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IRO SYE vibes!!!

K

keep0njeepin0n

NAXJA Forum User
Location
Beaufort, SC
I had some vibes with full throttle from 30-35 and after 65 on the hwy. I did the IRO SYE today, and eliminated the T-case drop. Now, I still have the same vibes, plus some that feel even worse at about 50-60 and sometimes under hard acceleration it feels like something is thumping the bottom of my floorboard right under my left foot, on drivers side.

I have a 98 4.0 NP231, 8.25, AW4, and got with my kit a front DS from an AW4.


Anybody know what I could do? I've searched but it seems like there's a lot of different answers and not everything I read had the exact same problems as me.
 
Yes sorry forgot to mention all that info...It has a 3" procrap lift (installed by PO) and shims in the rear axle, and with the IRO SYE, it looks like the rear pinion is pointed directly at, if not a hair down from the rear DS....
 
get your tires balanced.
then
make sure your pinion angle is 0-3* below your driveshaft angle with an sye

you said nothing about pinion angle in your post.
you dont just throw a sye on and vibes go away.
you throw it on. measure driveshaft and pinon angle, and then shim leaves accordingly.
(or cut and turn perches)
vibes at full throttle sound like too much pinion angle since full throttle is when you would most likely get a little axle wrap
you also didnt post how much lift and if you put shackles on or not
longer shackles will point the pinion up a little more.
did you overtighten the pinion u joint straps?
that could mess up the pinion u joint

also how is the front shaft?
how are the control arm bushings?
tres?
etc
 
Whoa Whoa Whoa...ok hold on, first, thanks for the reply and trying to help, but second, I think I posted all that while you were typing as I forgot it in my original post.

I know it HAS to do with something with the SYE and the reason I say this is that I drove it to work, installed it, now everything is the same/worse in certain instances. Tires wont go out of balance just sitting in the air doing the SYE, and Control arm bushing don't go bad thats fast either.

The vibes aren't JUST there at full throttle, I can also hear/feel them just driving down the road from 50-60 where I couldn't before. Plus, when I hit a dip, I feel a thump under my left foot in the floor board area.

I didn't post the angles because I didn't have a tool to measure them at the time!

I know you don't "just throw on an SYE and vibes go away"....but I also know that you don't just throw on an SYE and have vibes get worse with no reasonable explanation. Tires are balanced, I assure you of this, and there is no play anywhere else in any of the bushings or bearings. I did this all at work today on a lift!
 
Maybe this will help understand my problem...I don't know if I'm explaining it good enough lol...this guy is having the EXACT problem I am now having.

http://www.cherokeeforum.com/f2/hack-tap-whipping-me-41211/

By the way, I have 1.25" of spline left on my TC shaft after the cut and I had to cut the yoke down too since I have such a small lift. Others have done the same as I, with more success than I am having. I know it can be fixed, I just need help from you guys figuring out what my problem is.
 
Perhaps the center ball in the double cardan part of your rear shaft is bad. My front shaft on my 87' did that same thing until it blew up and ridded my t-case in half. Then I drove it 500 miles home on half a t-case.... joy... Is your rear shaft new or used?
 
Mr. mud said:
Perhaps the center ball in the double cardan part of your rear shaft is bad. My front shaft on my 87' did that same thing until it blew up and ridded my t-case in half. Then I drove it 500 miles home on half a t-case.... joy... Is your rear shaft new or used?
Click to expand...

Was thinking the same thing on the centering ball. Had some nasty popping/thuds from a bad centering ball on my front shaft.
 
Well it's from the kit in the iron rock offroad kit and it's rebuilt with all new u-joints and I'm assuming that means the centering ball too!

Someone on another post suggested syncing the pinion yoke and the the yoke on the t-case...could this be my problem if they aren't sync'd and how exactly do I sync them??
 
keep0njeepin0n said:
Well it's from the kit in the iron rock offroad kit and it's rebuilt with all new u-joints and I'm assuming that means the centering ball too!

Someone on another post suggested syncing the pinion yoke and the the yoke on the t-case...could this be my problem if they aren't sync'd and how exactly do I sync them??
Click to expand...

do you mean phasing them?

disconnect the driveshaft from the axle pinion yoke, rotate axle pinion yoke 180 degrees by spining the rear tires, reconnect.

edit:
looking back at this, to phase them, you would have to remove the ujoint from the axle and install it by rotating 180 degrees.

i doubt that phasing is your problem. i would take an actual measurement of the driveshaft and the pinion angle to see if the pinion is 1-2 degrees below the driveshaft angle. just looking or eyeballing doesnt work.
 
Last edited:
did find out the source of my thumping under the floor board...the exhast hanger busing on the side of the transmission mount had an elongated hole from the t-case drop...so I fixed that and I also too pics of the angles so I'll post those tonight
 
Ok, here are the best pics I could get today...now keep in mind, the vehicle is in the air, weight off wheels.

photo2.jpg



photo3.jpg



photo.jpg
 
I would get the the shaft balanced, my stock front shaft was bent a tiny butt hair and it was causing all kinds of vibes. Driveline guys took one of the weights off and got it back in line and now there is no vibes. I don't know for sure but I would guess IRO only replaces the joints and checks the double cardon to make sure its OK. Balancing is cheap and would eliminate that issue.
 
Ok so I'll measure it with weight on the wheels and post the results here...the only thing is I don't know what degree shims are in there now since the lift was installed by the previous owner. Any way to tell?
 
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