1997 XJ vibration question.

[Badlogin]

I have have been struggling to locate a vibration that starts around 45mph. I need to see if there's anything I missed. It's had the same vibration every since I bought it. It had 2 inch blocks and an old lift with a hack N tap.

1. New Spin Free front hub conversion to remove the front end from the equation
2. Rebuilt the np 242 t-case and a installed a new Tom Woods SYE.
3. New rear leaf springs, (no blocks).
4. New Iron Rock .75" HD rear shackles
5. New Front and rear Adams Driveshafts with. double cardan.
6. Set the driveshaft pinion angle to a couple. degrees below centerline.
7. New StinkyFab transmission mount.
8. New ARB rear locker.
9. New rear carrier bearings and pinion bearings.

So far none of that has helped. The Vibration is pretty consistent from 45 to about 60ish. Then it gets more aggressively worse and stays no matter how much faster you go. The more aggressive higher speed vibration is affected by how much throttle/torque is given like axle wrap. I do not get axle wrap from a standing start. I have a video I will try to add a link. It is before I lowered the pinion angle. So that's why it looks a little high.

 

[Tim_MN]

What does the front pinion angle look like? Are the motor mount fresh? What kinda rims and tires? Have you had the tires balanced with a Hunter Road Force balance machine?

Remove the front driveshaft, and repeat the drive that causes the vibrations. If necessary remove the rear drive shaft, shift to 4x4 Hi, and repeat the test drive.

 

[Badlogin]

Thanks for your reply.
It has front hubs and they are unlocked. Yes it has new motor mounts and trans mount. I have pulled the front driveshaft and it still has the vibration, I can feel the vibration in my seat. Its a harmonic driveshaft vibration not a tire vibration. However I have been contemplating getting the tires rotated due to slight feathering on the fronts. It will give me a chance to put an eye on the steel wheels and watch for hop or runout.The Vibration increases if I'm at speed say around 65mph going up hill like an increased pinion angle due to torque (axle wrap). If I'm at speed and let off the throttle the majority of the Vibration goes away indicating there's something going on with angle. Like I said since that video I have added 2 more degrees down of pinion angle and didn't correct the problem. As far as pulling the rear shaft goes and driving on the front. I'll give that a try. However with the 5.5 inch lift Im sure I'll have plenty of vibration.

 

[Tim_MN]

My 2000 has 5.5" of lift and no vibrations until about 85 mph.

The symptoms described, suggest a bad u-joint, improperly balanced drive shafts, or excessive pinion angle.

 

[Badlogin]

My 2000 has 5.5" of lift and no vibrations until about 85 mph.

The symptoms described, suggest a bad u-joint, improperly balanced drive shafts, or excessive pinion angle.

I agree. However it's the 3rd driveshaft, 4th if you count the first one I rebuilt. And we started with pointing the pinion straight at the output yoke of the SYE on the T-case. And have since tried several degrees increments below pointing pointing at the output of the Tcase. That has improved the vibration. But now the pinion is entirely to low in my opinion.

 

[Tim_MN]

With an SYE, I have always added about 1° of shim for each inch of lift. Are you measuring the t-case angle and axle pinion angle from machined surfaces?

Tom Woods Driveshaft calculates rear axle shim size. Divide the length of the drive shaft by the sum length of the drive shaft plus pinion shaft, I always use 12 inches as an average length for the pinion shaft. This division problem will give you a decimal number. Now multiply that number by the amount of change you need to make in joint angle. For example, your drive shaft is probably around 33", we will use the 12" for the pinion, so 33/45 = .73. Now multiply .73 by the amount of change needed, in this case around 6 degrees. .73x6=4.38. This means you should use a 4 degree shim.

 

[Badlogin]

With an SYE, I have always added about 1° of shim for each inch of lift. Are you measuring the t-case angle and axle pinion angle from machined surfaces?

Tom Woods Driveshaft calculates rear axle shim size. Divide the length of the drive shaft by the sum length of the drive shaft plus pinion shaft, I always use 12 inches as an average length for the pinion shaft. This division problem will give you a decimal number. Now multiply that number by the amount of change you need to make in joint angle. For example, your drive shaft is probably around 33", we will use the 12" for the pinion, so 33/45 = .73. Now multiply .73 by the amount of change needed, in this case around 6 degrees. .73x6=4.38. This means you should use a 4 degree shim.

Very insightful. I've never heard anyone give a detailed explanation like that before, thank you. I say it's a little over my head standing here at work glancing at it. When I get home I'll try study it a bit further.