Have you loosened the pinion nut? What type of third member are you using?The part number will be in the left side near the bottom the last three digits will be 741,742,489.The 489 case uses a crush sleeve and if you mess with the pinion nut you should have the preload reset or the gears will normally develope a whine driving down the road.As for needing it reset changing a driveshaft I have never heard of that one and I think someone is trying to take advantage of you.