt expect anything less. If I set a vehicle up on the alignment rack and the rear axle needs shims or the front needs cams or the struts opened up, we inform the customer and advise of the extra labor involved.
No one is gonna do it for free.
Click to expand...
Yea it was Les Swab a west coast shop. I’m going to go back in and see if they can adjust more in depth. I think they just set the tow for the basic $89 alignment. They are supposed to be customer based and have more options on alignments so we will see how it goes
 
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