Building A Super-Strong 9.25 AAM Front Axle For Your GM Or Dodge

The independent front suspension system and 9.25-inch AAM axle delivered in 2001-2010 GM trucks is great at providing a smooth ride on the road, but when pushed hard—such is in dragging, sled-pulling, or running off-road—this axle can be less than reliable. Even if you’re not extremely hard on your truck, you may want to look into upgrading the differential for better traction. (Many trucks have open differentials in the front axle. We prefer our 4×4 trucks to power all four wheels, not just three at a time.) Several Dodge Ram trucks also rely on 9.25-inch AAM front axles and the same differential as GM, so Ram owners wanting more traction and strength than the factory differential offers can also benefit from an upgrade.

Last month we covered the build of the massive AAM 11.5-inch rear axle in our high-mileage 2001 Chevrolet Silverado 2500HD. This month we will bring you the matching buildup on the front axle. Like the work on the rear, the team at RPM Offroad in Bristol, Tennessee, handled the installation. We previously installed a long-travel Pure-Performance suspension (Diesel World, June 2011), upgrading the weak factory steering linkage in the process. But we knew that the open differential, center axle disconnect and factory CV joints could leave us stranded in the desert if we ran into problems.

1 At RPM Offroad Jason Nelson starts the installation by putting our 2001 Chevy on the lift, removing the front tires, and removing the CV axle nut behind the factory dust cover.
2 He then unbolts the inner CV joint from the differential and removes the complete CV axle assembly as one unit.
3 Comparing our previous CV axles to the new RCV Ultimate IFS CV axles, you can see that the RCV joints are much beefier than the factory units. More robust boots and seals protect the joints by keeping the grease inside where it belongs.
4­­ With the CVs removed, Nelson disconnects and secures the front driveshaft and unplugs the differential harness before unbolting the mounting hardware for the differential assembly.

What Are We Installing?

As with the rear axle, we will install a set of 4.56 G2 gears with a G2 bearing and installation kit to match the rear and compensate for the large 37-inch Goodyear Wrangler MT/R tires. The gears will spin an ARB Air Locker differential that acts as an open diff under normal operation but locks at the flip of a switch to put equal power to both front wheels.

The factory axle shafts inside the AAM 9.25 housing have been known to break under heavy loads, especially the passenger-side axle with the center axle disconnect. To remedy the axle weakness we contacted Fleece Performance Engineering and ordered a set of their TufShafts, which are made from HyTuf alloy steel. The passenger-side shaft is a one-piece design that deletes the center axle disconnect and eliminates that weak spot.

5 Next, Michael Powell helps steady the differential assembly while Nelson lowers it out of the truck using a transmission jack. A couple of strong friends can substitute for a trans jack in a pinch.
6 The passenger side of the assembly uses a center axle disconnect. This disconnect is a common breaking point of the 9.25-inch AAM IFS axle.
7 Compare the multi-piece factory axle assembly to the single-piece TufShaft from Fleece Performance Engineering. We installed one of the early TufShaft kits, which included a replacement housing for the axle. Their current design retains the stock housing but uses a single-piece shaft.
8 Normally a slide hammer is all that’s needed to remove the driver-side axle from the housing, but the retaining clip on ours was seized and it wouldn’t budge.
9 We had to have the crew at Twin City Auto Machine mill the flange off the axle shaft (see arrows) so that the case could be split with the axle shaft stuck in the differential.
10 Looking at a used factory shaft and the Fleece shaft together, the high-quality machine work is clearly visible. The Fleece shaft is built from HyTuf alloy steel to hold up to the power and abuse of sled pulling, drag racing and hard-core off-roading.

We upgraded the factory CV axle shafts with a set of custom 300M Branik Motorsports shafts when we rebuilt the suspension, but they were still riding between rebuilt factory CV joints. Since the long travel suspension allows greater CV angles at full compression and extension, we were concerned about the longevity of the factory joints. We contacted RCV Performance and ordered a set of their Ultimate IFS CV Axles built to work with this truck’s increased track width.

