This shift drum replaces the O.E.M. KLX / DRZ shift drum and allows use of the 4th gear that is blocked out on the stock bike. It can also be used to change the "L" model 4-speed motors to "all-up" shifting. O.E.M. quality part. Installs the same as stock 3-speed shift drum. Requires complete engine disassembly to install. Note: On the "L" model bikes, you will want to eliminate the neutral-safety-starter switch (by grounding the wire on the harness).