I have a 2000 4 WD Blazer with about 150,000 miles that has developed a drivetrain whine when getting over 15 mph. The whine gets louder the faster I go. It goes away when I take my foot off the accelerator, and then restarts when I put my foot down on the gas. It has a standard differential; so I raised each rear wheel separately, put it into gear and listened for noise to see if it might be one side bearing or the other; I heard the same noise regardless of which wheel was raised. I removed the differential cover to look for shavings and couldn't find any; although the differential fluid was on the low side. The other thing is that it is very difficult to determine if the whine is definitely coming from the rear of the car. If I was completely sure that the differential was the problem I would proceed on replacing it; I sure hate to do this though if it might be coming from another drive train component; e.g. the transmission. Does anyone have any suggestions on how to better determine if the noise is in the differential or the transmission? And if it stems from wear in the differential; as opposed to overt damage such as teeth breaking off; is this something that I can just "live with" for awhile?

 

I would suggest having a freind drive yer truck and you start in the back with your ear to the floor and work your way forward to see if you can hear an area where it might be coming from. Another way to see if its in the tranny is to put the transfer case in N and put the transmission in gear and raise the rpms slightly to see if you hear it then (of course put the parking brake on and do it in a clear area in case, for some strange reason, it decides to jump into gear). Another thought is put the rear end up on jackstands and see how much "play" there is in your pinion gear.....rotate the driveshaft with your hand to the left and right quickly and see how far the pinion yoke moves in and out, if it seems like a lot then it might be time to replace the gears. You could also rotate the driveshaft in one direction and see if the pinion bearing is making noise. Just a couple thoughts.....

 

I checked out the pinion gear today; and it had minimal play; i.e. virtually none. Ditto the universal joint. I'm not sure how to go about your first suggestion though; putting the transfer case in N and put the transmission in gear. Could you give me some more input on that?

 

If you have a push button engagement then you would have to find the procedure to put in N, should be in the owners manual...maybe under "How to tow vehicle" but not sure. If its a shift into 4wd with the stick then just put it into N, just be sure to turn off the motor before shifting the transmission into a different gear after drive, there will be minimal drag on the trans to slow it down and you don't want to shift it while the trans is still moving, could cause major issues and turning the motor off is the easiest way then just give it a minute or so to stop.