The RCV axle assemblies use their unique Chromoly Super Duty Dome-Mass Cage and Race at the steering end of the axle. This part is capable of handling 45 degrees of articulation with greater strength than factory CV joints. Chromoly axle shafts link the outer joints to the Pro4 Super Inboard CV joints on each side. The inner CV is protected with a rubber inner boot to keep the grease in the joint, and a rugged nylon woven over-boot to protect the inner boot from trail hazards. The outer joint uses RCV’s patented orange SST cast polyurethane dome seal to protect and seal the joint. RCV also makes their Ultimate CV axle shafts for the AAM 9.25 straight axle for Dodge Ram owners who want more strength and capability.

Performing the Installation

As with the rear axle, RPM Offroad installation technician Jason Nelson led the installation team in removing the CV axles and differential from the truck. Unfortunately, after the differential was removed, Jason realized that the driver-side axle shaft retaining clip was seized in the axle. The housing had to be sent over to Tri City Auto Machine to have the flange milled off the shaft so that the housing could be split to open the aluminum differential case. While this isn’t necessarily a common problem, it does happen from time to time and if it happens to your truck, you will need to replace the driver-side shaft. In our case we were replacing both shafts so it was only a time delay while the machining was done.

11 Before installing the new 4.56 G2 ring gear on the ARB Air Locker, Nelson cleaned the gear and mounting bolts with brake cleaner to remove any oils, then used Blue T-42 WRP thread locker on the bolts to make sure the ring gear does not come loose.
12 Nelson hand-starts all of the bolts, then torques them with a torque bar on his impact gun. Important: note that the ring gear bolts are left-hand threaded so you turn them left to tighten and right to loosen.
13 Be sure to lubricate the O-ring seals before installing them into the ARB seal housing, and make sure they do not get twisted during installation. The ARB relies on a good seal and no air leaks for proper operation.
14 The seal housing is installed on the Air Locker before the new bearings are pressed onto the differential.
15 Nelson packs the bearings with Royal Purple synthetic grease to ensure smooth operation from the start, when gear oil has not yet circulated through the housing.
16 Nelson then uses a hydraulic press to install the new G2 bearings and the pinion gear on the locker. Important: If you do not have a press, DO NOT try to hammer on the bearings! Take the parts to a shop with a press and have them do it for you.

The ARB locker requires a high-pressure air supply for activation. ARB offers several compressor options ranging from small ones designed to operate just the locking differentials to large ones capable of running air tools. We opted for the large ARB Twin compressor along with a 1-gallon aluminum tank and accessory kit. This would allow us to have air to inflate tires and run tools to work on the truck in the field. Nelson installed the compressor, tank and manifold on an aluminum panel secured to the floor of the bed on the passenger side, a placement that provides easy access to the air hose connection.

After the installation was completed, Nelson filled the differential with Royal Purple 75W-90 Max Gear synthetic gear oil. Many owners choose to use cheaper gear oil for break in since it will be changed soon, but we chose to use the good stuff from the get-go.

Tech TIP: Don’t forget to drain the oil and refill the axle after a 500-mile break-in period.

Installing the RCV Ultimate IFS CV axles is as easy as removing the factory CV axle assemblies and replacing them with the RCV units. You will need a band clamp tool to install the over-boot; RCV sells two models to do the job.

Installation of the Fleece Performance TufShafts is also pretty straightforward (provided you don’t have seized retaining rings as we did) and can be handled by an average DIYer. Installing the ARB Air Locker and setting up the new G2 gears does require more skill, however, and we recommend having your local diesel performance or off-road shop handle it for you. ARB provides great instructions for those who have the knowledge and skills to set up the gears and install the locker, but improper setup could lead to premature wear in the gears that would not be covered under warranty.

