Drive shaft vibes (front vs. rear)

Getting ready to do the SYE thing on my 2000 xj. Bad vibes after installing RE 3.5" lift. I noticed in most of the forums concerning driveline vibes that most of the concern is with the rear shaft vibrating. Why are the vibes more likely coming from the rear and not so much from the front? If the lift is changing the pinion/drive shaft angles on the rear, wouldn't it also be changing the front angles as well? Should I also be concerned with the front shaft? The RE kit once installed was closer to 5" of lift.

The big worry when lifting late model XJ's is the slip yoke on the rear output of the transfer case. The front output doesn't have a slip yoke. The front drive shaft simply extends in length but the rear drive shaft is a fixed length - so the slip yoke extends. As the slip yoke extends it starts to wobble and cause a vibration.

Yes, castor-vs-pinion angle can be a problem in the front. However, the lift manufacturer should have taken that into account already. I got adjustable control arms to give me more options. I strongly recommend getting adjustable upper control arms.

-Brian

Also, the front shaft already has a cv joint at the t-case.

The other problem is the operating angle of the u-joints. Google 'u-joint angles', there are plenty of pages about max operating angles of u-joints and the relationship between driveshaft; pinion; and operating angles to driveshaft length and rpm.

sgtmack said:

Also, the front shaft already has a cv joint at the t-case.

Click to expand...

CV joint is not a cure-all if the pinion angle is incorrect. Buy an angle finder and check!

Both driveshafts on mine vibrated after lifting. The back was cured in the usual way, SYE with a slip jointed driveshaft. The front was not so easy. The pinion angle caused the vibration. When I rotated the pinion up far enough to stop the vibes the caster angle was thrown way off and the Jeep drove badly. I ended up installing the Mile Marker hub conversion so I can keep the front axle from rotating while on the road.

Dont forget he's got a 2000 w/ a LP D30 so the angles are going to be even worse!