Really Confused About these vibes..

Alright guys, heres the fast rundown.

97 XJ, 231 with HD SYE, AW4, RE 4.5" lift kit with 4.5" packs instead of the 3.5" packs and shackles, 4.56 Gears on the D30 and Chry 8.25 29 Spline, with 35" KM2s.

I installed this all WITH an SYE, and put my front shaft in the rear. I got BAD vibes on acceleration and the pinion was pretty much in line with the drive shaft. So today I got 2 degree shims and shimmed the rear pinion down 2 degrees, now I dont have as MANY vibes but they are still kinda there.

So I take it for the first highway ride, and over 60 I have a PULSING Vibration that is pretty strong, and it does it holding speed, and also when im decelerating until about 50 then on decel it doesent really vibrate.

Tomorrow morning im going to throw a different shaft in the rear, and completely remove the front, and see what happens.

Do you think I need to shim the rear down more? I have no f'ing clue whats going on, all I know is im getting REALLY mad and about to just give up on this entire thing.

You checked all the u-joint? Made sure all your connections are tight (straps, tail shaft, drive line to the upper yoke, controll arms, etc..)? Make sure your CV on the drive line is tight? Made sure the tires are ballanced right? Make sure your allignment is correct?

Yup.

Im not 100% on the rear driveshaft. Well it was the stock front shaft, and I just put it in the rear, BUT it was perfectly fine in the jeep until now being in the front.

I'm so fed up with this crap, I waited all weekend to get these god damn shims and now its still a 5000lb dildo.

No ones got any ideas?

Please guys, anything. This is my DD and im going nuts.

Sounds like your angles are fine, so my guess is it's something with the driveshaft itself, either with the u-joints or some slop in the yoke.

Double check your axle u-bolts too, just in case, along with the bolts connecting the driveshaft to the SYE yoke and to the pinion yoke.

I'd suggest blocking the wheels, pulling the rear shaft, run it in gear and watch the H&T adapter flange. If it's not installed just right you're gonna get vibes. Been there, done that.

Since you now have a fixed yoke, you can pull each shaft individually, run on just the front shaft, then run on just the rear shaft, to isolate the problem, then go from there.

Its not a H&T though, its a real SYE from Porc.

I put the shaft that was in the front, into the back, and left the front out.

Vibes got a little better, they arent so pronounced but they are still there on acceleration.

On highway over 60 they are there regardless of accel or decel..

Any ideas?

Put it back in the front and try it with no rear shaft and see what it does. It won't be definitive, but it can help get you some info.

The symptoms sound like the pinion is just slightly high, vibes as the pinion raises slighty on acceleration, and could be atr highway speed if there is enough load to keep the pinion raised slightly. Do the vibes go away at speed if you let off the gas, or do they continue?

Keep at it, it's a process of elimination. At some point, you're going to have to determine if the driveshafts and joints are OK.

The vibes on the highway wont go away even when I let off the gas.

Here is how the pinion is sitting now after the shims to bring it down 2 degrees.

That actually looks pretty low...? Tough to tell.

I'd see if you could get the driveshaft balanced and inspected somewhere. Thats my next guess.

Just from the pic, it looks like the rear pinion angle is wrong. If you are running a CV rear shaft, you would want your pinion angle to be close to 1 deg neg. reverse your shims and see if it improves. It looks like you have 4 deg neg to me????

I was told if I have vibes on acceleration, then I need to shim it down.

With NO shims, my truck was HORRIBLY shaking the dash and everything else, since the pinion was in line with the drive shaft. So when I was driving it, it torqued up the pinion more.

Do'h! saw HD but was thinking H&T.

Pinion angle looks low.

TheArsonist21 said:

I was told if I have vibes on acceleration, then I need to shim it down.

