Differential gear oil change

This video will show you how to service the differential

https://youtu.be/6F26Kir0OCg

Typically it does not have a specified mileage interval, and as with power steering fluid, you leave it alone until service is required. There are some GM vehicles that have an odd differential design that is prone to developing problems, and changing the gear lube reduces the number of failures. Those are spelled out in the owner's manual, and I suspect it will be listed on the cards the dealers send out to pull you in for those maintenance services. GM has a history of selling vehicles with new designs that are still under test and evaluation, but they let the unsuspecting owners do the testing. As with their rear-steer truck disaster, I think this new differential design will go away too. If you think you might have this on your truck, visit the dealer's parts department and they can search your vehicle's build data from GM and tell you which axle you have. If you have the more trouble-free design that has been around forever, regular gear lube changes are not needed, but if you have a locking differential with internal clutch plates, when you do have to replace the lube, you'll need to add a small bottle of whale oil additive to prevent chattering when you go around slow-speed corners.

Hard to say, but 30 days is just enough to know if there is a problem now, if you get it, check the oil for metal, change any oil in it and listen for any noise at speed, faulty diff's will alter pitch with throttle settings, back off the throttle and the noise will alter, ther is no way of knowing what life you will get.

Mark (mhpautos)

Any magnet is fine. It's job is to collect the tiny particles that break off, mainly from limited-slip clutch plates. You don't want that collecting in the bearings. You'll find the metal appears as a growth of fuzzy grease on the magnet.

If you have anti-lock brakes with a speed sensor on top of the differential housing, those will collect metal filings too, and when bad enough, that will prevent it from generating a speed signal. You don't have to replace the sensor for that. Removing and cleaning it is all that's needed.