A lubricant injector used for dispensing a preselected amount of grease when the grease is delivered to the injector in a pressurized condition, the lubricant injector includes: a) a generally cylindrical body which includes an upper grease reservoir adapted to selectively receive grease from a lower grease reservoir, wherein both reservoirs are filled with grease, the body includes a lower grease inlet and an upper grease outlet; b) a shuttling spool slid-ably housed axially within the body, the shuttling spool being adapted to move axially upwardly upon application of pressurized grease at the inlet, and axially downwardly when the grease is not pressurized at the inlet, such that upon application of pressurized grease at the inlet the shuttling spool is urged axially upwardly toward the outlet and configured to close off grease communication between the upper and lower grease reservoirs (114, 142) and substantially simultaneously open the inlet for communication of a preselected amount of grease into the lower grease reservoir; c) a cylindrical plunger received slidably surrounding a portion of the axial length of an outer diameter of the shuttling spool, separating the upper grease reservoir from the lower grease reservoir, where the application of pressurized grease raises the plunger a preselected amount such that a cavity below the plunger creates the lower grease reservoir receiving the preselected amount of grease; d) a cylindrical spacer positioned axially between the top of the plunger and a spacer stop, the spacer adapted to limit the upward travel of the plunger and limit the amount of the preselected amount of grease, wherein decreasing the length of the spacer thereby increases the gap and increases the preselected amount of grease. a) a generally cylindrical body which includes an upper grease reservoir adapted to selectively receive grease from a lower grease reservoir, wherein both reservoirs are filled with grease, the body includes a lower grease inlet and an upper grease outlet; b) a shuttling spool slid-ably housed axially within the body, the shuttling spool being adapted to move axially upwardly upon application of pressurized grease at the inlet, and axially downwardly when the grease is not pressurized at the inlet, such that upon application of pressurized grease at the inlet the shuttling spool is urged axially upwardly toward the outlet and configured to close off grease communication between the upper and lower grease reservoirs (114, 142) and substantially simultaneously open the inlet for communication of a preselected amount of grease into the lower grease reservoir; c) a cylindrical plunger received slidably surrounding a portion of the axial length of an outer diameter of the shuttling spool, separating the upper grease reservoir from the lower grease reservoir, where the application of pressurized grease raises the plunger a preselected amount such that a cavity below the plunger creates the lower grease reservoir receiving the preselected amount of grease; d) a cylindrical spacer positioned axially between the top of the plunger and a spacer stop, the spacer adapted to limit the upward travel of the plunger and limit the amount of the preselected amount of grease, wherein decreasing the length of the spacer thereby increases the gap and increases the preselected amount of grease.