Click to expand...

not entirely true, but not entirely wrong.

under acceleration there is ever so slight axle wrap that will bring the pinion up, and if it goes up too far you get vibes, so if you get vibes only under acceleration, that could possibly be cause to shim the pinion down. but as a rule of thumb you want the pinion 1-2* below the driveshaft... buy a 15 dollar angle finder and save yourself the trouble of guessing. from the looks of it your pinion is no where near 1-2* from the driveshaft, i'm going to guess 8-10* as it sits in that picture. the reason for making the pinion a hair below the driveshaft is the same reason i described above, there will be a tiny bit of axle wrap and the pinion and driveshaft will align (for the most part).... hope that helped.

btw, sweet tires.

asp387 said:

not entirely true, but not entirely wrong.

under acceleration there is ever so slight axle wrap that will bring the pinion up, and if it goes up too far you get vibes, so if you get vibes only under acceleration, that could possibly be cause to shim the pinion down. but as a rule of thumb you want the pinion 1-2* below the drive shaft... buy a 15 dollar angle finder and save yourself the trouble of guessing. from the looks of it your pinion is no where near 1-2* from the drive shaft, i'm going to guess 8-10* as it sits in that picture. the reason for making the pinion a hair below the drive shaft is the same reason i described above, there will be a tiny bit of axle wrap and the pinion and drive shaft will align (for the most part).... hope that helped.

btw, sweet tires.

Click to expand...

Basically good info.
It blows me away that people will install a lift, and believe they can "eyeball" the u-joint and drive shaft angles.
U-joint and shaft angles are critical to smooth drive line operation. An angle finder is a must to set up a drive shaft.

The stiffer the rear spring packs, the less upward rotation the pinion will incur during acceleration and at any given highway speed. This would mean the static angle of the rear u-joint (this whole response, by the way, is applicable to using a double Cardin drive shaft) will be lower with soft springs, and closer to "1" degree with stiff springs.
Finding what is correct for your build is entirely individual. This means trial and error. As an example,
I recently installed a rear traction bar. Now my pinion does not rotate at all. Prior to that install, I used 2* shims to lower the pinion angle, which took care of the majority of my vibration. My resulting rear u-joint angle was 1.5* down. I'm running close to 7" of lift, which results in a large u-joint angle at my transfer case; I'm closing in on the max operating angle for the front, double Cardin u-joint, so I'm experiencing some vibrations that no amount of pinion angle adjustments will correct.
The traction bar changed the whole ball game! My vibes came back!
Why? Because my pinion no longer rotates up under acceleration, or at constant highway speeds.
To resolve the vibes to an acceptable level, I had to make custom shims, resulting an a pinion angle of < than 1*; Tom Woods (big daddy shaft guru) says you should run with at least 1/2* rear u-joint angle to insure proper lubrication to the joint bearings).
The morale to the story, is every application is slightly different, requiring shims and other solutions to end up with u-joint operating angles that result in no (or little) vibration. No one can correctly guess at the amount of shims you need.
Why am I going on about this? Well, there're probably 100 threads on this subject here and else where giving the same advice that you're seeing here.
Otherwords, you could have already read "what to do" by now.

Didnt read that last book of a post, but I'll agree with the pinion angle looking to low. The ONLY way to really know is go and get an angle finder and measure your diff angle and your driveshaft angle. Don't worry so much about shimming up or down depending on when your vibrations occur. I went through hell trying to find my vibe problems, youll get there just gotta not overlook the simple stuff.

The next step as been said is I would take the shaft (both for front and rear) and have a shop at LEAST balance them, if not rebuild and definately replace the centering ball in the double cardan.

I kept chasing a rear vibration for months, changing shims, ujoints, until I finally did what I should have done on day one.

BTW - A vibe caused by a ujoint will always be more noticeable when power is being applied to the driveline, and less pronounced when coasting.

First determine if the vibes are in the front or rear.
As Goatman said, dirve around at all speeds on just the rear driveshaft, then do the same in 4hi with just the frontdriveshaft installed.

Usually the vibes are in the rear. I found my cause when I finally jacked up the rear and put the axle on jack stands and then watched the driveline while everything was turning. I could see the rear output flange on the transfercase wobbling as it turned. Turned out the speedometer tone-ring behind the flange on the output shaft was crooked (Rubicon Tcase). This is probably not your problem, but by watching the driveline turn you have a good chance of seeing something wobbling, or turning in an eliptical rotation. You might need to have someone sit inside and increase the speed while you watch. Just be carefull and don't run yourself over.

That diagram is wrong.

Thats how you want it when your DRIVING.

Not when its just sitting there.