All XB8/XT8 diff parts are manufactured from very high tensile steel and as such all parts are specially hardened to provide extra long lifespan and minimal wear. After the hardening process the diff outdrives and inside of the diff gear and diff case are ground to achieve a smooth action of the diff outdrives in the diff assembly. All of the parts are precisely manufactured within very tight tolerances to minimize diff oil leakage; however, if some of the parts with tight tolerances meet together and the tolerances overlap, in some very rare cases the diff outdrives may not turn as smoothly as desired. In case you experience that the car starts to behave strangely and the handling of the car gets difficult after a few minutes of running and the differential becomes very hot, we suggest that you follow this Tech Tip.
Take ultra-fine sandpaper and cut strips the same width as the diff outdrive shafts.
Roll the strip of sandpaper on the diff outdrive shaft, with the grit of the sandpaper against the shaft. Gently squeeze the sandpaper while turning the outdrive in both directions and moving it slightly in and out of the rolled sandpaper. Use a drop or two of light oil on the sandpaper (if desired) for smoother polishing. After finished polishing, carefully clean the diff outdrive to remove any residue or metal filings. Performing this action will slightly polish the diff outdrive shafts; do it for all of the diff outdrives. Make sure not to overdo it or you may damage the diff outdrives.
Cut a slightly larger piece from the same sheet of ultra-fine sandpaper.
Roll the sandpaper on any narrow shaft, for example a screwdriver, with the grain of the sandpaper facing outside.
Insert the shaft or screwdriver with the rolled sandpaper into the diff case and follow the same procedure, move the shaft in and out and turn inside the diff case. Use a drop or two of light oil on the sandpaper (if desired) for smoother polishing. After finished polishing, carefully clean the parts to remove any residue or metal fi lings. Perform this on all the diff cases.
Perform Step 3 for all of the diff gears.
Source : XRAY