2004.5 Dually Rear End/ Driveshaft Noise?

[DBCooper]

Have a noise coming from behind the cab of my truck. Noise is a "wha-wha-wha" that speeds up with vehicle speed up to about 45 mph where road/engine noise drowns it out. Seems to go away with the exhaust brake against the gears and when I have the coals to it. It's most noticeable with slight power on.
I removed the drive line and all U-joints felt good. The slip joint has some slight play in it. The carrier bearing felt OK with no obvious grinding. Carrier bearing is slightly warm when I pull into the driveway.
I've been running AMSOil in the rear end, changed regularly (30k). Have run a Mag-Hytec since new. Removed the cover and all looks good on the gear teeth. The magnet on the dip stick has picked up some schmaltz, minor metal flake. Gear oil was nice golden color. Refilled the axle with AMSOil, no change in sound.
The noise is pretty minor but I'd like to get in front of it if it is indeed the rear end. Truck has 125,000 miles.
So, the main question is how do I tell it it's the drive shaft carrier bearing or rear end?
Open to suggestions.
Thanks

 

[B.G. Smith]

First thought is dry U-joint. Is the noise frequency at driveshaft rpm or wheel rpm? bg

 

[mfurrh55]

Sounds like ujoint, I thought mine was a bad carrier bearing , took it off and was good, I got to moving driveshaft joints around by hand while it was out and felt a little drag, took it apart and rusty bearings fell out, anyway after thinking ujoints were good I wound up replacing 3 of them and they were bad

 

[DBCooper]

Thanks for the replies, gents. I'd be more inclined to think u-joint myself if I hadn't removed the shaft and moved them around. They feel fine. Suppose they could be just going dry now and still move freely.
Thinking of one piece shaft but want to eliminate the possibility of the noise being from the rear end.
The noise seems to be shaft speed related rather than wheel speed. Kinda hard to tell as it's quiet when going slow, comes on around 15 or so mph.

 

[Prairie Dog]

I just replaced a ujoint that sang like a violin and had no looseness at all. It even felt pretty good but had just a little tiny bit of resistance to flip back and forth.
This is the 5th joint I've replaced on the truck and they never felt loose. They all made noise before they got that bad.

My feelings are that on a truck like mine with no lift, the driveline angles are too straight. The joints simply don't turn enough to spread out the wear.

Scott

 

[p-Bar]

The early years of the 3rd gens had some lubrication problems from the manufacturer . The rep at the SEMA show admitted to me .

 

[Ozymandias]

I just replaced a ujoint that sang like a violin and had no looseness at all. It even felt pretty good but had just a little tiny bit of resistance to flip back and forth.
This is the 5th joint I've replaced on the truck and they never felt loose. They all made noise before they got that bad.

My feelings are that on a truck like mine with no lift, the driveline angles are too straight. The joints simply don't turn enough to spread out the wear.

Scott

0.5° of straight angle is enough, even stock that is more then this.
3.0° is max for a high speed driveshaft.

 

[Prairie Dog]

0.5° of straight angle is enough, even stock that is more then this.
3.0° is max for a high speed driveshaft.

Thanks!
According to my Iphone... I have 1 degree at the diff. (It doesn't do increments of anything less than a degree.) Couldn't find anything to take a reading from on the XFER case but assume it's the same?
It's even less than that with our trailer attached. I'll have to measure it loaded when we take a trip next weekend.

Scott

 

[Ozymandias]

You can measure either Diff or Transfercase, from factory its exactly the same angle on both ends of the driveshaft.

Angles this small needs good equipment to be measured exactly.
I had a digital meter for this at home, fought endless battles with the driveshafts in my old lifted grand cherokee.

The closer you are at 0.5° the less harmonics come from the driveshaft.

 

[ranger 393]

I spaced my carrier bearing down 1 inch right after I bought my truck new due to 70 mph vibe. This fixed my problem. I used to install drive shafts on class 8 trucks years ago, and I feel like the center carrier bearing is to far away from the center joint. (kind of like putting a swivel on an extension and trying keep it from vibrating, you have to control the swivel at the joint) I Had a brake Caliper sticking on the left rear that was making a liitle noise due to the pads rubbing, might be worth looking at...Just my .02

 

[KATOOM]

If the sound/vibration feel is harmonic then its driveline. Generally u-joint noises will increase/decrease with changes in throttle. If its a wheel bearing then it will change while turning either direction. If its transmission then it will change with gear selection. If its engine harmonics then you can test by simply ramping the RPM's while sitting still.

 

[DBCooper]

Thanks for the input, all. Been super busy so haven't had a chance to chase this down. I spaced the carrier bearing down years ago and haven't had any noise or vibration in the past. Rear wheel bearings look perfect and have new rear brakes and new rear parking brakes.
I called the driveline shop in Texas that does the one piece drive shafts and was told that they were months out due to raw material shortages. As soon as I get a few minutes I'll pull the drive shaft back out and have it rebuilt locally. While the truck sits in the garage 99% of the time I do need to get this figured out. Since the splines are a bit loose I don't think I'm wasting anything by starting there.