It’s no secret that when a manufacturer builds a vehicle, it’s actually nothing more than a series of compromises. Engineering wants one thing, but production demands another, legal something else, and finance just says no to it all. That’s how we as enthusiasts get the opportunity to upgrade parts. A quick and easy way to add performance and styling is by swapping out the fluid pans, which, in the case of our Silverado 2500HD, includes the oil pan, transmission pan, and rear differential cover. Pacific Performance Engineering, better known simply as PPE, offers a solution for all of these. Follow along as we install PPE’s entire cast-aluminum pan catalog.
The factory oil pan leaves a lot to be desired. Its biggest fault lies in the stamped valley, which prevents nearly a quart of the engine’s dirtiest oil from being drained during oil changes. Fortunately, PPE’s high-capacity Duramax oil pan is the solution. Made in the USA from cast aluminum, the pan holds an extra quart of fluid, dissipates heat better, acts as a sound damper, and allows for the oil to be drained completely. The pan also removes restrictions around the oil pickup, which results in more consistent oil pressure and better lubrication. The pan accommodates both two- and four-wheel-drive vehicles and can be installed with the engine in the chassis.
| The factory stamped-steel lower oil pan is quite the sight to behold. Why engineers choose to place certain indentations in the places they do will forever be a mystery to us. We’re sure they have their reasons, however.
| Since we had our LB7 Duramax out of the chassis for a rebuild, we decided this would be the best and easiest time to install PPE’s aluminum lower oil pan. Once the factory lower pan is detached, there are two studs in the upper pan that need to be removed. Since the studs are threaded into the upper pan, a pair of pliers made quick work of the job.
| Located inside the lower oil pan is the low oil level sensor. The PPE pan has provisions for reusing the factory sensor. The first step in transferring the unit is to press the plug through the hole in the side of the pan. This plug seals with an O-ring and is held in place by a clip on the outside of the pan.
| The sensor housing itself is bolted to a pedestal that is cast into the pan. Use caution not to overtighten these bolts.
| The lower oil pan is sealed to the upper pan with a bead of silicon. We applied the same gray Clevite silicon we used to seal the rest of the engine’s critical surfaces, but any high-temperature sealant will work.
| Once the silicon was applied, we carefully lowered the pan into place, ensuring the sealant wasn’t displaced in the process.
| PPE replaces the factory bolts with Allen head fasteners. We started all the bolts by hand before tightening them mechanically. It’s worth noting that if you’re doing this install with the engine in the chassis, you’ll want to snug two or three of the bolts first to aid in holding the unit in place.
| Extensions and a 3/8-inch-drive 6mm Allen socket are critical to ensuring the install goes smoothly. Without these tools, it will be somewhere between frustrating and impossible to properly tighten all the bolts.
| PPE’s aluminum oil plan fits perfectly in the chassis of both two- and four-wheel-drive vehicles. The transmission fluid cooler lines are a tight fit, but they retain plenty of clearance. As mentioned previously, the pan can be installed with the engine in the chassis by removing the crossmember that spans below the pan (seen here).
The Allison 1000 is a phenomenal transmission. However, all good things can be improved, and that’s just what PPE’s heavy-duty transmission pan aims to do. Available in two sizes, standard and deep, these pans are constructed of cast aluminum and are equipped with two threaded ports for gauge sensors and a high-power Neodymium magnet drain plug, and allow for the retention of the factory reusable gasket. We opted for the deep pan, which adds 4 quarts of fluid capacity. This extra fluid, along with large ¾-inch cooling fins on the outside and heat sink fins inside, have been shown to reduce operating temperatures by as much as 40 degrees.
| The Allison 1000 transmission is fantastic by all accounts. However, its stamped pan leaves quite a bit to be desired. Fortunately, companies like PPE have addressed these with replacement cast-aluminum pans.
| Before doing anything else, the transmission needs to be drained of its fluid. Fortunately, the Allison transmission has a drain plug—unfortunately, it’s recessed…more on that in a moment.
| With the fluid drained, the 12 mounting bolts can be removed. As you get down to the last bolts, it’s critical to support the pan with a free hand, assistant, or transmission jack. The pan needs to be lowered straight down slowly.
