how to deal with rear diff noise

[friendly_jacek]

I did a search and was surprised to see little relevant post on this in this otherwise very helpful forum.

The story is that my MY 2000 legacy wagon (AT) with 50000 miles has had this low to medium intensity noise coming from rear diff since 40000 miles or so (cant be precise, my wife is the primary driver). It is not a high pitched whine, more like a medium frequency rumble. Starts from 40 mph and is pretty much constant with no change with acceleration or FWD fuse. It is more difficult to hear at hwy speeds (~70 mph) because road/engine noise masks this.

The diff fluid is not low as I checked several times. I put 75W90 synthetic redline fliud in at 42000 with no change in noise. The original fluid did have a lot of very small metal particles near the magnet but I am hearing that it is normal.

My 5 year/60000 drivetrain warranty expires soon. Is this something I can ask the dealer to fix or is this expected with the age of the car?

Is heavier fluid (80W140 or so) going to help with the noise?

Any additional insights into this issue?

 

BTW, the car was mostly trouble free with the usual several recalls and a TPS failure (ouch, $330). It eats thrugh the brakes and tires though (second set of pads and 3rd set of tires installed at 50000 miles), 50/50 city/hwy driving with ~5% towing duty.

 

Thanks a lot!

[99obw]

My experience with my Jeep is that the rather noisy rear diff is quieter on 75w-90 than it was on 75w-140. I have heard that the thinner lube lubricates the bearings better. I think the higher viscosity fluid is intended for diffs used for towing, where the temps will be higher and the operating viscosity will be about the same.

 

The metal particles are definately normal, nothing to worry about.

 

Any chance it could be a rear wheel bearing? Rear bearing problems seem to be relatively common on late model subies.

 

Diff problems seem to be rare on these cars. I have never ridden in one with a loud diff nor heard of someone having that problem. Regardless of cause I would pester the dealer to have them fix it. Reproducing the problem and making them know that it isn't normal nor acceptable will be the key.

[The Dude]

I would absolutely take the car to the dealer and put the problem "on record" during the warranty. This problem is NOT normal. It may very well be defective/prematurely worn hypoid gears in the diff. If so, the noise will likely get worse and worse. Eventually the noise may actually make you abandon the car, I'm not kidding. This is an expensive repair when out of warranty. You are always smart to have the car repaired during the warranty period. Dealers frequently say " let's wait and see what the problem is, and we can talk about repairing it then". Well, once the warranty period is over, things don't always work out that way. Bad hypoid gears frequently make a kind of "roaring" noise.