Getting Vibes over 60 MPH....

Hello,
So right now I'm experiencing vibes once I hit about 60 mph, nothing below that. I just did I bunch of work to this jeep, some of which I'll list below.

Modifications: (2000 Jeep Cherokee)
-3.5" OME Lift
-31x10.5 tires
-4 degree rear shims
-1" T-Case drop
-SYE
-New double cardan REAR shaft
-Rebuilt FRONT shaft

That's all I can think of as far as mods that matter in this case. Any ideas are greatly appreciated. Thanks!

speed-specific vibrations tend to indicate wheel balance. can you tell if it is front or rear of vehicle?
are they new tires? swap your tires front to rear and see if anything changes.
start simple, you made alot of changes and you need to use the process of elimination.

sidriptide said:

speed-specific vibrations tend to indicate wheel balance. can you tell if it is front or rear of vehicle?
are they new tires? swap your tires front to rear and see if anything changes.
start simple, you made alot of changes and you need to use the process of elimination.

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Thats the truth.

I didn't see anything about an adjustable track bar. If your problem persists after rotating the tires, that would be my next guess.........aligning the front axle back under the jeep.

It's really hard to tell where the vibes are coming from. The tires and wheels are all brand new and I just had it aligned less than 50 miles ago. You are also correct about having the adjustable track bar. I noticed that it pulls to the left today, so I'm headed back in to the alignment shop again....

If this doesn't help I'll be pulling the front DS today and doing a little testing

Would the 1" T-Case drop bracket play a role in this?

I'm wondering if your rear driveshaft is properly aligned. With a SYE and CV shaft, the rear axle pinion should point at, or slightly below the transfer case output. What makes me wonder is that you have both an SYE AND a T-case drop. With the SYE you shouldn't need the t-case drop.

What is you operating angle at the pinion? If you can't tell me that, then you need to find out.

Driveshaft vibes, in my experience, show up mostly as you accelerate from 30 and again, slightly, around 60+.
Tires very typically show up at 60, across all makes / models that I've seen. Don't know why, just do.
Try rotating tires. I know they are new, and you don't think they should be the problem, but they still might be and it's free to rotate.

just pointing out some things (some of which might already be mentioned)

escout said:

-3.5" OME Lift
-31x10.5 tires

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was the lift/tires just installed? have you had it aligned? what is castor/front pinion angle at? are the tires balanced?

escout said:

-4 degree rear shims

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what is the pinion angle at compared to the shaft and the output of the Tcase?

escout said:

-1" T-Case drop
-SYE
-New double cardan REAR shaft

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not that it will fix your issue... but why are you running a Tcase drop with the SYE?

escout said:

-Rebuilt FRONT shaft

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are you running this in the front or the rear? were you careful to ensure phase when you rebuilt it?

With all that you changed, it leaves a lot of possibilities to what could cause the vibration. My thoughts off the top of my head:

-Were the wheels and tires balanced once they were mounted together? I know, it sounds simple but I've known people who didn't realize new tires and wheels needed to be balanced.
-Are you running stock lower control arms? If so, you'll get vibes at 3.5" and that won't change until you get arms that fit the new height.
-If you did get new arms, the caster needs to be about 6 degrees, if that wasn't set when you got the alignment done, it could cause vibes.
-I've heard of people getting new driveshafts that came from the factory out of balance. If you eliminate everything else, you may have to get one of the shafts rebalanced.
-Can you feel the vibrations in the steering wheel significantly, or is it just the body in general? That can narrow down where you're looking.

WillXJ36 said:

-Are you running stock lower control arms? If so, you'll get vibes at 3.5" and that won't change until you get arms that fit the new height.

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a severe pinion angle can cause vibes. this can be remedied by dialing back castor. less castor will give you undesirable handling characteristics, but shouldnt cause vibes in its self. as for replacing stock arms to get rid of vibes... false. that is a pretty poor recommendation to make. they may limit droop but at 3.5" of lift the stock castor adjusters should be able to dial a comfortable ride with the stock arms. for example, my RE arms are the same length as stock eye to eye, just beefy and offset on the axle side.

So, I ended up pulling off the front driveshaft and boom! No more vibes. I took the front shaft in and had it rebuilt...Again. When I talked to the guy at the shop he said that a lot of times those splines in the center of the tube have a tendency to wear out and vibrations are amplified with lifted vehicles. Whatever the cause was in that shaft, it's fixed now. Just rolled 75mph down the interstate and was vibe free!

atriot:

Cool! I think that's where mine are coming from too... its very minor but have yet to pull it out and test it.