VTX1800N1

I've been trying to locate a bearing noise for some time now. It is absolutely speed related- it does not change with transmission gear or engine speed. It can be heard at all speeds, even right down to 0 MPH. At lower speeds it sounds like a jet engine- the sound you associate with the engine's compressor fan blades cutting into the air. At higher speeds (25-45 MPH) it sounds like poorly worn tire whine. I know it's not the tires because I can hear it slightly with both tires in the air and spinning, and it was just as loud while driving in deep snow where the tires never touched the pavement.

I lifted the rear axle, supported it on jack stands, blocked the front wheels, started the engine and put it in drive so that I could pinpoint the noise with a stethoscope. Unfortunately, I still can't pinpoint it. From under the truck, it just sounds like the noise is coming from the center of the driveshaft. I don't hear any unusual sounds in the transfer case or transmission with the stethoscope. The loudest bearing I can hear is the front pinion bearing in the rear, but then the casing is thinnest there compared to how close I can get the stethoscope to the rest of the bearings in the rear end. From the cab, it sounds like it is coming from the rear of the truck but sound can travel- especially in places like the underside of the bed. There is no unusual difficulty turning the driveshaft and I cannot detect any play in the pinion.

Any thoughts on other diagnostics I can do? The truck has 98K miles, I bought it with 69K. I cannot get a good sound file to post here. There is too much background noise to be able to pull out the sound that I am hearing. It's definitely getting louder over time, though. There is only a very slight gear oil appearance around the pinion input. About a year ago I replaced the differential fluid, so I know that it's not too low. The cost of replacing all the bearings and seals and a TruTrac is going to be ~$800 for parts and another $600 for labor. It's not something I want to sink money into only to find that it was the transmission making noise...

techrep

iTrader: (1)

Sounds like pinion to me but, you listened to it...

VTX1800N1

That's what I think too, especial since I can get the noise right down to 0 MPH. The driveshaft and pinion are the fastest turning parts in there.

krazykoser

I also think it is most likely the a pinion bearing. I was having similar issues with my truck but i noticed the sound would get louder when it was under a load on acceleration or if i downshifted it manually to slow down. pic below is the inner pinion bearing outer race from my truck at 105xxx miles.



I also just finished rebuilding my transmission because one of the torrington bearings was whining. The sound from the transmission wasn't nearly as loud as the pinion bearing was.

VTX1800N1

I took it to the Ford dealer today and they diagnosed it as differential side carrier bearings. Unfortunately, though they quoted me $600 labor to replace all the bearings and seals and install a TrueTrac, they now do not want to do the work. The service adviser stated that they wouldn't even install a Ford Traction-Loc, as it wasn't original to the truck and I could have warranty problems with Ford if something happened during the standard part warranty period. I found that odd, as this means that any dealer-installed accessory on a vehicle will have the same problem?

Oh well, now I need to find someone to do the work for a reasonable price.