I have a Chevrolet 1/2 2004 V8, it has only freeway mileage, never off road.Question:  I think the bearings are going out in my rear end, how do I know?Answer:   There are two different sets of bearing in the rear differential: pinion bearing(s) or carrier bearings.Pinion Bearing --- You should observe difficulties with the seal leaking and also you probably will be able to find excessive up and down movements in the driveshaft exactly where it enters the differential, the noise is variable with the speed, but might go away on deceleration, until very low speed where it will come back. When the sound is constant when driving and does not disappear when you let off on the throttle, then the pinion bearings are bad.Carrier Bearings --- You may hear a bearing whine or thump-thump noise, low-pitched growl starting around 20 mph, failure caused by wear or when water and debris entering the differential housing degrading the fluid protection and causing corrosion.Damaged carrier bearings have been reported to cause a vibration and may not make any noise once they go bad. Carrier bearings can be missing big pieces, when ignored the races can spin in housing/case. This problem can be reduced by decreasing fluid change intervals. When changing the carrier bearings keep track of which shims came from which side and make certain that they go back in the same place.Change the pinion bearing simultaneously. If you spun a carrier bearing race in the housing you probably require a new housing, simply replacing bearings will not repair the problem. The spinning race can hone the carrier bearing race seat on housing making the race seat out of round. Thus the space the carrier bearing resides in is now not round and out of tolerance. Making the differential even more vulnerable to spinning a carrier bearing again.When replacing a bearing inside the differential you need to change all bearings, gaskets and seals, contaminants from your old damage bearing propagates completely throughout all bearings in the rear end and it’s difficult to get to clean out even with solvent and air blowing will not be sufficient.Recommend whenever you drain out the fluid from the differential you run it through a paper paint filter, you will notice aluminum colored fluid and may also find large pieces giving you an early idea as to potential problem.You might also want to consider installation of a larger rear end cover this will increase the amount of fluid you can run which will help lower the lube temperature we recommend synthetic differential fluid with friction additive.  You can see the rear end parts we offer on our site.