To keep the gear pump housing located within the rear section of the transfer case, five indexing tabs are employed.
Over time, the indexing tabs on the pump housing begin to rub and eventually wear a hole through the transfer case, allowing fluid to leak out.
This means no puddle under the truck, no hint that something might be wrong. To prevent the pump gear housing from digging into the transfer case, Merchant Automotive machines its own T-6061 billet-aluminum pump gear housing, which makes use of vastly larger indexing tabs.
The bigger indexing tabs distribute the load applied to the transfer case much more evenly.
Void of the exhaust-side complexities present in VGTs, the mechanical functionality of a fixed geometry turbo is much simpler and—in most cases—a lot cheaper to overhaul or replace.
Although some low-rpm drivability is lost by switching to a fixed geometry unit, the gains in reliability, performance and peace of mind far outweigh the cost of sticking it out with a VGT that could fail at any time.While variable geometry turbochargers provide instant response at virtually any engine speed and can double as exhaust brakes, their moving parts are prone to failure.Due to being present in the exhaust side of the turbo, the vanes, unison rings and/or actuators are constantly exposed to soot, carbon and grime buildup, not to mention rust.The factory adapter is replaced with a billet-aluminum version, which makes use of a double O-ring seal on the outside of the oil pan (vs.the single O-ring seal on the inside of the factory piece).The factory New Process Gear NP261XHD and NP263XHD transfer cases offered in four-wheel drive ’01-’07 Chevy and GMC trucks make use of a gear pump within the transfer case, which forces oil to the planetary.Because the pump is driven off of the main shaft, the pump’s housing floats within the rear section of the transfer case by design.All of the above can render the moveable parts required to function inoperable, which leads to poor drivability, excessive smoke and forces the issue of cleaning or replacing the turbocharger.Any VGT-equipped engine is susceptible to this type of failure, but in the diesel pickup realm it’s highly common on ’03-’07 6.0L Power Strokes and ’07.5-newer 6.7L Cummins mills, while still being fairly prevalent on ’04.5-newer Duramax applications.Over time, this O-ring expands, swells and sometimes even breaks, allowing oil to escape.What follows is a consistent drip of oil wherever you park the truck, not to mention that the passenger side of the oil pan, starter and even transmission will wear a coat of engine oil until you solve the problem.