Great Results

After the project was finished we had the opportunity to put the truck through its paces at the Adventure Off Road Park in South Pittsburg, Tennessee. We were already onsite to cover an off-road race. With great traction at all four corners of the truck we were easily able to traverse steep, muddy and rocky trails through the Tennessee wilderness and get the large truck in and out of areas that others thought would be impassible. We have also run the truck in the dirt drags at Beans Diesel Performance and we were very happy with the results. If you want more strength and traction out of your IFS GM truck or AAM 9.25-equipped Dodge Ram, upgrading your front axle assembly is a great way to do it. DW

17 With the aluminum case split open, Nelson was able to remove the factory differential. Notice that despite the high mileage, the inside of the housing looks good, as do the original gears.
18 Compare the ARB Air Locker (left) to the factory open differential. The ARB locker not only distributes power to both front wheels, it can also handle more power than the stock differential.
19 Nelson carefully sets up the gear lash on the housing, making fine adjustments and verifying the wear pattern on the gears with the gear paint G2 included with the rebuild kit.
20 While the case halves were apart he drilled and tapped a hole in the passenger-side case to route the copper ARB air tube out of the housing. After the lash is finalized he applied sealant on the mating surfaces and bolted the case halves together.
21 The passenger-side Fleece TufShaft assembly is the next thing to go together. With the newer design you would reinstall the factory assembly without the internals and slide the shaft into position from the end.
22 After the driver-side shaft is properly located in the housing, Nelson gives it a tap with a dead-blow hammer to seat the retaining ring.
23 Then Nelson uses the shop air supply to do a final test on the ARB Air Locker to make sure that it engages and has no air leaks.
24 Before installing the housing back in the truck, Nelson installs the RCV Pro4 CV joint adaptors on the axle flanges using the factory bolts with Red T-71 WRP thread locker.
25 Nelson then installs the RCV axle assemblies on each side of the truck using anti-seize coating on the splines at the drive flanges.
26 Kevin Schurtz helps steady the upgraded AAM axle assembly while Nelson lifts it into the truck with the transmission jack.
27 After putting Blue T-42 WRP thread locker on the RCV-supplied Allen head mounting bolts, Nelson secures the inner Pro4 CV joints to adaptors already installed on the Fleece axle shafts.
28 Do not forget to torque the large bolt securing the RCV axle shaft to the unit bearing assembly in the hub or you could run into some serious problems on your test drive.
29 Nelson fills the differential with Royal Purple 75W-90 Max Gear synthetic gear oil.
30 To complete the axle installation, Nelson slides the RCV overboots into position and secures them with band clamps using the RCV installation tool. The overboots provide an additional layer of protection for the inner rubber boots.
31 Here’s a close-up look at the upgraded axle assembly. Those bright orange RCV dome seals will give us peace of mind as we bomb through the desert in our Chevy.
32 Charlie Holbrook programs RPM’s Torchmate plasma cutting table to cut the aluminum plates used to mount the ARB Twin Air compressor and tank.
33 The ARB equipment is mounted on the aluminum panel Holbrook cut to keep the whole assembly in one convenient location and make it easier to transfer it over when we do a short bed conversion on the truck in the future.
34 Currently the ARB air compressor panel is mounted inside the bed in the passenger-side forward corner to make it accessible without taking up too much space.
35 Nelson made an aluminum panel to house the switches in the dash slot below the A/C vent. Michael Powell installed the switch panel and wired the ARB system so that the compressor and Air Locker can be operated only when the ignition is on; additionally, the compressor must be on to operate the locker. Use care to avoid activating the locker when driving as steering will be very difficult, if not impossible, on pavement.
36 When the gear ratio is changed, the ECM and TCM must be reprogramed to maintain shift points, torque converter lockup, and correct speedometer operation. Jereme Miltier used an EFILive V2 interface from SoCal Diesel along with a laptop computer to upload the changes. If you don’t have these tools your local performance diesel shop should be able to help you out.
37 It’s a great feeling to have all four tires clawing for traction when you mash the loud pedal while exiting a turn. It’s an even better feeling knowing that the driveline will hold together under heavy abuse.

ARB 4×4 Accessories


Fleece Performance Engineering

G2 Axle & Gear

RCV Performance Products

Royal Purple

RPM Offroad

SoCal Diesel

Twin City Auto Machine

Woodward Race Products/WRP Threadlocker


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