Pump Rub Upgrade and T-Case Brace Kit in a 2002 GM 2500 HD - Diesel World

Installing a PPE Pump Rub Upgrade and T-Case Brace Kit in a 2002 GM 2500 HD

The Duramax/Allison combo was a pretty solid homerun for the GM crowd right from the get-go when it was released in early 2001 for the 2500HD and 3500HD line-up. The Duramax engine in its first generation (2001-2004 LB7) offered great power and torque that only got better as the years went on (2004.5-2006 LLY, 2006.5-2007 LBZ, 2007.5-2010 LMM). However, the 6.6L engine needed a stout transmission to handle it. The Allison 1000 automatic that ended up bolted to the back of those engines was the perfect match, offering the industry’s first 5-spd and 6-spd automatics and offered a Tow/Haul mode that commanded early converter lock-up and later shift points to take full advantage of the Duramax horsepower and torque bands. The engine and transmission offered a solid drivetrain capable of just about anything; unfortunately, the OEM engineers overlooked a few things that if not addressed, can lead to premature and costly drivetrain failures. An internal design flaw with the pump of the NP246 transfer case that was used in 4WD models and the lack of a cross member or support for said transfer case can lead to fluid leaks, catastrophic transfer case failure, and transmission tail housing cracks and/or transmission damage.

The Pump Rub Fix

To circumvent these issues, the bright engineers of Pacific Performance Engineering, PPE, out of Fullerton, California, who have specialized in the performance Duramax market since its release in 2001, offered their expertise. Inside the NP246 transfer case used in most 2001-2010 Duramax applications, the OEM pump has five super sharp and thin tabs that can wear over time causing the oil pump to contact the rear tail shaft housing and actually create a pinhole leak. This leak, if gone unnoticed or unresolved for too long, will allow the fluid to leak out, leading many owners to drive dry, unlubricated transfer cases until they overheat, bind and explode. The simple fix to prevent all of this from happening is PPE’s custom machined pump upgrade that uses much thicker tabs to locate the pump within the housings and more evenly distribute the contact pads to eliminate rubbing through the outer case.

Cracked Tail Housings

In addition, PPE resolved the all too common problem of cracked transmission tail housings (due to the weight of the NP246 transfer case being hung off the back without additional cross members or support) in Duramax/Allison four-wheel drive models. In higher horsepower competition applications and even mild off-roading applications, the torque from the Duramax engine can be enough to put a good load on the drivelines and can lead to tailshaft failures due to the poor overhanding design. In some instances, even something as simple as a driveline being out of balance or a failed u-joint can create enough vibration in the system to break the transmission tail shaft housing. The PPE Transfer Case Brace was engineered to be bolted in above the transfer case to help distribute some of its weight to the transmission’s center section and add some rigidity to the drivetrain. Best of all, the brace can be installed without having to remove the transmission or transfer case,  requiring the most basic of hand tools. DW

1 The PPE Pump Upgrade Kit (shown installed here) replaces the factory style pump housing and uses much thicker tabs to hold it in place in the outer transfer case shell. The factory unit is prone to rubbing through the case creating a leak that can lead to major damage and complete failure of the transfer case.

2 The installation of the Pump Upgrade kit must first start by removing the transfer case from the truck. This is a job that can be done in any driveway or garage; the help of a truck hoist does make it a little easier. First, start by draining the fluid by removing the lower 15mm plug located on the back of the transfer case.

3 With the case drained, you can then remove the front and rear drive shafts. Both shafts use slip joints at the transfer case, but two straps held in with bolts will need to be removed on the axle side. A pry bar will help bump the u-joint out of the pinion. If your u-joints have any noticeable play or a lot of miles on them, now may be the right time to change them out with new units.

4 After placing a floor jack under the transmission to support its weight, the transmission cross member can be taken out. It is bolted to the frame rails with four large 18mm bolts, two on each side. The outer L-shaped bracket will need to be removed as well.

5 The cross member attaches to the transmission with just two bolts through the mid-mount. Our tech opted to remove the bolts that attached the cross member to the mount, then removed the cross member from the truck. After it was out of the way, accessing the mounts bolts that attach it to the transmission itself was much easier.

6 The next step in the removal process is to disconnect all the electronics, like this one shown plugged into the electronic shift selector. There are also a couple cables that are mounted to the transfer case that will need to be removed.

7 The last step is loosening and removing the six 15mm nuts that hold the transfer case tight to the back of the transmission. While the transfer case had previously been drained, you will still get some fluid from this once the seal of the gasket is broken, so be prepared.

8 With the help of a friend, the transfer case can then be slid back far enough to clear the mounting studs. It will need to be tipped up at an angle to slide it down past the rearward cross member. You’ll want to discard the old front gasket as a new one is supplied with the new PPE Pump Rub Kit.

9 Disassembling the transfer case further will require an internal snap ring to be opened and slid off the main tail shaft. To access this snap ring, the rubber grommet needs to be removed, along with the tail shaft speed sensor.

