I have this weird whining noise coming from the rear of my xj, its there all the time whether driving slow or fast, accelerating or decelerating, I think it may be my differential, how will I know if its bad or my ring and pinion need to be replaced by looking at it? Thanks.

 

You don't see ring and pinion wear unless it's really really bad. Check the diff fluid for metal shavings. Lift the rear and turn each wheel separately, it might be your bearings aswell.

 

just pop your diff cover and look at the gears, they should look clean cut and not chipped or worn. Take some pics and post if you arent sure. If theres metal shaving you might need to be worried. It could just be the fluid is low or contaminated, your going to be putting in new fluid once you pop the cover anyway. make sure to use a new gasket or make one with RTV!

Check your rear driveshaft also if your positive its coming from the rear. Could also be one of the bearings

 

I've the same noise!!! I may have to check as well

 

You probably have some sand issues.. lol

 

ha ha ....
maybe .... esp. these days ....

 

alright thanks for the help guys, ill take the cover off asap and take some pictures for you guys.

 

my vote would go for bearings, or check the driveshaft u-joint. will wait for pics though

 

Most likely pinion bearing on that D35.

 

well i couldnt get off the bolt to check the fluid level, but i think the noise is coming from my axle now. could it be a u joint? Thanks

 

also how do i check the bearings? thanks

 

check the bearing races. pull out the carrier and you should be able to pull the races out by hand. they will have voids in it.
if you ignore it it will get progressively louder like mine has

 

ok well i got the diff cover off and i think everything looks fine, what do you guys think?

 

In my experience differential problems get louder if you accel and then let off the gas, when you let off the gas and start to decel you will hear a loud, obnoxious drag noise, almost like severe road noise from tires but worse.

With the differential you should be able to make the noise change tone by tapping and letting off the accelerator. Wheel bearing noises to me at least seem to get louder when you turn or swerve, when the weight changes from one side to the other you may hear the noise change tone. Drive shafts/u joints tend to clunk.

Noises are hard to pinpoint, if you can make the noise repeat by doing certain actions it may be easier to isolate the problem.

 

Can you thrust the carrier from side to side by hand? does it feel sloppy? not really scientific but if you have excessive slop then you may have bearing issues.