Merchant Automotive’s transfer case upgrade kit for ’01 to ’07 Duramax-powered Chevys and GMCs comes with a new pump housing, transfer case-to-transmission gasket, RTV silicone, blue Loctite, and a 2-quart bottle of performance transfer case fluid—all for $99.99. Merchant also offers a magnetic drain plug (red arrow) and a replacement fill plug (yellow arrow), both of which are made from 304 stainless steel. The two plugs together run $12.95. Regardless of your driving habits, Merchant Automotive recommends new fluid annually, or every 50,000 miles. Merchant Automotive’s transfer case upgrade kit for ’01 to ’07 Duramax-powered Chevys and Any time a catastrophic failure can be avoided by performing a simple upgrade, it’s worth looking into. Nickel and dime precautions taken now can save you big money and plenty of headaches later on. This month, we’re exposing a common problem found in the NP261XHD and NP263XHD transfer cases found in four-wheel-drive ’01 to ’07 Chevy and GMCs (and basically every four-wheel-drive GM from ’98 to ’07). It’s the kind of problem we’ve all grown to hate: It’s inevitable, and it surfaces without you knowing it. Perhaps the worst aspect of pump rub is that it occurs whether or not you use four-wheel drive. However, the problem surfaces faster in trucks that do a lot of city driving, as opposed to steady-state, highway driving. For our install, the recipient of the pump upgrade kit was this electronically shifted version of the New Process Gear NP263XHD, from an ’06 GMC Sierra 2500HD. Flynn’s Shop, located in Alexander, Illinois, completed the job for us in just four hours. Perhaps the worst aspect of pump rub is that it occurs whether or not you use four-wheel d Pump Rub Within the NP261XHD and NP263XHD transfer cases, a gear pump is used to supply pressurized oil to the planetary gearset and drive sprocket sleeve. Due to the pump being driven off the output shaft, its housing floats inside the rear housing of the transfer case. Over time, one of the five indexing tabs on the pump housing wears through the factory- installed anti-rattle clip (used to fill in the tolerance between the pump housing and the transfer case housing) or effectively uses it to dig into the transfer case housing. This friction is often referred to as pump rub, and it eventually leads to a small hole in the transfer case, followed by a fluid leak. But due to the location of the hole, fluid won’t escape unless the truck is moving. So the problem is hard to detect and is usually discovered after the transfer case has been damaged from lack of lubrication. Before the transfer case can be split, the snap ring that holds the rear support bearing (on the output shaft) in place has to be released. With the output shaft access plug and output shaft speed sensor removed (arrows), Flynn used snap-ring pliers and a flat screwdriver to simultaneously release the snap ring and push the reluctor gear forward (toward the front of the case). Before the transfer case can be split, the snap ring that holds the rear support bearing ( Proactive Fix With a reputation for bulletproofing virtually every aspect of Duramax-powered Silverados and Sierras, Merchant Automotive came up with a simple, affordable fix for the pump rub issue. The company developed an improved pump housing and now offers an all-inclusive upgrade kit for less than $100. Follow along as we install it in an electronically shifted, NP263XHD transfer case. Once the bearing was free of the snap ring, Flynn removed all the transfer case housing bolts and pulled the rear housing. Note that because all the work gets performed on the back half of the transfer case, it’s best to flip it up on end. Once the bearing was free of the snap ring, Flynn removed all the transfer case housing bo Taking a look inside the rear housing, we found that no damage had yet been done to the anti-rattle clip (which we reused) and saw no noticeable wear in the housing itself. This meant with only 48,000 miles on the truck, we’d caught it in time. On trucks with higher miles (usually around the 150,000 to 200,000-mile mark), the transfer case pump housing has forced the corner of the anti-rattle clip (arrow) into the transfer case housing so much that a pinhole develops. The pump housing can also eventually cut the clip in two and start grinding directly against the transfer case housing. Taking a look inside the rear housing, we found that no damage had yet been done to the an Looking at the outside of the transfer case, this is where the pinhole will develop (arrow). According to Merchant Automotive, the transfer case pump’s aluminum housing is a harder material than the magnesium transfer case housing, which is why the pump housing is able to chip away from the inside out. Looking at the outside of the transfer case, this is where the pinhole will develop (arrow With complete access to the output shaft, Flynn opened the rear support bearing snap ring just