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1998 Jeep Cherokee xj sport w/4.0 auto D30 front and 8.25 rear 6” rubicon express lift fox shocks
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Discussion Starter · #1 ·
My name is Craig and I just finished putting my 98 Cherokee xj back together after a long 3 years of off and on work I installed a 6” rubicon express lift w/fox shocks a rear disc brake conversion(kit by LEED BRAKES) I also did axle seals, rear lower quarters, extended brake hoses from Rusty’s Offroad it also has a transfer case lowering kit and a kit for lifted cherokees for the power steering gear box that keeps it in place plus plenty of other things. My problem is when I drove it the other day I noticed a sort of what I can only describe as maybe grinding or vibration but when I let off the throttle it gets worse I’m stumped as to what it could be I do believe that the pinion angle is more then the 10 degrees recommended but that would be more a vibration then grinding if anyone can help me it would be appreciated.
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1998 Jeep Cherokee xj sport w/4.0 auto D30 front and 8.25 rear 6” rubicon express lift fox shocks
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19 Posts
Discussion Starter · #3 ·
Have yoiu checked your U joints? If you have one going south it might not like the new angle it has to accomodate
I haven’t checked it yet but I plan to but would it do what I described when I let off the throttle?
 

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any lift over 3" usually requires a Slip Yoke Eliminator (SYE) and a double cardan drive shaft (like on the front) with that lift you put the u-joints on some steep angles and cause major vibrations. Torque underload will minimize it, but when you let off the throttle and coast it takes the load off and will vibrate more.
 

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1998 Jeep Cherokee xj sport w/4.0 auto D30 front and 8.25 rear 6” rubicon express lift fox shocks
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19 Posts
Discussion Starter · #5 ·
any lift over 3" usually requires a Slip Yoke Eliminator (SYE) and a double cardan drive shaft (like on the front) with that lift you put the u-joints on some steep angles and cause major vibrations. Torque underload will minimize it, but when you let off the throttle and coast it takes the load off and will vibrate more.
It’s a 6” lift and pinion angles are off, I do get vibration at speed and it does seem to be more pronounced when I let off, I do have a transfer case drop but the new springs are sitting flat on the perches so I probably need wedges to re-angle the pinion any idea as to where I can get wedges for it?
 

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what You are looking for are pinion shims. But, you don't typically don't shim a pinion with a standard rear drive shaft. if you install a SYE and a double cardan drive shaft, then you shim the pinion to correct drive line angles.
Pinion shims
Line Font Rectangle Parallel Event
 

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1998 Jeep Cherokee xj sport w/4.0 auto D30 front and 8.25 rear 6” rubicon express lift fox shocks
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19 Posts
Discussion Starter · #7 ·
what You are looking for are pinion shims. But, you don't typically don't shim a pinion with a standard rear drive shaft. if you install a SYE and a double cardan drive shaft, then you shim the pinion to correct drive line angles.
Pinion shims View attachment 230496
Yea mine looks more like the top illustration although I haven’t checked the angle of degree I’m sure that’s the issue but I was told that I can’t use wedges because it’s a factory driveshaft and not a double cardan w/SYE set up
 

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1998 Jeep Cherokee xj sport w/4.0 auto D30 front and 8.25 rear 6” rubicon express lift fox shocks
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19 Posts
Discussion Starter · #8 ·
what You are looking for are pinion shims. But, you don't typically don't shim a pinion with a standard rear drive shaft. if you install a SYE and a double cardan drive shaft, then you shim the pinion to correct drive line angles.
Pinion shims View attachment 230496
How do I determine the degree of wedge I need to properly align the unjoints?
 

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typically, you use wedges to align the pinion to either point up or down, depending on your drive shaft setup. Here is the link to my XJ Hack n Tap SYE install. i used a protractor on the drive shaft and the rear diff cover. The difference is the angle in degrees. You don't have to worry about your whole jeep being level or anything, cause you are looking for the difference not anything specific, like from 90 degrees.
 

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Here is an excellent video that explains u-joint offset and what can cause vibrations
 

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1998 Jeep Cherokee xj sport w/4.0 auto D30 front and 8.25 rear 6” rubicon express lift fox shocks
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19 Posts
Discussion Starter · #11 ·
typically, you use wedges to align the pinion to either point up or down, depending on your drive shaft setup. Here is the link to my XJ Hack n Tap SYE install. i used a protractor on the drive shaft and the rear diff cover. The difference is the angle in degrees. You don't have to worry about your whole jeep being level or anything, cause you are looking for the difference not anything specific, like from 90 degrees.
Thank you for the info
 
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