Almost exactly a year ago we chronicled just about every step in building a Dana 60 front axle at home, (“Some Assembly Required,” Sept. ’12). Since that article was published, we wrangled the axle under our TJ, and it has performed flawlessly during numerous grueling off-road adventures. The front axle replaced a badly bent and abused Dana 30 and was a welcome strength upgrade, but we soon realized that our more aggressive driving style (thanks to no longer having a grenade in the front end) had the Ford 8.8 rear axle we had swapped in years before living on borrowed time. After having some ring gear bolts back out and almost take out the rear axle, the decision was made to start gathering parts to do a similar Dana 60 upgrade in the rear.
We had picked up a freebie full-float Dana 60 rear from a ’78 Ford F-250 several years earlier for another project that was scrapped, so we already had a suitable donor. There were several problems, though: It was too wide, it was eight-lug (we built our front Dana 60 with 5-on-5 1⁄2 bolt pattern), and it had puny 1.31-inch, 30-spline axleshafts. Plus, as it turned out, it was a total disaster on the inside. No wonder it was given to us.
Being the typical cheap bastards that we are, we decided to build the axle at home and farm out only the housing modifications, primarily because you really need a fixture in order to do the housing modifications the right way, something we don’t have at home. Though we built this axle for a TJ, the same basic steps apply to building any custom rear axle. In the end, we have an axle that cost about a third of what it would if we had simply called a custom axle builder and ordered it, and we learned quite a bit along the way. With our axles sorted out, we can hit the throttle sooner and stay in it longer without fear of breaking or generally becoming a trail-blocking idiot, but all we’re doing is moving the fuse to the next weakest link in the chain. But that’s part of the fun, isn’t it?
Why on Earth Go From Full- to Semi-Float?
Many of you are probably reading this and wondering if our childhood diet consisted of eating paint chips. Why would someone take a perfectly good full-floating axle and convert it to semi-float? There are several reasons, but first, here’s a quick rundown of the difference between the two.
With a full-floating axle, the weight of the vehicle is supported by the spindle, and the axleshafts’ only jobs are to transfer engine torque from the differential to the wheels, while the shafts in a semi-floating axle must both support vehicle weight and transfer engine torque. By design, a full-floater is stronger, particularly in heavy-duty applications where there’s a lot of weight involved. This is why you see full-float axles used on everything from dump trucks to 18-wheelers, in addition to 3⁄4- and 1-ton trucks, while semi-float axles are more common on lighter applications.
We originally planned on keeping the full-floater and converting it to 5-on-5 1⁄2 (almost all full-floater axles are eight-lug), but it turns out that’s not as easy as it sounds. While it is technically possible to drill the hubs the center of the hub must also be machined down so the 5-lug wheel will slide over the hub. So much material must be removed that there’s not a whole lot of meat left, meaning that you end up with a weak wheel hub. There are aftermarket versions that might be stronger, but they’re also expensive. Next, brakes can get complicated. Drum brakes are heavy and less than ideal in mud, and generally aren’t as good as disc brakes, but there are no clear cut solutions to converting to disc brakes. Those that do exist involve a fair amount of mixing and matching parts. Then there’s the axleshafts themselves. The most common Dana 60s found in junkyards are 30-spline, which really aren’t much stronger than the equivalent Dana 44 shaft. So if converting to 35-spline is a priority (and it should be), then you’re still stuck buying axleshafts and possibly boring the spindle to get the bigger shafts to fit. Lastly, width is a factor. Since full-floaters are found in fullsize trucks, they’re generally going to be wider than Jeep width, so the housing must be narrowed. Now you’re talking about more modifications, and before long, you’ve got a completely custom axle with a bunch of one-off parts that are not readily available if you break down in the middle of nowhere.
