1971 Chevy Suburban Currie Axle Swap - Project Superburb: Iron Jock 60 Assembly

Picking up where we left off, the new Iron Jock 60 housing was ready and waiting for knuckle assembly and installation of internals such as the differential and axleshafts. Here you can see the Currie technician measuring the housing to determine axleshaft length.

All Currie axleshafts start out as a raw forging of 4340 chrome-moly material as shown here. Each shaft is cut to length on a chop saw, then each is placed in a special grinding tool that machines the final outside diameter of all bearing and seal surfaces.

Once an axleshaft leaves the grinding machine, Currie's splining technician readies the shafts for the spline-cutting tool. Our shafts were spec'ed out as 35-spline; however, the same computer-controlled machine can cut any spline count a customer needs, and with a simple calibration change, the tool can be reconfigured to cut virtually any spline count. The spline cutter utilizes a spinning tool bit with a series of special cutting blades that create the proper pressure angles necessary for a particular spline design. As each spline is cut, the machine rotates the shaft to position the cutting head for the next pass.

Randy's Ring & Pinion supplied us with a 4.88:1 gearset to match the rearend of our Suburban. We love working with Randy's because they always seem to have the right part in stock when we need it, and thanks to a healthy distribution system, they can typically get the parts to us the very next day.

Eaton sent us a trail-proven Detroit Locker to use for this project. We picked this differential because they rarely, if ever, fail. The design utilizes robust internal parts to ensure that 100-percent traction is delivered to both drive wheels whenever torque is applied. The Detroit Locker automatically allows wheelspeed differentiation when needed. This enables the inside wheel to track around a corner at a slower speed than the wheel on the outside of the corner.

Once the ring and pinion parts were installed along with the Detroit Locker, the Currie technician set up a gear pattern to spread drive torque out evenly over the middle of the teeth. This pattern will contribute to long wear life and noise-free operation.

One of the things that sets the Currie Iron Jock axle assembly apart from other aftermarket Dana 60 designs is the use of a larger front pinion support bearing. The bearing on the right is the size used for both the front and rear pinion support bearings, whereas the bearing on the left is the size commonly used in the front of virtually all stock and aftermarket Dana 60 housings.

Currie utilizes this machined bearing spacer to enable the smaller front end of the pinion to fit properly with the larger bearing mentioned above.

Here you can see the front pinion bearing prior to the installation of the pinion seal. Notice the oil channel (arrow) that feeds gear oil to the front side of this bearing. When operating, oil is pumped up to the front side of this bearing by the ring gear. With this design, oil must flow through though each of the pinion support bearings to complete the lubrication circuit.

We secured a pair of Yukon's Dana 60 Super Joints to further strengthen our front drive system. These U-joints were machined from a solid chunk of through-hardened 4340 steel and then treated with a titanium nitrate coating (the gold color), giving it super-high-wear characteristics. This allows the cross to ride directly in the induction-hardened 4140-chrome-moly caps with very tight clearances and without a separate bushing or needle bearings. Lacking separate cap bushings or needle bearings, the trunnion is larger in diameter as well, adding to overall strength. The trunnion on the Super Joint is some five percent larger than a traditional Dana 60 U-joint (0.935 versus 0.892 inch). A special 200,000psi compressive strength copper-based grease is included with the pair, along with a compact and very handy grease gun. Yukon says that this is the only grease you should use with the Super Joint.

Randy's Ring & Pinion also set us up with a pair of 35-spline 4340 steel stub axles for this project. These shafts provide an excellent value in terms of strength per dollar spent. Sure, we could have sourced ultimate-strength 300M stub axles, but for our needs, 4340 should survive just fine.

Our friends at Boyce Equipment sent us an assortment of parts needed to complete the buildup. These Chevy-style Dana 60 spindles, along with all the necessary bearings and locking spindle nuts, made the process of final assembly a snap.

In addition to the front spindles and bearing parts, Boyce Equipment supplied us with Chevy eight-lug brake rotors preassembled with hubs and lug studs as shown here. Boyce offers these parts directly through their website or by phone. In most cases, the parts are regularly stocked and ready to ship anywhere in the country as needed.

Randy's Ring & Pinion supplied us with two Chevy kingpin rebuild kits for our Reid Racing knuckles. These roller bearings are what carry the entire weight of the front of the truck. We like this design better than the new-style ball joints use by OEMs because these are rebuildable and offer significant gains in strength.

The only parts we forgot to order from Randy's were these Spicer lower kingpin caps. A quick call to Parts Mike, a leading supplier of axle-related parts and equipment, was all it took to get the overlooked parts and ensure that we could finish up the photo shoot on the following day.

With the knuckles, spindles and caliper brackets mounted in place, the Currie technician installed the new disc brake rotors and bearings to the assembly.

Boyce Equipment also supplied us with all the remaining front brake parts we needed to complete the build. These off-the-shelf Dana 60 calipers are typically found on '75 Chevy 1-ton pickups. In addition to the individual axle parts Boyce supplied to us for this project, Boyce offers complete Dana 44, 60, 70, and 80 assemblies ready to fit under your full-size pickup or SUV.

This is the sacrificial differential skidplate that Currie installs to the bottom side of each and every Rock Jock and Iron Jock 60 axle they build. These skidplates are made from abrasion-resistant AR400 steel material-the same material used on bulldozer blades and backhoe buckets. The idea is that this bolt-on skid will take the abuse so that the cast-iron center section does not have to. We like that they can easily be replaced as needed by simply removing four Allen bolts.

This is the standard stamped-steel differential cover Currie includes with all Iron Jock 60 axles. Also available as an upgrade option, Currie offers a thick version of this cover, which allows additional weld surface for custom fabrication of link mounts and/or hydraulic ram setups.