10 Before going further, this location of the rear case housing is where the pump will rub through. While this truck has 150,000 miles on it, the pump has not yet rubbed completely through, so luckily this “preventative maintenance” looks to have happened at the perfect time, preventing the major expense incurred when a dry transfer case explodes and sends parts flying.

11 This is the snap ring that is found inside that rubber grommet; you’ll need a good pair of external snap rings to open it up enough that the tail shaft can be slid forward enough to come loose of the snap ring.

12 With the snap ring pliers holding the snap ring open, a long flathead screwdriver can be slid in through the speed sensor port to help slide the tail shaft forward, releasing the hold within the rear transfer case housing.

13 With the rear snap ring and the rear shaft disengaged, the outer case bolts can be removed. The use of a cordless impact or air impact is going to come in handy here as these bolts are snug and will have some sealant on them, so they won’t come out easy by hand. Take note of which bolts have brackets attached to them as they’ll have to go back in the same place.

14 With all the external bolts removed, a long handled pry bar can be used on each side of the transfer case to break the seal between the two halves. Once it’s spilt apart, the rear housing can be lifted straight off, and the old gasket sealant will need to be cleaned off.

15 This shows the inside of the rear case where the transfer case pump housing rubs. This transfer case has just rolled over 150,000 miles and is definitely showing signs of rubbing. While the metal clip is still intact, by rotating it out of the way, you can see how the knife-edge-sharp pump has been pressing it into the outer case and has started to wear and round out the case. It’s only a matter of time before this would’ve worn all the way through, creating a leak and possible catastrophic failure.

16 If you’ve never seen the inside of a transfer case, they can be a bit intimidating, but swapping out the pump itself is a fairly straight forward and easy task. The pump (located on the right) will slide right off the tail shaft once the snap ring, bearing, and gear have been removed.


17 Pay attention to the stack-up position of the snap ring, bearing and gear as their positioning will need to be identical when it goes back together. The groove in the bearing will need to face rearward, as this is where the rear case snap ring will need to sit so that everything will hold together.

18 This snap ring will need to be opened up and slid upward along the tail shaft and past the splines. This turned out to be the most troublesome part of the pump kit install, as the snap ring is under a bit of tension and the snap ring pliers we had kept slipping off. But after the sixth or seventh, it passed the splines and was set aside.

19 Then the large bearing could be removed in the same fashion; it is a rather tight fit on the tail shaft, but with some finesse and wiggling it should slide right off.

20 The rear gear will then be removed; pay attention to its orientation on the shaft as one side of the gear is a stepped end and the other is flat. The gear will need to go back the same way, so the gear and bearing will seat properly.

21 To remove the pump, the pick-up tube will need to be gently pulled out of the pump and the O-ring saved. Once the tube is out of the way, the pump can then be slid off the tail shaft as well.

22 With the pump removed from the transfer case, you can finally get a good comparison between the thin stock piece (right) and the new PPE housing on the left. The new PPE unit has a much broader surface area to help distribute the load inside the housing so as not to wear through as the stock piece will.

23 The six T-15 Torn bolts can be removed from the pump and the stock housing discarded. The PPE piece can be bolted back in place of the stocker, making sure that both pump gears are left inside the pump. The bolts will be torqued to around 80in-lbs. or about as tight as a screwdriver-type handle will allow. You’ll also want to make sure that the O-ring is reinstalled into the pump to seal the pickup tube upon reassembly.

24 Once the pump, gear, bearing and snap ring are reinstalled, the pick-up tube can be inserted back into the pump and the rear case can be reinstalled. You’ll need to be sure to grab a small tube of gasket maker at your local auto parts shop to seal the cases. Make sure both surfaces are clean of the old sealant before applying a solid bead of the new all the way around.

25 Once the cases have been put back together, the outer bolts can all be installed and torqued to 27ft-lbs in an alternating pattern. This will apply an even force all the way around the cases and create a tight bond for the silicone to create a leak-free seal. The PPE kit does include a new transfer case seal to keep the mating surface between the t-case and transmission leak free as well.

26 The four-wheel drive Allison equipped GM trucks that see the abuse from off-roading, drag racing, and/or even the slightest driveline vibrations (bad u-joint, bent driveline, etc.) for too long might see premature cracks develop in the tail shaft housing of the transmission. This is usually due to the weight of the unsupported transfer case hanging off the back of that tail housing. To help prevent expensive failures, the PPE Transfer Case Brace helps distribute the weight of the transfer case to the transmission’s stronger center section and offer additional rigidity to the drivetrain.


27 The fabricated stainless steel brace has CNC laser cut brackets and 7/8” tubes for optimal strength and durability. The stainless steel brace will resist rust and corrosion from any road debris and weather and can be installed with basic hand tools without removing the trans- mission or transfer case.


28 & 29 After completing the PPE Pump Rub Kit installation and getting the reworked transfer case installed back in the truck, there are four bolts on the center section of the transmission that need to be removed and two on the top side of the transfer case. The brace simply slides into place above the transfer case and the original bolts can then be reinstalled and torqued to the proper spec. 35ft-lbs at the transmission side and 27ft-lbs on the transfer case.

Pacific Performance Engineering