Update: Now available for one-piece Land Cruiser Transfer Cases!
This shift spring is an optional upgrade part for your transfer case that provides a stronger engagement and a better overall shift feel. Additionally, by applying more pressure on the shift detent, this spring decreases the chance for an accidental or unintended gear shift.
If your transfer case is popping out of gear on the trail, then this heavy duty spring may help!
On Hilux Pickup/4Runner applications, they are easy to install from the outside without disassembly requiring only a 6mm hex socket and possibly also a small magnet to extract the stock spring. Land Cruiser applications require more work to replace as the low-neutral-high spring is located inside the case.
In general, only (1) spring is required per transfer case, which is always installed for the low-neutral-high shift rail (this is the driver's side spring on Hilux Pickup/4Runner applications). However, it is common to get (2) and replace both springs so that the shifting performance of both patterns is improved as a whole. In other words, "if you are gonna replace one, you might as well replace both!" If you have a dual case Crawl Box, then be sure to pick up an extra spring as Crawl Boxes also use (1) spring.
Be sure to add a thread sealant during reassembly such as Loctite's Hi-Tack Gasket Sealant.