Rumbling howling noise (pinion bearing?)

The short: What does it sound like when pinion bearings are going out? Can I check them before pulling the third member?

The long: About two years ago I bought a '99 V6 4wd Xtracab. During the test drive it about rattled my teeth out, and I asked the seller about it. She said, it's a truck, they all ride this bad. RIGHT. Anyway I qucikly diagnosed a entirely blown U-joint at the rear diff (half of one of the cups had already broken and fallen out). After negotiating a good discount on the truck due to u-joint, I gingerly drove it home and promptly replaced it.

The truck has never been all that quiet, but over the past two years it has been slowly getting louder. It's mostly a rumbling/howling noise but is now loud enough I have to crank the radio to drown it out. It is undefined as to where it is coming from. It varies with vehicle speed, but not engine speed, gear, or if I am accelerating, coasting, or braking. I don't feel any vibration or shaking. I don't think it is a wheel bearing, I have checked all 4 corners and there doesn't appear to be any play in them. I did replace one of the rear bearings last year due to a leaking axle seal, So my current line of thinking is that the really bad u-joint caused premature wear to start on the pinion bearings.

Any thoughts or suggestions on things to check? Thanks!

 

Did you check the other ujoints? Even when the fronts go bad they make a noise (spinning all time)

 

Typically a bad pinion bearing will change dramatically in pitch when on/off the throttle. At least they always did for me. When they get really loose you can sometimes move the pinion flange by hand too. Wheel bearings don't change with throttle input though. You can't really check for play in the bearings on these by rocking the wheel like on old school cars either. Its a preloaded dual race bearing on the front. They won't move until they are so smoked you can barely stand to drive the truck any more. Rears will sometimes have a very slight amount of play up and down. But you don't feel this by rocking the wheel. You have to try and pick up on it.

 

So this afternoon, on a friends suggestion, I pulled the entire rear driveline and test drove it in just "FWD" mode. Noise was still there, although maybe the pitch or tone of it changed.

I didn't think the front driveline spun that much when in RWD, but I will probably try running just the rear driveline and see if the noise remains.

Hmm, that pitch info is helpful. I guess I'll try all the wheel bearings before I go the route of the pinion. I will probably do the other rear first, since I already have the jig made up to press it and the other side was pretty easy.

Any other tips on diagnosing it down to a front wheel bearing? It looks like a PITA to replace...

Thanks!

 

front driveline should only be turning when in 4wd. the cv axles will turn if you had ADD or if you have the hubs locked depending upon your model. have you greased the entire driveline? including the double cardan center joint?

 

Yup, greased the entirety of both drivelines, including the double cardan joints. And yes it does have the ADD, and I didn't think that it should have spun (other possibly just some drag inside the diff). I realize the CV shafts still spin, but I've never heard CVs rumble, I've always just had them "click" when going bad (on other cars).

 

Front wheel bearings are actually easier to change than the rears if you have a press. Just take the whole spindle off the truck. Press the hub out, remove snap ring, press out the bearing, then reverse the process.

 

grease the fitting between the 2 u joints at the double cardan?

 

any luck ????? i have a guy currently having a problem like this. he says that when ever he turns left or right ot makes a humming noise in the rear axle. where wondering if its the bearings or actual gears that need to be replaced. keep us posted. anyone else has had this problem ??????

 

Unfortunately I haven't had time lately to do some further investigation. The truck isn't a daily driver for me so it has taken a back seat to some other stuff. I will post an update if/when I figure it out though.

 

Noise while turning is usually wheel bearings. Noise which changes under/off load is usually driveline. Drain the rear diff to look for metal shavings. Lots of large chips or flakes are cause for alarm. A small amount of metal dust is ok.
As stated earlier, checking for play in the pinion shaft, with the driveshaft removed, would be a good indication of pinion bearing health.