Think my pinion bearing is going south...

[cam.man67]

Since I got back from Wyoming, I've noticed a soft hum (only when the windows are up and the radio is off) above 40 mph. It changes pitch based on speed, and it's there most only on deceleration. Does that sound like a pinion bearing to you? It doesn't seem like its getting louder, and I've really only noticed it in 3rd gear, though it may be there in 1st and 2nd as well.

If so, any idea what a reasonable cost is for a shop to get it replaced?

 

[Inertia]

Replaced my first response when I realized it could be taken in a very wrong way,, my apologies...

If you can get it up on stands, use a stethescope, or piece of dowel, to listen to the front and rear pinions while in gear and running..

Could it be tire noise?

hope it helps...

 

[TrailBeast]

Since I got back from Wyoming, I've noticed a soft hum (only when the windows are up and the radio is off) above 40 mph. It changes pitch based on speed, and it's there most only on deceleration. Does that sound like a pinion bearing to you? It doesn't seem like its getting louder, and I've really only noticed it in 3rd gear, though it may be there in 1st and 2nd as well.

If so, any idea what a reasonable cost is for a shop to get it replaced?

From the information so far, it sounds like it could be.
(Could be)
Could be a number of other things too, like one of the rear bearings in the trans.
Or a ujoint can do that too.

 

[67Dart273]

X2 above

How "high pitched" is it?

Could be something in the normally isolated metal engine/ trans/ exhaust assembly that is touching the body and transmitting sound

Could be a rear wheel bearing?

Could be pinion, or ring/ pinion GEAR wear, how about LOW FLUID level in the rear?

 

[RustyRatRod]

If it's a high frequency hum, it's probably driveshaft speed and could be a pinion bearing. If it's tire speed, more likely a wheel bearing. Pay attention next time you drive it and see if you can determine that.

 

[cam.man67]

Thanks for the comments, guys

Could be a number of other things too, like one of the rear bearings in the trans.
Or a ujoint can do that too.

Rear bearing in the trans...that's a thought. I haven't been able to exactly diagnose how far forward/backward the sound is coming from...I'm just assuming it's from out back, ut I guess this is possible. How easy is that to replace on an 904?

I've never heard a u-joint doing that? I thought they always just clatter and chirp and bang when going into gear and such? I have bad ujoints in my jeep, that's basically what they do.

X2 above

How "high pitched" is it?

Could be something in the normally isolated metal engine/ trans/ exhaust assembly that is touching the body and transmitting sound

Could be pinion, or ring/ pinion GEAR wear, how about LOW FLUID level in the rear?

About 3 weeks ago, I noticed at idle that the muffler or some piece of exhaust was rattling against the body. Everything appeared to be tight down there and the sound has since gone away.

I just put a new gasket on the rear in February, ever since then the axle housing is dry. I don't think I'm low on fluid, but it's worth a look. The guys that replaced my axle shaft bearing back in february said the ring and pinion and spider gears were all fine, not worn. I don;t think it's that, but thanks for the suggestion.

If it's a high frequency hum, it's probably driveshaft speed and could be a pinion bearing. If it's tire speed, more likely a wheel bearing. Pay attention next time you drive it and see if you can determine that.

Almost positive it's driveshaft speed.

 

[TrailBeast]

904, then it's probably not the trans.
The reason it could be a ujoint is that they dont always fail loose.
Somtimes they will get dry and bind up causing a vibration, or get out of balance from bearings breaking up inside them. (But still not be loose)

So it still could be a ujoint, pinion bearing, carrier bearing, or rear gears.

Might want to get one of those stethoscopes and see if you can track it down that way.
I use a screwdriver and put my ear against it, but the stethoscopes are easier to use.

 

[Supershafts]

If it's just the front bearing you would probably be near $100 area, but if it is the front bearing only which is what it sounds like it is, the other bearing is also right now being abused and taking some added punishment.
I would visit a local shop that has driveline experience and has a good reputation and have them do all the bearings at the diff rather than the only one that at this time needs attention, i would expect the cost depending to be in the $300 area