Roaring/road noise under floor

[jdmccright]

Tried the search and coudn't find anything specific so I'll post a new one for this.

'95 C2500 ext. cab w/ 350 and 4l60E, 203k miles. I hear a noise like a bad wheel bearing (roaring/road noise) at low speeds, but it seems to be coming from under the floor/seat area. I've changed all the wheel/axle bearings (probably needed it anyways since it was a gooseneck/5th wheel trailering truck in the past...sports the holes in the bed to prove it), but the noise continues. Now I'm thinking the u-joints and/or center support bearing, but wanted to hear from others.

Also, while changing the rear axle bearings (6-lug, 9-1/2", G80), I noticed that while the truck was in neutral, rotating the axle in one direction (CCW, I think) to remove the differential pinion shaft was very difficult, while the opposite direction (CW) was easy. Plus, when I did rotate it slowly CW, I heard a sqeaking sound inside the tranny at the rear part of the pan....thought that odd. I don't hear any squeaking noise while the truck is moving, but it may be masked by the roaring noise. Is that a dead/dying internal bearing that can be accessed by removing the extension housing? Or is it just a dragging slip band? Or just a 1-way clutch doing its job albeit noisily? Any thoughts would be appreciated.

Right now the primary concern is the noise, the truck drives and shifts fine and there is no clunking noises in the driveline. Thanks for the input.

[777stickman]

From your post the 1st thing I would throw at it are the u-joints. With the mileage on it this would be a good thing to do even if it doesn't fix the issue.

[jdmccright]

Ayup, I'm thinking the same thing, along with that carrier bearing. This truck went through some serious slop in its past. Wouldn't be surprised if dirty water & crap got in and screwed up that bearing. Just took it for a closer drive/listen earlier tonight. The sound doesn't change with the transmission shifts but would change as the rear suspension moved, so I think it is definitely from flexure of the worn joints. Time to throw more money under this truck...will keep posted.

[Chevy-SS]

Originally Posted by 777stickman

From your post the 1st thing I would throw at it are the u-joints. With the mileage on it this would be a good thing to do even if it doesn't fix the issue.

Yeah, I agree. The u-joints could be noisy, even if they aren't real loose.


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[jdmccright]

UPDATE....

Got under the truck and tried to remove the two-piece driveshaft. I had to remove the whole thing together because the two halves would not separate. The slip yoke slides fine, but it will only slide out so far and then stop. Manuals don't go into detail on how to separate the two halves to replace the carrier bearing (yes it's the ctr bearing...very loose) so I assumed it just slipped in and out like the tranny yoke. Wrong! Anybody got an answer?

[jdmccright]

UPDATE...

I am told by the local repair shop that the driveshafts are separable by unscrewing the slip-yoke seal cap (has a zerk grease fitting in it). But mine was so frozen from age and presumably dirt, I had to yield to the pros. So, it is at a driveline specialty shop getting a new center bearing and yoke seal/cap installed. I'm bending over so they can reach my wallet easier when I get screwed. Stay tuned....

[K10]

One of the easiest things to do to find out is jack up the rear end (both wheels off the ground). put the truck in drive, and hit the gas till you get around 60 mph... then, shift to neutral, and cut off the truck... the wheels will keep spinning for quite some time. Listen carefully and see if you hear anything roaring/grinding as you say. try to locate the source of the noise...

[jdmccright]

I would think you'd hear it well below 60, and I honestly wouldn't go UNDER my truck that way unless I was desperate (and had front wheels good and chocked).

I knew it was a bearing, but couldn't place it. I figured the truck was so old that it was the wheels...they're easier to replace and probly needed it anyways.

id rather undo the six bolts holding the driveshaft and spin the ctr bearing free...or in my case, I could just wiggle it it was so gone. gonna reinstall today. Thanks for the tip.
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