I noticed that, when my ’96 Caprice is backing up on smooth concrete, it kind of grinds and jumped just barely. Is it my gears in rear end? Any other issues could cause this?
It could be any part of the driveline. A dry U joint may be binding. Have you noticed a squeek at very low speeds or when shifting from forward to reverse? Most differentials are pretty robust. If the differential came with posi-traction a fluid change may ease some of the symptoms. I believe these differentials didnot come with a drain you have to remove the cover to drain it. This will allow you to do a visual inspection. Rebuilding a differential requires some expensive measurement tools and a bit of patience. If the gearset is worn out, a junkyard unit makes the most sense from the cost and time perspective.