For all of these reasons, we chose to go semi-float. The axleshafts we used are off-the-shelf aftermarket 35-spline pieces for 5-on-5 1⁄2 and 5-on-4 1⁄2, so we solved the spline and bolt pattern issues in one shot. Second, the big bearing “Torino” style housing ends we used will accept our existing Ford 8.8 backing plates, rotors, and calipers, which solves the brake issue. Even if we didn’t have Ford 8.8 brakes on hand, all of these components are readily available at any junkyard (Ford Explorers litter yards all over the country). And last but certainly not least, this axle is destined for a lightweight rig, so weight is much less of an issue. Keep in mind that factory semi-float Dana 60s exist, and there may even be some rare application we’re not aware of with the right width for a Jeep, but the vast majority are an undesirable C-clip design. With the press-on axle bearing style like we chose, short of the shaft snapping right at the axle flange (an extremely rare occurrence, but it does happen), we can still limp off the trail if we manage to break a shaft.
Step By Step
1. It turns out that our free donor axle had spent many years in a pasture before being offloaded on us. The inside had a thick coating of rust-colored goo and chunks of who knows what. We were so sketched out during disassembly that we neglected to take photos of the inside, but it looked much like the condition of the leftover parts you see here. No amount of brake cleaner was going to get it clean, so we wisely sent the housing out to be sandblasted after we completely gutted it, which set us back about $40. Money well spent. We even burned the clothes we were wearing during disassembly rather than contaminate our washing machine.
2. Arizona Differential did such a great job on our front axle that we turned to the company once again for the necessary housing modifications on this project. Our freshly sandblasted housing looked brand new and made working on it much easier. The company first set up its fixture, which included this plate that indicates axle centerline, machined pucks for the carrier bearings (also visible) and housing ends, and a solid rod that slides through the center of all the pucks.
3. Our trial measurements told us we’d be cutting it close with our 65-inch goal, and it turned out we had a right to be concerned—our donor housing was 1⁄2-inch short of being able to achieve this width. To maximize what length was there, technician Justin Draper cut the housing as close as possible to the welds for the original spindles. He used a chop saw and a special fixture built just for cutting down housings.
4. The housing ends we chose are aftermarket versions of factory Ford 9-inch ends that accept Set 20 axle bearings, also referred to as “Torino” or “big-bearing” ends. The ends were designed to slip inside a typical Ford 9-inch housing, which has much thinner axletubes than our heavy-wall Dana 60. As a result, Draper had to cut off a lip machined on the ends using a lathe. This lip is really just for indexing and has no impact on overall strength.
5. These spindles are what make a full-floating axle a full floater. The wheel hubs ride (via bearings) on these spindles, so the weight of the vehicle is carried by the axlehousing rather than the axleshafts. If we were sticking with an eight-lug wheel bolt pattern, we likely would have kept the full-floating design, but a combination converting to 5-on-5 1⁄2 pattern, upgrading to 35-spline shafts, and brake simplicity led us down the semi-float path (see sidebar on page 62).
6. After doing some research, we discovered some off-the-shelf axleshafts from Ten Factory that would work perfectly for our application. These chromoly shafts are pre-drilled for 5-on-5 1⁄2 and 5-on-4 1⁄2 bolt patterns and are 1.5-inch-diameter, 35-spline. They measure 31.5 inches long, which turned out to be perfect for our goal of 65-inch width between wheel mount surfaces.
7. The 35-spline ends are extra-long, which enables the shafts to be shortened for custom applications. This turned out to come in handy.
8. With the housing prepped and ready to go, Draper inserted the large alignment bar in the housing and through the pucks under the carrier bearing caps seen earlier. Similar pucks were placed in the housing ends and also slid into place. The housing ends must be aligned perfectly. If not, the axle will eat up bearings, ruin axleshafts, and cause the diff to go all squirrely. This is why it’s important to leave housing modifications to the pros.
9. Once lined up, Draper tacked each housing end in four places, while Arizona Differential owner Nate Warren rotated the aligning bar to ensure that the ends didn’t draw out of alignment from the welding heat. After both ends were tacked, all measurements were double-checked one last time before cranking up the welder from “stun” to “kill” and burning them in permanently. The alignment bar stayed in place throughout to ensure nothing got out of whack.
10. As mentioned, our housing ended up being 1⁄2-inch shy of our 65-inch goal, so the axleshafts had to be shortened to match. Cutting a hardened shaft isn’t easy, as they would ruin the blades of most traditional saws. Draper cut them using a regular chop saw and then beveled the edges using a bench grinder. This didn’t hurt the splines at all, and thankfully the Ten Factory shafts have extra-long splines in case the shafts need to be cut. We could have avoided this by using another housing, but we were too far into the project by the time it was discovered the housing was shorter than ideal.
