I google searched this and got a lot of hits.
none of them verified what was causing it.
Its not the u-joints I put new ones in.
A lot of the posts said get a sye .
Anyone have the cure?

 

Pinion nut came loose on my pickup and rumbled decelerating

Is it a new problem or always done it

 

I've only had it a couple of months.
probably put less than 40 miles on it.

 

Does it have a suspension lift on it?

 

I can make no assumptions or guesses that is how dealership techs attempt to fix vehicles and why they always fail

 

It has a rubicon express 3.5

 

Is it a vibration, like a shaking or just a noise? Nice looking Jeep. What year?

 

its a mild vibration that you can hear, its only when you let off the gas.
its a 1998,thanks

 

Same here. Could be due to an improper rear driveline angle putting stress on the slip yoke. There are things you can try to eliminate it if they haven't already been done. I see you've already done the u-joints. You can shim the rear at the spring perches. Do a transfer case drop. I've tried all but the t/c drop and still have the problem so am installing a sye w/ cv driveshaft. Below is what you want the angle to be with a std u-joint and with a cv u-joint.


Also see post number #29793 here:
https://www.cherokeeforum.com/f67/al...579/index1987/

 

Jim i have something similar when letting off the gas at highway speeds that showed up after i did my lift. If you tap on the gas a little bit it goes away right?

If so since mine only showed up after the lift in chalking it up entirely to that.

 

"If you tap on the gas a little bit it goes away right? " Yes jbudz thats IT!
So..... sye + cv drive shaft?

 

The next thing I would like to see is a pic of your output shaft/slip yoke and your pinion U joint

 

Pics would be good. Also I forgot to mention that the first thing I did to verify where the problem was coming from was to remove the rear driveshaft and drive it a while (in 4H).

 

 

Thank you Jim, pics are worth a thousand posts. I think I see two things here. One is not quite a problem, your pinion is a little to high, but not by to much I think if you are not getting vibes all the time. The other as near as I can tell is that the yoke is too far out on the tail shaft. I cannot really tell since you have the rubber boot on there, but I think what is happening is that when you decelerate the spring is flexing a little and the pinion is going down just far enough that the yoke goes out just far enough to get a little sloppy. Sometimes you can remove the drive shaft and grease the splines and it will take out a small amount of slop, but I wouldn't count on it. Try it and see if it works. The only total fix is to put in a slip yoke eliminator. It is the best fix and you won't be sorry you did it once you get the pinion angle set properly like the diagram from EZEarl. That diagram is directly off the Tom Woods driveline website