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RE 3.5' lift vibes

alexgalexg

NAXJA Forum User
Location
Connecticut
98 XJ 4.0 automatic 4wd
Currently have the front drive shaft in the rear while waiting on custom shaft.

No vibes at any speed (tested up to 85). However downhill if I let off the gas I get a slight vibe/grind noise for about one second.

My lift contains RE full leafs, monotube shocks, springs and sway bar disconnects, control arms, iro track bar and Adam's slip yoke eliminator.

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When you let off on the gas, your axle will rotate slightly from less torque applied to it; affecting your pinion angles a little. Most of the time, it's a non issue.

What is the condition of the driveshaft you're now using? High mileage u-joints? Condition of center-ball in CV joint? Perhaps that is contributing to the noise. Also remember, that it was used in the front, with probably a slightly different operating angle that the current u-joints have been worn into.

Since it's only making noise on downhills / foot the gas situations; I suggest you wait and see what happens when you install your new rear driveshaft. The noise may go away on its own.

I'd be happy with no vibes up to 85 mph, but then I'd be afraid to push my XJ up to 85 mph.
 
I think Ivan is on the right track regarding the change in pinion angle.

Out of curiosity, what shackles are you running? Any shims in place yet?

If you're still running stock shackles, bear in mind that they're far too short to get good articulation (or really decent ride quality) out of those leaf packs. I went with JKS Boomerangs, which partially corrected my pinion angle, and then finished it off with 2.5° shims (if memory serves me correctly).
 
Get the driveshaft angles taken care of now while your waiting for the new shaft!
 
Oem shackles. And it is a drive shaft with 204k on it. I did however give it a good twist and it has no play so it seems to be in good shape. No sparrows chirp either. I'm sure it's the angles. I do intend to run the regular shackles for now I only have so much budget but I could play with the angles

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Factory angles usually don't work for a cv shaft.
http://4xshaft.com/driveline101.asp
Front angles are changed due to control arms. Should be good but I won't know until my new stuff comes in. I can definitely see the back needing adjusting although I dont get vibes other than when I go down hill for about 1 sec after letting off gas so it's definitely not too bad

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Front doesn't matter, but you should have waited on ordering a rear shaft until after you shimmed/shackled it and re-adjusted your front to compensate. By the time you get the drive shaft angles figured out you maybe 3/8"-1/2" higher.
 
Front doesn't matter, but you should have waited on ordering a rear shaft until after you shimmed/shackled it and re-adjusted your front to compensate. By the time you get the drive shaft angles figured out you maybe 3/8"-1/2" higher.
I thought the sye would compensate. I didnt know I would need to do anything else. I dont even know what I need to do. I'll have to research tomorrow

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The rear axle needs to be shimmed (between spring perch and spring) to get the pinion in line with the driveshaft when using a CV style shaft. Ideally I shoot for the pinion to be about 2 degrees down from the shaft so when the pinion rotates up under load it helps keep it in line. You can get a cheap angle finder and need to measure the shaft and the pinion. Lots more info out there on how to do it. My guess is your pinion is too low now.
 
Alright thanks folks I'll take a look tomorrow. I see that iron rock sells a set of shims. Annoyingly unpainted but itll have to do

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Need to check for vertical movement in the CV shaft. Will indicate a worn centering bearing and yoke.

Also need to shim to point pinion at the case, as others mentioned

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Need to check for vertical movement in the CV shaft. Will indicate a worn centering bearing and yoke.

Also need to shim to point pinion at the case, as others mentioned

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No play anyplace. I am looking into shims

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So I ordered an angle finder. I set it to zero on a flat part of the yoke coming out of the rear axle. I then set it on the drive shaft and measured roughly an 8.5 degree difference. That seems like a lot for a 3.5 lift. People with the same lift said they needed a 3 degree shim. Did I do this wrong? Or do I really need that big of a shim

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#1, measure off the back of the diff for angles. You may be be seeing slop in the yoke, so I would only use the "mid-shaft" angle. You should see repeatable angles though!
 
Btw, terrain makes absolutely no difference, just make sure you don't hit "re-set" between readings.
 
#1, measure off the back of the diff for angles. You may be be seeing slop in the yoke, so I would only use the "mid-shaft" angle. You should see repeatable angles though!
Back of the diff? Like where the cover bolts on?
I so gave it a firm tug and got no play but I will still take your advice. My friend said something about spring wrap being a possible culprit. But deal, tomorrow morning before work I'll set to zero on the back of the diff and measure mid drive shaft for numbers. I'll repeat it tomorrow night after work to see if there is a change in measurement

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On either side of the cover is a "flat" machined area. No such thing as spring wrap with RE springs (unless you have the axle tied to a tree).
 
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