Fred Williams
Brand Manager, Petersen’s 4Wheel & Off Road
We used to joke that Dana 60s were Jeep axles. It seemed that as time went on and tire sizes grew, we were seeing 60s under everything. Then came along the four-door Jeep Wrangler Unlimited. With the popularity of the four-door Jeep it wasn’t long before we were seeing them highly modified. Sure, most were just getting a lift kit and some slightly bigger rubber, but some were getting the full Monty: V-8 swaps, 40-inch or larger tires, gobs of gears, and tons of added weight. We have seen JKs that outweigh fullsize pickups by a ton, literally. And the next thing you know, 60s weren’t big enough. Enter the ProRock 80.
The next thing you know, 60s weren’t big enough
Dynatrac, the purveyors of some of the finest unsprung weight money can buy, has developed the ProRock 80 to support the tires and power off-roaders dream of. We have one such project on the to-do list, and though we’re not going to divulge the whole scope of that machine we can tell you that tire size and torque will be large and reliability key.
We headed to Dynatrac’s assembly shop to learn more about the Jeep JK specific rear ProRock 80 and to build a special ProRock80 front for our upcoming bug-out truck. What we found is heavy-duty and drool-worthy.
1. Dynatrac offers a Jeep JK bolt-in rear ProRock 80 with all the suspension mounts in place. The ProRock 80 rear is a full-floating design for heavy loads and very big tires. The JK axle comes standard with eight-lug wheel ends, a selectable locker, and 4.0x1⁄4-wall axletubes.
2. The rear 80 is available with 40-spline axleshafts that dwarf the more common 35-spline ones found in most 60s. The 40-spline shafts are about 1⁄4 inch larger diameter than the 35-spline shafts.
3a. The 60 ring gear has long been the big beef with its 9 3⁄4-inch ring gear.
3b. The 80 laughs at its little brother with 11 1⁄4 inches of ring gear diameter and a 37-spline pinion shaft.
4. The ProRock 80 is a bit bigger than its little ProRock 60 brother with 1 inch less ground clearance, but the ring-gear-hugging nodular iron housing design has more ground clearance than any other axle with a 101⁄2-inch or larger ring gear. As a comparison, the ProRock 80 nodular iron housing has 1⁄2 inch more ground clearance than the average GM Corporate 14-bolt and has a ring gear almost an inch larger. With a smooth bottom that is barely 4 inches wide, it makes for a snag-free axle and not a 1-ton anchor.
5. Dynatrac also forges and casts its spindles and hub blanks. In fact, all the Dynatrac components are designed, manufactured, and assembled in the USA.
6. The axletubes in our front ProRock 80 are 4x1⁄4-wall chromoly tubing; 3⁄8- and 1⁄2-wall tubes are also available. The big tubes require special machine work to fit the inner knuckle Cs before being pressed and welded into the centersection. Dynatrac is developing an extralarge C and knuckle, which will clear 1550 steering joints.
7. Steve Flores took over the build of our ProRock 80 when it was time for gears and a locker. We optioned a 35-spline Detroit for the front axle, but we may upgrade to 40-spline later if needed. A 37-spline Dana 80 locker is also available, but the more common 35-spline axles outweighed the additional spline count.
8. Flores has years of axle building experience and has been the man behind many of the Dynatrac axles we’ve run in past projects with great results. He, along with all the Dynatrac team, is meticulous in every step of the assembly. All assemblies have a build sheet where the measurements are recorded to verify exactly how it was built.
9. After the gears are assembled and the pattern checked, a Dana gear 1410 pinion yoke was added. Our pinion angle was set at 10 degrees up with 6 degrees of caster on the steering knuckles.
10. The steering knuckles are assembled with Dynatrac’s rebuildable ball joints. Made of heat-treated chromoly components, Teflon-coated wear points, and upgraded seals for protection from the elements, these could be the last ball joints you’ll ever need.
11. Inside our axle we stuffed chromoly axleshafts that are American made. Our axles are 35-spline inner and outer, the same as a 60, but 40-spline axleshafts are a custom option if desired.
12. A big axle needs big hubs and brakes, so Dynatrac added massive 141⁄2-inch rotors and dual-piston calipers to slow down the big rig we’ll be stuffing this under. Selectable hubs are the premiere Dynalocs made of more American-made, heat-treated chromoly and stainless steel to ensure that torque transfers to the tires. In the unlikely event that these overkill hubs fail, they are designed to stay locked so you’re not walking home from the trail.
13. Want to know where our new front axle is going to reside? We’ll tell you in a future issue, but we can tell you now that it will be a 4x4 that demands strong parts and reliability for backcountry exploring.
