Disconnect 30:
This axle uses a vacuum actuator on the passenger side to slide a locking collar between an intermediate shaft and an outer shaft. This feature keeps the driveshaft from spinning on the highway, thereby yielding a vibe free ride. This axle came with 260 sized u-joints (more on that later), and 27 spline shafts, just like all other Dana 30s. You can use a 95 Wrangler ABS shaft to upgrade this axle to 297/760 joints and keep the disconnect feature. Dana part numbers for this are 75589-1x for the right side and 75815-1x for the left. You can also upgrade to 297/760’s with late model non-disconnect shafts by using any TJ or XJ shafts from 95 and up vehicles, but you will need to order a special seal from Warn Industries in Clackamas, Oregon in order to seal the diff, since the old seal used to ride on the disconnect portion of the outer shaft. The weak link of the disconnect axle is rarely the U-joint once it is upgraded to 297/760 size. The intermediate shaft is fairly short in these applications, and it has a large spline section where the actuator rides. This design makes the shaft excessively torsionally stiff, causing it to break the splines on the differential side. The broken part usually sticks in the diff, forcing a complete disassembly on the trail. Pleasant. This axle is a reverse spiral unit, commonly called hi-pinion or reverse cut (more on this below).
Non-Disconnect, RS:
This axle first made it’s appearance in early XJs with the advent of the Select-Trac t-case. It does not use a disconnect, so the front driveshaft spins even in 2wd. The early axles came with 260 u-joints or an interesting CV design that tends to be pretty fragile. Sometime in the mid-90’s, the switch was made to 297/760 joints. Identical to the disconnect 30, it uses a 7.5” ring gear and 27 spline axles, and is a reverse spiral unit. Max gearing available is 4.88. Differentials and axle shafts are available to upgrade any Dana 30 to 30 spline, but a word of caution, when used in the rocks with aftermarket U-joints (more on this later), the weak link with this setup becomes the ring and pinion. This has to do with the inherent problem with the Dana 30 when used with big tires and low gearing, housing flex. When you apply torque to a pinion shaft, it tries to force the ring gear away from itself, and causing the pinion to ride up the gear teeth of the ring gear. This torque loading flexes the carrier and the housing unless both are stiff enough to resist it. With the Dana 30, the carrier takes a lot of abuse, which is why we see a lot of the 3 piece ARB carriers with broken and backed-out bolts. Eventually all this torque will weaken the ring gear and break teeth off of it or the pinion. Another weak link of this and later axles is the passenger side UCA mount. They fold like a cheap suit when abused. Do yourself a favor and weld a reinforcement plate to the front.
Non-disconnect, “Low Pinion” 30:
This axle made its debut, much to the chagrin of enthusiasts, in 2000. This axle uses geometry common to rear axles. The pinion rides below the ring gear centerline, and when used in a rear application, rides on the drive side of the gear. However, when used in a front application, the pinion rides on the coast side of the gear when driving forward. The coast side of a gear set has a greater slope to it than the drive side, so this accentuates our problem of ring gear deflection described above. When driving on the coast side of a gear, the ring and pinion is about 25% weaker than when running o the drive side. A reverse spiral gear as found in earlier XJ axles solved this problem by cutting the ring gear with the drive and coast side of the gear swapped. This design was conceived by Dana and Ford in the late 60’s to improve driveline angles and strength in their front axles. It does both well. In a sense, the 2000 and 2001 model axles are a de-evolution in technology. They do, however, all come with 297/760 joints.
A word on U-joints.
There are three common sizes of U-joints in light truck applications: the ¼ ton 260 joint which uses a 1.063” diameter cap, a ½ ton 297/760 joint which uses a 1.188” diameter cap and correspondingly larger trunion (the part that the cap rides on), and the 1 ton 332 joint which is a Dana 60 joint. The 297/760 is a strong and popular upgrade for the 260. All of these are made by Spicer corp. Lately, a slew of aftermarket joints have become available in the 297/760 size. OX, CTM, Jantz, Longfield, etc are all making joints which in one way or another increase the strength of the units. All have benefits and weaknesses, but most replace the needle bearings in the caps with bushings. This allows an increase in trunion diameter and a corresponding increase in strength. The downside is that the joints may see increased wear when driven in a vehicle that does not have hubs that unlock.
These joints should be used in high strength axle shafts such as a Warn or Superior. They can be used in an OEM shaft, but the ears of these shafts are fairly soft, and routinely rip off of shafts when using even OEM 760 joints. If you use these joints in any shaft, you must use a full circle clip to retain the cap. As axleshafts stretch, especially OEM Spicer shafts, they allow the cap to loosen and walk its way around. Eventually the little half-clip that retains them falls out and the joint is expelled from the shaft with extreme prejudice. That, folks, is what we call a show stopper. Running a full-circle clip on an OEM shaft requires some clearancing of the shaft ears to allow room for the clip. This requires actual work, which I am generally adverse to, so we used to weld the caps to the shaft. Which brings us to yet another point.
OEM Spicer shafts are like condoms. You use them once and then you flush them. The axleshaft itself rarely survives a U-joint break intact, as the four ears usually collide at a high rate of speed deforming them beyond recognition. Sometimes, though, you may think to yourself “Self, I could get a new joint in there. That Crash guy is off his rocker.” Trust me, the shaft is a goner, as it will usually be stretched and stress fractured. You may be limp it off the trail, but replace it ASAP. This is why I’ve never hesitated welding caps in, they are a permanent installation anyway. Unless you like using your condoms twice.
Two more words on shaft breaks. If you hear the dreaded “Snap, Crackle, Pop”. STOP RIGHT WHERE YOU ARE. If you drive even 5 feet on a broken u-joint, you run the risk of the shafts riding up on each other and popping the ball joints out of their sockets. If you don’t have a spare shaft with you, and you need to move, you may be tempted to pull just the outer shaft out. DON’T DO THIS ON A D-30. The Dana 30 used in TJ’s/XJ’s/ZJ’s/MJ’s/WJ’s is a semi-floating axle, that is, the shaft itself carries the weight of the vehicle. With the shaft removed, the bearings will fall apart, leaving you wheel-less.