enough to slide it off the shaft. Then, the bearing was removed, followed by the reluctor wheel (what the speed sensor reads for output shaft speed). With complete access to the output shaft, Flynn opened the rear support bearing snap ring After removing the oil pump pickup from the pump body (arrow), Flynn pulled the pump assembly. For reassembly, Flynn made sure the O-ring was still installed in this oil pickup port. After removing the oil pump pickup from the pump body (arrow), Flynn pulled the pump assem Clockwise starting from the top left, you can see the six screws that mate the pump housing to the body (and require a T-15 Torx bit), the reluctor wheel stacked on top of the rear support bearing and snap ring, the fluid magnet, the factory pump housing, and Merchant Automotive’s billet-aluminum housing. Clockwise starting from the top left, you can see the six screws that mate the pump housin Here you can see the difference in indexing tabs between the Merchant Automotive housing (left) and the factory housing (right). The larger tabs distribute load much more evenly and won’t grind the anti-rattle clip into the transfer case housing. Merchant’s upgraded housing is CNC-machined from aircraft-grade T-6061 aluminum. Here you can see the difference in indexing tabs between the Merchant Automotive housing ( Flynn cleaned up all the reusable components by hitting them with brake cleaner and then drying them. Then the pump gears were pre-oiled for initial lubrication. Flynn cleaned up all the reusable components by hitting them with brake cleaner and then d Next, the new pump housing was installed on the pump assembly. The supplied Loctite was applied to the six housing screws, and they were tightened diagonally to ensure the housing mated evenly to the pump. Each screw was torqued to the recommended 80 in-lb. Next, the new pump housing was installed on the pump assembly. The supplied Loctite was ap Reinstalling of everything was straightforward. First, the pump assembly was lowered back down on the output shaft, and the oil pickup tube was reattached to the pump body (arrow). Then the reluctor wheel was installed, followed by the support bearing and snap ring (not shown). It’s important to remember that the reluctor wheel (shown here on the output shaft) must be reinstalled with its stepped edge toward the pump. Reinstalling of everything was straightforward. First, the pump assembly was lowered back After cleaning up both mating surfaces on the transfer case halves, the supplied silicone sealer and dispensing nozzle was used to run a bead around the perimeter of the bottom half of the transfer case. From there, Flynn located the alignment dowels in the front half (on bottom in this case) and slowly lowered the rear housing onto it. After cleaning up both mating surfaces on the transfer case halves, the supplied silicone All housing bolts were hand-tightened and torqued in a diagonal pattern to 45 ft-lb. Merchant’s magnetized drain plug was also installed at this time. All housing bolts were hand-tightened and torqued in a diagonal pattern to 45 ft-lb. Merch With the snap ring reinstalled and the support bearing locked in place, the output shaft access plug was reinstalled, as was the reluctor wheel speed sensor (shown). Flynn used some silicone sealer on both the rubber plug and the sensor’s threads for a leak-proof seal. Being that the speed sensor is plastic, tightening it just past snug with a 3/4-inch wrench is sufficient. With the snap ring reinstalled and the support bearing locked in place, the output shaft a Prior to installing the transfer case, Flynn removed all gasket material residue from the Allison 1000’s tailhousing. Notice the two bolts missing (arrows) where the tailhousing connects to the main case of the transmission (there are two missing from the other side as well). This is because we were installing one of Merchant Automotive’s transfer case braces. Prior to installing the transfer case, Flynn removed all gasket material residue from the Merchant Automotive’s transfer case brace ties it to the tailhousing of the Allison transmission. Its purpose is to prevent the tailhousing from cracking due to driveline vibration, which can result from a bent driveshaft or failing U-joint. The support is made from 7⁄8-inch-diameter, 0.120-inch-wall DOM tubing; the plating is 1/4-inch thick; and all units are powdercoated orange. The brace (which can only be installed with the transfer case in place) mounts using four bolts in the Allison’s tailhousing and two bolts in the top of the transfer case housing. Merchant’s brace retails for $149.99. Merchant Automotive’s transfer case brace ties it to the tailhousing of the Allison transm SOURCES Merchant Automotive 100 N Fairview Rd Suite 30 Zeeland MI 49464 866-399-7169 www.merchant-automotive.com Flynn's Shop Alexander IL 217-478-3811 By Mike McGlothlin Enjoyed this Post? 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