The 39's are a big tire, at least for the TJ platform... That said, for my use case, I have little concern with the durability of the Dana 44 rear axle, particularly with the addition of some chromoly shafts and a full-replacement carrier such as a Detroit locker. With that in mind, my attention turnt to the front axle, the lowly Dana 30... Now, I fully understand the limitations therein, but I also
respect them. That is to say, I'm not much of a driver, but I do my best to not be abusive and I'm not too proud to take a rope or winch line. So, in what may amount to the worlds shortest, and dumbest, experiment, I'm going to see just how far I can push a polished turd(y)
The factory Dana 30 in the LJ is of a low pinion design, which technically runs on the weak side of the ring gear. Simple solution here is to find and run a Dana 30 found in pre-99 XJ's, which are high pinion. This will do a couple of nice things for me: improve the strength of the R&P interface; and provide a better front driveline angle. So, step one was to find such a beast. Czek:
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After stripping it down and starting to clean it up, I found some damage to the passenger LCA bracket that will necessitate some surgery. No big deal, as some added beef in the LCA brackets won't hurt my feeling anyway:
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With the axle stripped down, I took a few minutes to fire up the CAD machine and develop a truss:
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The other big detriment with larger tires on the LJ is the brakes. They were pretty awful in stock form, but add a few pounds of armor and rollcage into the mix, topped off with 39's, and it's downright sketchy if you have to stop in any sort of a hurry. To address this, I sourced a pair of knuckles from a 2002 Grand Cherokee WJ, which will allow me to run the 1" diameter larger WJ rotors and dual piston calipers. Additionally, these knuckles have provisions for true crossover style steering to eliminate the factory inverted 'Y' arrangement. The first step in getting these to work is to glue on some 1/4" spacers to properly index the unit bearings, as the WJ uses an odd length, compact CV axle assembly and in order to use normal shafts, you have to push the unit bearing away from the knuckle so the steering axis lines up properly. Since the knuckles and the spacers are of different caliber base materials, some pre and post-heat treatment are in order:
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Smells delicious
After post heating (read: s-l-o-w cooling), I was happy to find no cracks around the weldment areas so I think we are good to press on with this operation:
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Next up will be replacing the LCA mounts, welding out the truss on the axle housing, and then mocking up the brakes and axle shafts to ensure everything is happy. Once that's done, it'll be onto gears and then swapping it into place under the Jeep...