Rear-end growling noise

[firestarter]

Hello jeep gods,

Hoping that this rings a bell to someone. I have a 2000XJ with a RE 3.5" lift (came out slightly more), did the lift about 6 months ago. Recently I've noticed a "Growling" noise when decelerating at highway speeds and I can continue to make it growl if i don't fully take my foot off the gas. On a scale of 1-0, lets say 1.0 is 75mph and 0.0 is idle..... if i go from 1.0 to .3 and stay there it will continue for a bit of time.

The noise appears to be coming from the rear-end while in 2wd and, to me, it could be anything from an exhaust leak.... maybe backpressure or something, to the pinion ...

The following article pretty much describes the situation, very difficult to diagnose without hearing it but I thought I'd shoot the question out to you folks.

Pinion bearing ?!? Need help diagnosing plz! - JeepForum.com

I just crawled under it and gave the driveshaft a good shake/turn and there is a little play.... just a little.... is this normal? Nothing, visually, appears worn down .... everythings still nice and rusty.

Thoughts?

 

[firestarter]

I should also mention that if i get off the throttle immediately and/or brake as well I don't get any vibrations or noise. When people mention that they have vibrations due to an incorrect angle or a bad pinion is it a heavy vibration or something very small and just annoying?

 

[Knicy6tj]

First check fluids. In both diffs and transfer case. Is the driveline play from a U-joint? Or just a natural play from the pinion about 1/4 inch deflection would be acceptable. If you think everything is still good. Try putting it up with all wheel off the ground. Get someone to run it in drive to your problem area. And listen to the diffs and transfer case with automotive stethoscope. If there alot of noise from your rear end your prolly gonna need a rebuild. And might wanna possibly think about an upgrade back there.

 

[firestarter]

Thanks. I'd say there's 1/4 rotational deflection on the rear driveshaft, good to know that's about normal. What's the process for checking the diff fluid level? Can't say I've had to do such yet.

As for an upgrade are you talking about a SYE setup?

 

[MudderChuck]

Usually there is an oil leak at the pinion seal when or if the pinion bearings start to go.
The lift makes you suspect the U-joints. If you look very closely at the U-joint you will see a rubber seal around the cap. If the rubber is covered in rust dust, it is likely you need a new joint. I jam a bar of some type into the pinon yoke so it hits the body and is solid, then twist the drive shaft. Any movement at the rubber seal between the X and the caps usually means it is time for a replacement.
If the roar changes pitch during a moderate curve while driving at a constant speed, it may be the carrier bearings.
It may be anything, I've been fooled before. Sound travels in the drive train and where it sounds the loudest may be a long way from where the sound is being generated. One trick to get it localized is to drive next to a brick wall and have someone hang out the window and listen. Or like mentioned, put it up on jack stands or a lift and run it in gear. Be careful under there, everytime I mention running it in gear on a lift, I think back to a buddy of mine getting his hair caught in the drive shaft, it was ugly.

 

[lambo]

Not for nothing but I had a loud rotating grind that had me thinking drive train. Got underneath and found that the ex oust shifted and was rubbing the gas tank, A few adjustments and no more grind. Noise under the jeep or any other car for that matter is hard to isolate so dint panic it could be the stupidest thing. I had a noise that sounded like u joints and it turned out that a clip under the inner wheel well had let go and the thing was off by about a 1/8 of an inch. Hard to isolate from in the jeep but it was loud and I could not figure out what it was without actually walking beside the car while my son backed up and i had my head down in the wheel well. So i popped of the clip reattached it and to my amazement no more grind. Its the simple things that sound like death when in the car and believe me when i say what sounds like grinding could be from something that has the littlest rub will and will sound like death. My muffler hitting the gas tank could not be seen because while under the car it looked fine, but put someone in the car and rub-u-dub-dub. So good luck and have fun.