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Dynatrac ProRock 80 - Here's The Beef

Dynatrac Prorock 80 Center Sections
Pete Trasborg
| Brand Manager, Jp
Posted August 15, 2013

What Goes Into Building a Heavy Duty Axle

Big tires? Heavy? Low-geared T-case? Lots of gear? If any of this sounds like your Jeep, you might need a ProRock 80. While Dynatrac has been building Dana 80s for years, the ProRock 80 is relatively new. What’s the difference you ask? The Trail Series 80 which Dynatrac is calling a Pro 80 for short is like a Dana 80 but with more ribbing and strength designed right in by Dynatrac. Now a Pro 80 is not to be confused with a ProRock 80. A Pro 80 has a more “normal” profile without the high-clearance design of the ProRock 80. A ProRock 80 uses Dana 80-sized gears, but the centersection is a completely different animal with more strength, better oiling, and much better ground clearance. The Pro 80 was designed for the guy with a big truck that carries a ton of weight and fries regular Dana 60s or Dana 70s. The ProRock 80 was designed with the big JK guy in mind. It isn’t unheard of for a four-door JK to top the scales somewhere north of 3 tons. Add some armor, a pair of heavy-duty bumpers, and some big tires, not to mention all the stuff you can cram inside a JK, and the weight adds up fast. In the case of our RESQ1 project with the 800-plus-pound Miller Trailblazer 302 Air Pak, 400-600-ish-pound tire machine, tools, extra spares, and so forth, we knew that even a ProRock 60 rear might not be enough axle for us. So, we contacted Dynatrac for the only axle short of a Rockwell that would be sure to survive under the Jeep: a ProRock 80. Check out just what makes this beast of an axle the strongest, most realistic option for the street-driven trail slayer.

Step By Step

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  • 1. Top is a ProRock 44 housing, bottom left is a ProRock 60 housing, and bottom right is a ProRock 80 housing. You can see right from the beginning this is a no-nonsense proposition. And, with Dynatrac’s high-clearance design we will lose barely an inch of ground clearance as compared to a ProRock 60. That junkyard Dana 60 you are eyeballing? This ProRock 60 gives up only 5⁄16-inch of ground clearance on that axle.

  • 2. Here’s a look at ring gears. The top is an 8.8-inch-diameter JK Dana 44 ring gear which is bigger than an old school 8.5-inch Dana 44 ring gear. The middle is a Dana 60 gear which comes in at a respectable 93⁄4-inch-diameter. The bottom one is what goes in the Pro Rock 80 with a massive 111⁄4-inch-diameter.

  • 3. It all starts right here in the corner of one shop. Dynatrac has a ton of DOM and chromoly tube in stock ready to get cut to length for your custom axle. The ProRock 80 benefits from 4130 tube material whereas a “regular” ProRock 60 and smaller typically gets 1026 material.

  • 4. But the beef doesn’t stop there. The ProRock 80 was designed to carry some weight, so even the housing ends are beefier. To the left is a Dana 80 housing end. The housing ends have a bigger ID to allow the bigger axleshafts to pass through and the bearings that go into these axles make Dana 60 parts look silly by comparison. To the right is a ProRock 60 housing end. Both parts are designed and built by Dynatrac right here in the USA.

  • 5. While we are talking gears, here is another little bit of silliness. We knew that the Dana 80 pinion was bigger but while we were at Dynatrac, we put Dana 44, Dana 60, and Dana 80 gears together. We got a good chuckle out of how silly the Dana 80 pinion makes the 44 and 60 look. The Dana 44 gear on the left is a JK gear which is much bigger than an old 44 gear. The middle is a Dana 60 gear and the right is our Dana 80 gear. The ID of the smaller bearing rivals the ID of the big bearing for the smaller two while the larger inner bearing has an ID of over 2 inches.

  • 6. While wall thickness is important and does add strength to an axlehousing, bumping up the overall diameter of the tube adds even more strength. On the left is a 31⁄8-inch-diameter, 5⁄16-inch-wall tube that would typically be used in a rear semi-floating axle. The middle is a 31⁄2-inch-diameter, 1⁄2-inch-wall tube that would typically be used for a front or a rear full-float axle. To the right is the whopping 4-inch-diameter, 1⁄4-inch-wall tube that went into our ProRock 80 rear.

  • 7. While you can get a Pro or ProRock 80 built with 35-spline shafts (middle), why would you? For something with small tires that never gets locked into low range it might be ok, but we needed bigger. Shown on the right is our 1.705-inch-diameter, 40-spline axleshaft. To the left is a 1.31-inch-diameter, 30-spline Dana 44 shaft for comparison. Our massive shafts are plugged into an ARB Air Locker for the best on- and off-road performance. Again, Dynatrac uses only shafts made right here in the USA.

  • 8. If you are thinking of adding a ProRock 80 to your Jeep, you will most likely have to get your driveshaft modified. There are two pinion yoke options: 1410 and 1480. There is no way to get a smaller U-joint on the ProRock 80 just because of how massive the pinion is. We went with 1410 U-joints. The pinion nut is so big it doesn’t even fit in a 1350-series yoke as shown in the foreground. The front yoke would be used in a typical ProRock 60 while the rear is what went into our ProRock 80.

  • 9. Toting around a lot of weight means we will need a lot of stopping power to bring it to a halt. With that in mind, the ProRock 80 gets dual-piston calipers squeezing 13.8-inch-diameter vented rotors. The vented rotors should last longer than solid rotors and will run cooler too. These are the same brakes used on a J8 but the 5-on-51⁄2 bolt pattern was changed to 8-on-61⁄2 inch bolt pattern thanks to a CNC mill. The same mill also opened that center hole up to 43⁄4 inches to fit over the hub.

  • 10. Here are the two wheel hub options for the ProRock 80. To the left is the hub that went in our axle and allows us to retain the wheel sensors. The wheel sensors in a JK are used not only for ABS but also for the speedometer unlike earlier Jeeps. If you don’t need the wheel sensors, or are carrying a lot of weight, the 10K wheel hub might be for you. Dynatrac calls it 10K because it is designed for vehicles with a 10,000-pound curb weight. Or something that might see 15,000 to 18,000 pounds when loaded up.

  • 11. To cap it off, the ProRock 80 cover is even thicker than the already bulletproof ProRock 60 cover. A regular stamped Dana 60 front cover might be 1⁄8-inch-thick. The ProRock 60 cover is around 3⁄8-inch-thick. The ProRock 80 cover steps it up to 1⁄2-inch-thick. All the ProRock covers are made of nodular iron. And, like the other ProRock covers, our cover is slathered in Dynatrac’s signature silver vein powdercoating.


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