If I recall correctly, the sway bar is kinked down in the middle to avoid going behind the rear axle cover. I believe what you are talking about is the panhard bar that mounts to the chassis on the driver side, and the axle assembly on the passenger side which is lower than the other end. The panhard bar locates the rear axle assembly side to side, so never drive without one! With the warning out of the way, here goes:

Jack up the rear of the car with it supported on jack stands at the rear jacking points on both sides under the rear doors. Once the rear wheels are off the ground, unbolt the nuts that hold the panhard bar to it's mounting studs at both ends and pull it off. Now you have full access to the rear diff cover.

Once done with the rear diff, reinstall the panhard bar keeping in mind that you might have to nudge the axle assembly to one side of the car or the other to get the mounts to line up again.

This would also be a great time to inspect the rubber bushings on the trailing arm bushings, upper torque rods, and panhard bar, replace as needed.

jorrell
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92 245 307K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!