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Installed shims, makes even more vibes now.

R

RSchurig356

NAXJA Forum User
Location
Michigan
Hello,

I have a 2000 XJ Classic. I recently installed a bastard pack setup that gave me roughly 2" of lift over stock. I also installed a set of V8 ZJ front coils to lift the front a bit, probably 1-1.5" lift. I was getting some vibes around 30 mph and up around 70 also. It was loud driving down the freeway at 75 or 80 mph.

I installed a set of 2 degree shims to try and settle down the vibes. After installing them, the vibe is worse at both of the speeds. Driving at 80 mph sounds like subwoofers going off in my Jeep. Its really annoying on a 600 mile long trip to listen to that. Anybody have any ideas whats wrong or what should I do to fix this? Where should I start looking? Thanks guys.
 
Which way did you install the shims - fat part to the front or fat part to the rear? You want to install them so that the pinion is parallel to the transfer case output. You also probably want to drop the transfer case an inch.
 
Installing shims on a driveline that has no SYE in it will cause vibrations. To warrant installing shims you need to have a SYE then you would install shims to point the pinion towards the output of the tcase. With regular slip yoke you want the output and pinion to be parallel.
 
dave92cherokee said:
Installing shims on a driveline that has no SYE in it will cause vibrations.
Click to expand...

This is not always true. The center pin of the rear leaf spring is not located in the middle of the spring, it is closer to the front of the spring than the rear. Because of this, when you lift the Jeep the angle of the pinion will increase; it will generally point higher as you lift more. If you want the Tcase output and pinion to be parallel then you have to lower the pinion angle slightly which is why you put the fat part of the shim in the front and the slim part to the rear.

dave92cherokee said:
With regular slip yoke you want the output and pinion to be parallel.
Click to expand...

This is correct. No argument here.
 
If you do not have a SYE installed then you may have made things worse.

If you don't have an SYE then you will need an angle finder to measure the angle of the transmission-transfer box. Also measure the pinion angle of the rear diff. The two must be within 3 degrees of each other with the pinion angle less than the trans angle. This allows the rear angle to increase due the spring wrap under acceleration/load.

Check this link out: http://jniolon.clubfte.com/drivelinephasing/drivelinephasing.html
 
I have a 2" lift on my '01. With a hack-n-tap style SYE i needed 5* shims to correct my driveline angles and vibes.....

Start with a transfer case drop and go from there. You very well may need an SYE now.
 
96+ XJs are much more sensitive to driveline vibes than the older models. I'd look at an SYE, hack and tap if you need to save money. That's what I did and have no regrets.
 
the_weirdo said:
This is not always true. The center pin of the rear leaf spring is not located in the middle of the spring, it is closer to the front of the spring than the rear. Because of this, when you lift the Jeep the angle of the pinion will increase; it will generally point higher as you lift more. If you want the Tcase output and pinion to be parallel then you have to lower the pinion angle slightly which is why you put the fat part of the shim in the front and the slim part to the rear.
Click to expand...

i have never heard of that. when i had my lift and no SYE i used shims with the fat part in the back, like they are supposed to be, to get my output and pinion parallel, or close to it.

to the OP, i would start suspecting u-joints
 
the_weirdo said:
This is not always true. The center pin of the rear leaf spring is not located in the middle of the spring, it is closer to the front of the spring than the rear. Because of this, when you lift the Jeep the angle of the pinion will increase; it will generally point higher as you lift more. If you want the Tcase output and pinion to be parallel then you have to lower the pinion angle slightly which is why you put the fat part of the shim in the front and the slim part to the rear.
Click to expand...


Thats going to depend greatly on how you lift. If you lift with a spring pack, which the OP did, then most likely he's going to need to RAISE the pinion. He would want to put the taller part in the back. IF he used some crazy 9 inch tall shackle with stock springs then he MIGHT need to lower the pinion and put the taller part in the front... but in the years that I've been doing this I've never seen one installed that way... Not that it's impossible but if that's the case I'd say you're doing something wrong.
 
I did install the shims with the thicker part in the rear. I was hoping that this would pitch the pinion up so that the angles would be close to parallel. I guess I ought to measure the angle and see how far I am off.

I suppose the next step is to take the shims back out. Assuming I take the shims out and my angle is off, how should i fix that? Will a transfer case drop cause problems by pitching the engine/transmission down?
 
measure, then determine what size shims you need. we cant recommend that the t-case drop will fix it or not because we dont know which way your pinion is off, too far up or down.
 
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