I have been hearing a whining noise for a while now when I drive my truck. Happens at about 30mph+ and gets louder and more high pitched the faster I go, and occurs when accelerating/decelerating...so I searched the forum and got lots of info on what it could be and what to try. This is how I'm going to tackle it lemme know what you guys think:

I will first start with changing the fluid...it may be low or may have never been changed. Question though: I understand there is an additive to the 75w90 gear oil if I have a LSD? How do I know if I do or not?

Next if that doesnt help I will investigate the rear differential pinion seal as this would be the next cheapest thing after the fluid to check. If it should get to this point I will reply at a later date as I am not totally comfortable doing it with the info I found...perhaps theres a DIY I'm not finding.

 

The pinion seal won't cause a whine. The pinion BEARINGS might. Don't know if it could be classified as a whine though ... more like a scraping sound that varies with load direction (accelerating vs. decelerating vs. coasting). Drive alongside a curb with your window open and speed-up / slow down while listening to see what makes it get louder. If it's not tied to this ... it's something else.

 

look on the rear axle tube, drivers side, for a paper sticker that says something like 3.55 open or 3.55 LSD. if there's nothing there, check for option sticker in glove box or under hood.

if still nothing, buy the additive anyway but don't open it and return it if you don't need it. when you remove the cover, an open diff has no clutches or spring in/around the carrier. also - no broken clips laying in the bottom

if you've got a whine or roar, unless its dry, changing the fluid is not going to help. also, its probably a bearing or gear, and not a seal.

i'd put it up on jack stands and have an assistant put it in gear and let things turn while you listen. be VERY VERY careful i about tore a leg off doing that one time.

if could be wheel bearing, carrier bearing, pinion bearing, or ring/pinion gear noise. could also be drive shaft u-joint

edit - damn, bill beat me to it.

 

thanks fo the responses guys. yes i realize there are several other things it could be and yes i realize the fluid level wont make the whine dissapear but wanted to check all the stupid stuff first and take it fom there and didnt want people to think i hadnt done a search yet:-). i really hope its nothing major, truck has a lot of miles i hate to start investing a lot at this mileage.

 

Yes, but yours was better.

 

if its just gear or bearing noise and you can tolerate the noise, it'll probably run another 200k before it actually fails.