Many earth-working machines, such as, for example, loaders, tractors, and excavators, include tracked undercarriages to facilitate movement of the machines over ground surfaces.  Such undercarriages include drive sprockets that rotate track assemblies about one or more idlers or other guiding components to propel the machines over the ground surfaces.  Each track assembly includes a pair of parallel chains, each made up of a series of links, joined to each other by pins and/or bushings (the combination of which is sometimes referred to as a cartridge assembly).  Due to wear from abrasion and impacts experienced during use, undercarriage maintenance costs often constitute more than one quarter of the total costs associated with operating the earth-working machines. 
A known cartridge assembly for coupling links is disclosed in U.S. Patent Application Publication No.  2012/0267947 by Johannsen et al. (“ the '947 publication”).  The cartridge assembly includes a pin accommodated within an inner bushing, which is, in turn, accommodated within an outer bushing.  End portions of the inner bushing are surrounded by inserts, and end portions of the pin are surrounded by collars.  The pin is provided with a central, axially oriented lubricant channel, which serves as a reservoir for lubricant and delivers lubricant to a gap between the pin and the inner bushing, and to a gap between the inner bushing and the outer bushing.  The lubricant is retained by seals positioned between the outer bushing and inserts, and by seals positioned between the inserts and collars positioned around the axial ends of the pin. 
The cartridge assembly of the '947 publication may provide certain benefits that are particularly important for some applications.  However, it may have certain drawbacks.  For example, the seals described in the '947 publication as being positioned between inserts and bushings may increase the complexity and cost of the cartridge while reducing the expected wear life of the track joint assembly.  The disclosed embodiments may help solve these problems.