Going to change the differential oil in my '98 Dakota, 2wd, 3.9L auto. Best to try to suction it out or take the cover off? If take the cover off, is there enough clearance to pry it loosed over a standard oil collection pan (one of those plastics with a hard top) or does it need to be lifted? Best tool to break the Differential cover loose without doing damage?
It's best to take the cover off. That way you can get a look inside, and check things out. You'll need some RTV to re-seal it.
Sure - though it might be better to use a catch pan with an open top - the gear oil's going to dump out pretty much all at once, and the drain pans that just have the center drain hole might not drain quickly enough to prevent the gear oil from overflowing. Depending on clearance, you may also want to drop the spare tire.
A gasket scraper... there'll be at least one spot where the flat part of the carrier extends beyond the lip of the cover, where you can slide the gasket scraper between the two. A trick is to leave the top two bolts of the cover in place, just loose (very loose) - that'll prevent the cover from falling when you break the RTV seal.
Once drained, clean the cover and carrier mating surface with some brake cleaner, and run a nice 1/8" bead of RTV around the perimeter of the cover, going to the inside of the bolt holes. Slap the cover back in place (try to get it aligned the first time - don't want to be squishing the RTV back and forth too much), and torque the bolts to 25 ft.lbs. in a criss-cross pattern. Let it set up a bit, then re-fill with gear oil, and friction modifier if you have a limited slip.
On some rear axles you can remove a bottom bolt on the cover to drain it. Never owned a Dakota so I can't say about them. I like to remove the cover just so I can look for signs of problems. Like metal in the bottom:(
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