A slack adjuster that is protected against environmental contaminants via a series of holes positioned circumferentially around each end and covered by a sleeve having a slot is aligned with one of the series of holes while covering the remaining holes. The sleeve protects against infiltration of contaminants at the ends of the slack adjuster and allows any contaminants that do infiltrate the slack adjuster to be expelled through the aligned hole and slot. The central portion of the slack adjuster may also be protected by including a series of circumferential holes that are selectively covered by a sleeve having a drain positioned to align with the lowest holes while covering the remaining holes.