Tail shaft vibes (i think)

[ktwalker01]

99 4.0L 4x4 4dr np231 AX15 8.25 w/ 3.07 FACTORY SUSPENSION, 207,000

Okay so in the past few weeks ive noticed a weird vibe in the driveline (only under power) between the speeds 20-30 mph. It will do it in what ever gear i stick it in but if i put down the clutch it goes away instantly. So I crawled under the rig I had no play in the yoke on the axle. U joints seem fine.

Now where I did find some play was in the tail shaft where the slip yoke is it has a bit of up and down movement. My question for you all is to my understanding there is a brass bushing in the housing that helps keep the yoke in place. If this thing is worn out would it cause all the extra horizontal play? Or would it be the bearing on the shaft that is no good.

The tranny mount looks good and I recently purchased new rear springs (oem hd) new kyb shocks all around, and new cooper atr tires. When I am on the highway there are no vibes its really just between 20-30 mph with power.

 

[WB9YZU]

The Slip Yoke is external on the 99 and it has nothing to "Center" it, just the splines. There is usually some play there, so I would discount it.

U-Joints usually don't have play until the bearings go away.

Remove the rear DS, and make sure the u-joints move smoothly. Take that opportunity to lubricate the slip yoke. Check the Axle pinion for play. Having a "vibration" at a particular speed and only under power tells me it's either a U-joint which is dry, or a bad pinion bearing.

 

[ktwalker01]

ugh. well the U joints are original with 206xxx on them I'll take a better look at them and see. My front ones have been clicking for the past 56k miles...