| And here’s why it’s critical to lower the pan slowly…despite draining the recessed plug, more than 2 quarts of fluid are left in the pan. If you’re not careful, these can end up coating your driveway or worse.
| PPE offers a couple different versions of its Allison transmission pan; we opted for the deep variety that holds an additional 4 quarts of fluid than the factory version. Note the addition of cooling fins, temperature probe ports, and a flush-mounted drain plug on PPE’s version.
| On the inside of the pan are a series of cast fins. These fins aid in heat dissipation, drawing heat to the cooling fins on the outside of the pan, and act as baffles as well.
| Included with the pan is a new internal filter element. To remove the old filter, simply pull straight down. You’ll also want to ensure the orange O-ring is removed from the valvebody before installing the new filter. Beware, the filter and valvebody also contain fluid that is waiting to drench you and anything under it upon removal. You’ve been warned.
| The Allison 1000’s pan gasket is a reusable steel and rubber unit. We gave ours a quick wash, inspected it for damage, and then reinstalled it on the new pan. You’ll want to use a bolt or two as guides to keep the filter in place while situating the new pan in the transmission.
| Once all the bolts have been started by hand, they can be torqued to the required 15 ft-lb. You’ll need to use a crisscross tightening pattern to ensure even pressure on the gasket.
| With the installation complete, it’s time to refill the transmission with fluid. We opted for Amsoil’s Signature Series fully synthetic automatic transmission fluid. Due to the pan’s increased capacity, we poured in nearly 14 quarts of fluid. Thankfully, Amsoil sells it in gallon jugs.
| Functional bits aside, PPE’s deep transmission pan looks dead sexy as well.
Rear Differential Cover
Form and function describe PPE’s AAM 11.5 rear differential cover. Also known as the GM Corporate 14-bolt, the axle’s differential cover is visible from the rear of the truck, so dressing it up becomes top priority for owners. Cooling fins are found both inside and outside the cast-aluminum cover, and an additional 1.5 quarts of fluid capacity help keep things cool.
| Found under most ’01-and-newer Silverado 2500HD and 3500HD pickups, along with ’03-to-current Dodge/Ram 2500 and 3500s is the AAM11.5 full-floating rear axle. Known as the corporate 14-bolt in GM circles, this axle is incredibly stout, however, its Achilles heel is the stamped-steel cover.
| Installation of PPE’s cast-aluminum cover begins easily enough with the removal of the 14 retaining bolts. Since these axles use a gasket instead of silicon to seal them, be ready with a catch pan, as fluid will begin seeping out immediately.
| With all but two upper bolts removed, you can give the cover a little pry to slowly drain the fluid. This ensures a controlled release of the old fluid, instead of a sudden dump.
| Now is a good time to give the rear axle gears a quick inspection. Look for abnormal wear marks, chipped teeth, or signs of water intrusion.
| Once the old gasket is completely removed, the mating surface can be cleaned of any residual oil by wiping it with brake cleaner and a rag. We used a wire wheel to remove the old gasket, but any non-destructive method of your choosing can be used.
| A new gasket is provided with the cover and needs to be installed with the writing facing up. Also seen here are the internal casting fins that help dissipate heat from the gear oil. The cover also comes with fill and drain plugs and two pre-tapped ports for temperature probes.
| Before the new cover can be installed, the factory parking brake bracket needs to be trimmed. Following the diagram in the instructions, we placed the bracket in a vise and made the necessary cuts with an angle grinder.
| After all the bolts were started by hand, we proceeded to torque them to the required 15 ft-lb in the crisscross pattern required. New Allen-head bolts are provided and a 3/8-inch-drive 6mm Allen socket is still your best friend.
| PPE provides a nice big fill port on the front of the differential cover. While squeeze-bottle-type gear fluids would fill directly from the bottle, we needed to use a pump to top the differential off with the required 5 quarts of Amsoil Severe Gear 75W-90 fluid.
| Aside from the improved appearance, the PPE heavy-duty rear differential cover provides added protection from impact, holds nearly 2 extra quarts of fluid, and helps keep that fluid cooler under heavy use.
High-Capacity, Cast-Aluminum Oil Pan
Heavy-Duty, Deep-Cast Aluminum Transmission Pan
Heavy-Duty, Cast-Aluminum Differential Cover
Amsoil Signature Series ATF
Amsoil Severe Gear