Hi all, truck in question is a '99 5.9l 4x4 half ton with 3:55s, a 46re trans, and 147xxx miles.

A last week I began to notice a droning noise on deceleration. It kinda sounds like its engine braking (it makes sort of the same noise as the flowmaster muffler I have on it). It starts out with a higher drone, and gets lower as speed decreases (lower frequency). The noise is most noticeable between 60 and 40mph, and goes away under 30mph. It makes the same noise regardless of whether it's in gear or not. It ONLY happens when I'm completely off the gas. I think I can feel a vibration in the floor, but maybe I'm just paranoid.

So what do ya think? The rear diff was a little low on fluid the last time I checked (maybe 1/2 to 3/4" below the hole) but the fluid looked good. Or could it be a bad driveshaft u joint? The rear joint was making a loud squeaking noise in reverse but it has since stopped doing that. Any help is appreciated. Thanks.

 

lol. i think you should check your u-joints. they don't heal themselves. the squeaking was your warning that it was going bad, caused by dry metal on dry metal... first they squeak, then they click and clatter. then they break and fall out... block the wheels, put it in neutral, e-brake off, no tension on anything -- wiggle the joint. should be no play.

a bad pinion bearing can roar on acceleration, and then growl on deceleration. with truck jacked up you might be able to rotate the yoke and feel it if its loose and noisy.

 

Also check the output shaft of the transfer case for excessive play......

 

Had the pinion bearing go out sounds alot like tire noise in a way, the way we checked to see if it was tire noise or where the sound was coming from was jack the rear end off the ground then put it in drive, it should make much noise, but if its the pinion it will sound like tire noise with out the tires even on the ground.

 

I'll also go with the ujoint(s), fix what you know is bad first, then move on from there with other diagnostics.

 

its your pinion bearing, my truck is doing the same thing. mechanics at the service station i used to work at confirmed it. just dont have the moneyto fix it yet...

 

pull the diff cover....if you have an LSD, theres a good chance it gernaded inside the pumpkin....

i worked on a 03 Dakota, and it was doing what you explain, plus some binding when turning...i pulled the diff cover and found many chuncks of metal floating around in there.

I'd pull your diff cover and check the magnet/ and for chunks of metal.....

 

Dudes! He already knows at least one ujoint is bad. That will cause the same symptoms.

 

Bad pinion bearings
http://www.youtube.com/watch?v=c23sUvapvzY
http://www.youtube.com/watch?v=wq2GAGBzU4s

What happens when the rear u joint snaps then the drive shaft hits the ground doing 70mph.


What happens when that same drive shaft is promptly run over by an 18 wheeler.


The carnage was a boned drive shaft, snapped yoke and a cracked transfer case.

 

dang, thats definatly noticable....**Sound noted**


and ouch....that d-shaft is done