11. ack at the home shop, we cut off the original spring pads and shock mounts on the housing in order to start positioning the TJ mounting brackets. We ordered a complete set of axle brackets from Rusty’s Off-Road. These brackets are laser-cut from 3⁄16-inch steel and are pre-formed to accept TJ control arms as well as the rear track bar. They are even set up to place the brackets at the proper angles in relation to the housing, which takes out a lot of guesswork.
12. We measured several times, tacked the brackets in place, and then measured again. Double and triple check everything! In our case, we missed the spacing of the lower control arm brackets the first time, so we had to knock them off and start over. This is why you measure at least twice and weld once.
13. Though we had the housing sandblasted, a look down the axletubes revealed plenty of mung still present inside. One of our friends came up with this ingenious solution. We bought a cheap 3-inch-diameter wire wheel and welded it to a 3-foot length of 3⁄8-inch solid rod, chucked it up in a drill, and went to town. Quite a bit of nastiness was removed as a result, which could have otherwise contaminated our new gears. Always do a thorough cleaning when performing gear work, and that includes the axletubes.
14. With the housing mods out of the way, we could turn our attention to the business end of the axle: the gears and locker. For the gears, we turned to Motive Gear for a standard-rotation 4.88 ring-and-pinion, as well as one of its master rebuild kits. Motive is well known for producing quality gearsets, and this one proved to be no different. For the locker, we chose a Detroit Locker to match the front axle. The author prefers Detroits for their strength and simplicity. They’re not quite as smooth on the street as an open differential, but they’re fairly bulletproof and you won’t ever forget to turn one on when you hit an obstacle.
15. What we thought was going to be one of the biggest hurdles in this project turned out to be one of the easiest. The big-bearing 9-inch housing ends happen to be identical to the ends on the Ford 8.8 were running, so we were able to re-use all of the brake components from our existing 8.8 rear axle (minus the wheel spacer). The backing plates, caliper stands, and rotors literally unbolted from the old housing and bolted on the new one. Even parking brake functionality is maintained, and replacement parts are readily available.
16. We’ve covered setting up TJ axle brackets in several past issues, so we’ll just hit the highlights. After finding the axle centerline and setting the housing at the proper pinion angle for your application, measure the angle and distance of the brackets on the original axle and transfer them to the brackets on the new housing. We had to massage the radius of the Rusty’s Off-Road control arm brackets a little to match the larger diameter of the Dana 60 axletube, but otherwise the brackets went on smoothly. Setting the pinion angle is an important factor here, so if you’re doing other major modifications, such as changing lift height, it might be best to leave the brackets tacked in place until the axle is set up under the vehicle.
17. We splurged on some new rotors from our local parts store but we did need to make one modification: Explorers use a 5-on-4 1⁄2 bolt pattern, so we had to drill them to 5-on-5 1⁄2. Luckily, our dual bolt-pattern axleshafts served as a handy template for drilling the rotors. We simply bolted them to the axleshafts backwards as shown and used a center punch to mark the location of the new holes, then removed the shafts and drilled them. Crude, but effective. Most machine shops can drill rotors for a small fee.
18. Sometimes it’s the little things that get you, and this one was at least a 4-hour time suck. The axleshafts didn’t come with wheel studs, and we tried three different sets of studs but none of them were right. We ended up calling Ten Factory for the part number for the right studs, but it would have been really handy if the shafts had simply come with them, even if the shafts had cost a little more. For reference, the Dorman part number is 610-235, which nets the proper knurl and length you need for standard 1⁄2-inch lug nuts.
19. ear setups are a crap shoot: Some go easy with just one or two trial setups, and some can take a dozen or more before you get a good pattern. This one turned out to be the latter. Always start with the same shim thicknesses as the original gears and work from there. In this case, the original shims were really corroded and difficult to measure, and there was plenty of evidence that the last guy to put gears in the housing had no business being there. With the final piece of the puzzle in place, we buttoned everything up and prepared to wrestle our beefy new Dana 60 under the Jeep.