When Caterpillar first introduced the High Drive (elevated sprocket) system on their bulldozers, one of the advantages was getting the final drive up and away from the ground contaminates like dirt, water and mud. The high drive design also disturbed the drive force over more of the drive sprocket teeth and allowed the sprocket segments to be individually replaced without having to break the chain. Although the new design had some pretty good advantages, there are some disadvantages that need to also be considered.
One of these disadvantages is that on the high drive system, the track chain tends to move or "walk" around more on the sprocket, causing reduced life for both the sprocket and the chain. Caterpillar claims that their SALT (Sealed and Lubricated Track) system helped to reduce this wear and increase the life of the track system.
Another high drive disadvantage, and one that was not correct by the SALT design, is one that is fundamental to the overall design. Having the drive sprocket elevated puts all the drive force on one single chain link between the drive sprocket and the idler, causing the chain to stretch and increased wear on the track pins and bushings. Dozers with the final drive in place of the rear idler distribute the drive force equally across all the track shoes that are in contact with the ground. This is because the very first chain link in contact with first sprocket tooth is already in contact with the ground, so the force is evenly distributed across all the other links on the bottom between the drive sprocket and the front idler.
There are several aftermarket undercarriage manufacturers that claim to have solved the chain wear issues of the high drive system, but unfortunately that means you still must wait for the OEM undercarriage to possible prematurely wear out.
With lots of positive and negative opinions out there about Caterpillar’s high drive design we would love to hear yours.