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Can't cure this vibration

fonzi03

NAXJA Forum User
Location
Az
01 XJ 4x4 195k
Rough Country 4.5" lift
15" alloy wheels 32" tires
Fixed length extended lower control arms

I have replaced
Steering gear box
All tie rods
All 4 balls joints with Moog
Hubs with Chrysler OE parts
Axle shaft u-joints Spicer
Rear driveshaft u-joints Spicer
Sway bar bushings frame and end links Moog
Upper control arm axle side bushings
Track bar
Track bar bracket new one welded on axle side


The truck vibrates between 60-70 on the highway and I just can't figure it out, all above parts were worn and needed replacing but I'm at a loss as to what's left. I have run with just the rear driveshaft and it still had vibes, swapped to just the front still had vibes. At this point I'm thinking possibly front axleshaft bearings but only because that's all that's left, I'm at a loss.











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When is the last time you checked and lubricated the slip yoke?
 
SYE or not ?

High pinion or low pinion Dana 30 ?

A vibe that is speed specific, typically appearing at about 55-60, and then disappearing at about 65-70 is almost always a rim issue, or a tire balance issue. Find a local independent tire shop with a Hunter Road Force Balance machine and some tire techs with gray hair.
 
Forgot to mention I have swapped rims/tires from my other xj and it did not cure so swapped back due to them rubbing like crazy being too big.

I plan to swap lower control arms with my other adjustable ones, swap my OME lift (coils, spacers, shocks and leafs) this weekend. Then my other wheels/tires.

No SYE, I have lubed the rear shaft and also greased the front shaft.

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if it isn't a tire/rim issue, it can still be a drum/brake/hub issue, or even a bent axle flange.

but no SYE, I'm betting the pinion angle has a part in this.

Rear d/s only and still having it eliminates the front for the most part.
 
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High pinion or low pinion Dana 30 ?

If not rims/tires/driveshafts, all that remains is driveline angles. With 4.5 inches of lift it should have an SYE.
 
Not sure on the high or low pinion I'll check when I get home.

If it needed a SYE wouldn't removing the rear shaft cure the issue?

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Not sure on the high or low pinion I'll check when I get home.

If it needed a SYE wouldn't removing the rear shaft cure the issue?

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You would think, but people talk about needing a SYE on 3"-3.5" lifts I'm surprised you would be able to get away without one on 4.5". Maybe experiment with a TCase drop and see if that helps at all (but again if you do a 1" drop you are equivalent to a 3.5" lift so it still may not completely solve it) .
 
Another possibility is the torque converter clutch. Next time on the highway and the vibration is there, keep your foot on the gas but with your other barely tap the brakes to trip the brake switch. That should kick the clutch off and you should see a rise in rpm. See if the vibration changes or goes away.
 
My point about the SYE is that with the rear driveshaft removed there would be no need for an SYE as the driveline angle of the rear shaft no longer exists.

I will try the brakes while on gas at highway speeds next time I'm in the vehicle however it's not an RPM related issue it is speed specific which should rule out the torque converter.

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It does have a 1" tcase drop which I forgot to mention as well by the way.

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You may have found the limit that an 2001 XJ can be lifted without spending a bunch of money on it.
There is a good chance the reason why you can remove either shaft is that both the driveshafts are vibrating, due to incorrect pinion and u-joint angles
.
97+ XJs start needing an SYE and shims at 3" and up, a transfer case drop is appropriate for less lift and, as you drop case the case more, the front pinion angle increases.

The front pinion angle increases as the lift goes up. The FSM call for 1 degree or less of front pinion angle, to avoid vibrations.
Your '01 came with a low pinion D30, which has little available Factory caster adjustment at the stock ride height.
This is one reason why adjustable control arms are needed for taller lifts.

As you lift an XJ, the caster decreases and the pinion angle increases.
At 4-1/2" of lift, the fixed control arms do not have a sufficient range of adjustment available, in the Factory shim pack, to adjust the front end so the pinion angle is with a 1 degree and still have enough caster.
Even with adjustable control arms, if the front pinion angle gets much over 1-2 degrees, you will feel vibs in your feet at, freeway speeds. It's hard on the u-joint and pinion bearings.
If you regear, the vibs will start at lower road speeds.
It became an issue when I regeared from 4.11 to 4.56, the vibs started 60 mph, where it to used to be smooth until about 80 MPH.

With a LP D30, at 4-1/2", once the pinion angle is adequate, there will be little caster, probably 3 degrees or less. It will be less stable at speed and will not return to center as easily.
Welcome to the limitations of the lifted LP-D30. Your choices are to change the front axle, rotate the Cs or to deal with it.

My 2001, at 4" has about 4-1/2 degrees of caster, using offset ball joints.
It also has drop brackets which significantly improve control arm angles and the ride quality. Someday, when the LP D30 wears out or breaks, a high pinion axle will replace it.
 
So rear angles can be fixed with a SYE but front angles can't really be fixed?

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I have about 6" of lift on my 2000 with a HD SYE kit. No issues in the front or rear, I do run 3* of caster(been that way for 16yrs) with no problem!
 
If it needed a SYE wouldn't removing the rear shaft cure the issue?

Lazyxj nailed it, both axles likely have extreme driveline to pinion angles. A T-Case drop increases the front driveline to pinion angle. A high pinion a D30 will help reduce the pinion angle, but with +4 inches of lift you still end up with less than ideal pinion angle and less than ideal caster.

My 2000 has 5.5 inches of lft with a swapped in HP D30, a HD SYE, and control arm drop brackets. My 98 has a 3 inches of lift, no SYE yet, and driveline vibes. Some 2000-01 had driveline vibes when brand new.
 
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So rear angles can be fixed with a SYE but front angles can't really be fixed?

No with adjustable CAs, the pinion angle can be set but the caster will be very low, much less than the specified 5 to 8-1/2 degrees.
A LP D30 would improve things, as well as cutting and rotating the Cs.
https://www.naxja.org/forum/showthread.php?t=1144315

To get enough caster with a LP D30, I had to lose a little lift and install offset ball joints.
 
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Jack it up and run it in D (on jackstands, obviously) to see if there's runout on the tires. Could be a bent drive flange or hub.

I've also been able to pinpoint sources by leaning forward/backwards/left/right while driving to see if the vibration feels/sounds louder.
 
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