S&S primary mainshaft bearing race has a modified design, which positively prevents the race from walking into the mainshaft seal and potentially destroying the output gear. This race is not included with the S&S transmission, but may be purchased separately. This improved bearing race can be retrofitted to provide the same protection for stock transmissions as well. Fits All 1991-2005 Harley-Davidson big twin and 2006 Softail and FLT Models S&S Part #: 56-5089