Owners of four-wheel-drive General Motors pickups from 1997 to 2010 should all be aware of the dreaded "pump rub" issue. It doesn't matter if you drive a Silverado 1500, Sierra 3500, or even an Avalanche, if your truck has a transfer case, this story is for you.
In short, the pump rub issue refers to when the fluid pump inside the transfer case wears a hole in the case itself. GM transfer cases use a gear-driven pump inside the case that is driven off the mainshaft. Because of this design, the pump must "float" in the rear case half. There are four tabs around the edge of the pump that are used to locate it in the housing. GM installed a steel spring clip in the housing to try to prevent wear, but over time this clip can itself wear out or even break. This leads to the aluminum pump wearing through the softer magnesium housing.
The resulting hole can cause a very small leak. Because of the pump's position in the case, this leak is typically quite high on the case, meaning that it only leaks when the truck is in motion and does not leave a telltale puddle under the truck. Ultimately, afflicted trucks will run the transfer case dry of fluid before the owner has any idea that something is wrong.
Thankfully, there is a solution. PPE Diesel offers a kit that comes with a new pump housing cover, transfer case to transmission gasket, and threadlocking compound for less than $70. This new pump cover is machined from billet aluminum and features much larger locating tabs. This removes the need to use the factory spring clip and effectively prevents the dreaded rub from occurring, potentially saving thousands of dollars in repair costs.
The task is pretty straightforward for anyone with a bit of mechanical ability and takes just a few hours from start to finish. In addition to what you'll find below, there are many great videos on the internet that walk through the process in great detail.
| The first step in installing PPE's GM pump rub kit is to remove the transfer case, naturally. Depending on the year and model of truck you're working on, the process will be slightly different. However, the driveshaft will need to be removed from all trucks and set aside. You'll also want to drain any remaining fluid prior to removal.
| Installing the pump rub kit is fairly straightforward as long as you have a bit of mechanical aptitude and a good set of snap ring plyers. You'll also need a set of metric wrenches and sockets, a Torx bit set, and also a torque wrench.
| While the procedure can be completed on a workbench, a fixture like the one shown will make life easier. If you plan to install more than one, we definitely suggest it.
| The process beings by first removing the output shaft speed sensor and the rubber snap ring grommet in the tail shaft housing. Next, insert you snap ring plyers and release the snap ring that retains the output shaft. Using a flat blade screwdriver, place it through the speed sensor hole and press up gently on the tone ring. This will release the output shaft.
| Next, remove the bolts holding the transfer case halves together, noting where clamps and retainers go. The case halves are held together with RTV sealant, so a light tap with a dead blow hammer is a quick way to release the bond.
| Seen here is the factory anti-rattle clip. One some older cases, such as ours, it can be found in the housing held in place with a magnet. Newer cases tend to have the clip secured to the pump. And in the worst case, the clip is broken, and you'll be cleaning shards out of the transfer case.
| Now is the time to clean the magnet that resides below the fluid pickup tube. This magnet helps to catch any of the metal bits that might otherwise be floating in the oil. If you're installing magnetic drain plugs, it's OK to discard this one.
| Next up is removing the output shaft bearing retaining snap ring. With the ring detached, you can remove the output shaft bearing, the tone ring, and finally the oil pump.
| Shown here are the removed transfer case pieces, along with the new billet aluminum PPE pump cover (right).
| Removing the factory pump cover requires the use of a T-15 Torx bit. Hand tools are your friend here, as a stripped or broken bolt can spell disaster.
| With the bolts removed, the factory pump cover can be lifted off of the pump housing. Make sure both pieces of the pump remain together. Oftentimes one sticks to the pump cover and can get unknowingly discarded.
| The billet aluminum PPE cover installs in exactly the reverse order of removing the factory piece.
| Be sure to use a dab of threadlocking compound on the pump bolts during reassembly. PPE includes the needed threadlocker in the kit.
| Using a -inch drive ratchet and T-15 Torx bit, the pump cover bolts are snugged hand tight.
| One of the things that PPE tech Drew likes to do while installing pump rub kits is to fill the transfer case with a bit of fluid before closing the case. While not necessary, this ensures that there's fluid in the transfer case and eliminates some of the time spent pumping fluid into the tiny fill hole after it's back in the truck.
| With the new PPE cover on the pump, the unit can be lowered back onto the output shaft. Ensure that the O-ring is firmly in place before reattaching the oil pickup tube.
| Next, the tone ring is reinstalled on the output shaft. Note, the side with two stepped grooves faces down toward the pump.
| Finally, with the output shaft bearing in place, the snap ring can be reinstalled.
| From here you're ready to reinstall the rear case half. Note that by this point we've already cleaned the old RTV sealant off of the mating surface with a Scotchbrite pad.
| New RTV sealant is applied to the case halves prior to reinstallation. This ensures leak-free operation for many years to come.
| Wrapping up the install, the rear case half is lowered into place and bolted together. The output shaft snap ring gets reinstalled in the reverse of how it was removed, and finally the rubber plug and output shaft speed sensor are reinstalled.