Overland Vehicle Outfitters

Project Flatfender: Front Axle

Front Axle
In the spirit of full disclosure:  I actually had two later model narrow track D30 axles in my barn when I started the project.  One had spring-over axle pads welded to the top of the tubes, so I selected the other to avoid working around them or cutting them off.  After spending a large number of hours cleaning, prepping, replacing bearings and seals, and getting the ring and pinion gears set up just right (with a beautiful pattern, I might add!), I went to insert the driver's side axle only to find that the long-side tube was bent just enough to cause fitment issues.  Needless to say, I was a little perturbed with myself for not verifying early on that the tubes were straight.  I'm still kicking myself when I think about the extra effort it took to build the second axle.  The moral of this story?  Learn from my mistake and check your axle tubes before you start to rebuild it!     
 
With the plan to swap in a later model open-knuckle Dana 30 front axle, I decided to start with cleaning, prepping and rebuilding the "new" front axle. The axle housing was in good shape overall, as were the axle shafts and differential carrier. The ring and pinion gears had quite a bit of wear and two small chips in the teeth. (Rather than try to reuse them and hope for the best, I'll invest in a new ring and pinion set.) It was extremely dirty inside the pumpkin and there was quite a bit of crud in the axle tubes. I powerwashed the outside of the housing, then removed all the components and hosed down the inside with brake cleaner. I also removed the steering knuckles and began soaking the ball joints in PB Blaster penetrant. Below you'll find a picture of the Dana 30 axle housing after being powerwashed, followed by pictures of the cleaned and painted axle housing.

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The upper and lower ball joints were removed from each of the steering knuckles and, once separated, I cleaned and painted the knuckles as well.  I selected quality TRW replacement ball joints that should last for many thousand miles, even under hard off-road use, and will ensure tight handling and extended tread life for those expensive tires.

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It's important to note that on a Dana 30 from this era, the upper ball joints require a threaded insert that acts as a sleeve to seat the ball joint at the appropriate depth.  Be careful not to damage this insert as you'll reuse it.  It's possible to remove the insert with a large, flat object (in the picture I'm using a large chisel), but for reassembly you'll need the specific wrench (pictured below) to get it right without damage.  The wrench is fairly cheap, can be found at your local auto parts store, and is well worth the price to ensure your ball joints are installed properly. 

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I've had quite a bit of experience with axle u-joints, but on a vehicle this old I still have a healthy amount of dread for servicing them.  I know there are some grizzled old veterans who can replace a set with nothing more than a hammer, a flat surface, and 15 minutes without breaking a sweat, but I haven't mastered that art yet.  These original shafts were particularly fond of the u-joints and stubbornly refused to give them up.  I hosed them down with PB Blaster and let them sit overnight before even attempting removal.  Since my usual socket and vice approach wasn't working, I broke out the u-joint/ball joint press and the impact wrench.  After much sweat, a little blood, and a significant amount of swearing I finally got the old joints removed and the new Spicer joints installed.  The primary aspect of this job that contributes to the difficulty is ensuring that you don't damage the yokes on the axle ends while you're applying a great amount of force.  Once you've got the new joints installed, a minimal amount of binding is normal.  A few well placed raps with a hammer around the base of the ears is usually all it takes to loosen them up throughout the range of movement. Below are pictures of the removal process and the shafts with new joints installed.

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Another item I chose to address was the OEM axle vent. The older style, as found on both the front Dana 30 and rear Dana 44 on this vehicle, was a hole in the top of the differential housing with a check valve installed. As the vehicle is driven and the gears heat up the oil in the differential, pressure builds and needs to be released. The check valve allows the pressure to be released as necessary, but also keeps water and debris from entering the differential. This is a fairly effective system, but during deep water crossings when the diff is submerged, water can be sucked in through the check valve. Most late model vehicles use the same method (check valve) for venting but mount it remotely on a rubber hose well above the differential. This isn't a foolproof method, but it definitely adds an extra measure of protection for your diff.

I removed the OEM check valve from the diff housing, then used a tap to cut the correct thread type in the hole that matched a threaded, barbed hose fitting. I used Teflon tape on the fitting's threads and a right-sized O-ring for a positive seal. Now I can attach a section of rubber hose, route it up high on the body, and cap it with a check valve. 
 
Below right is a picture of two OEM differential covers; the one on the left was installed on this particular axle and is made of thin metal that could be easily dented or punctured in the rocks.  The one on the right is also an OEM Dana 30 diff cover, but it's the much heavier design that is a full 1/8" thick.  Installing this cover will provide much improved protection for the front axle gears.  

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My choice of traction aid for the front Dana 30 was the proven Eaton Detroit Truetrac.  The Truetrac is unique in its approach to limiting wheel slip, and subsequent traction loss, in that it employs helical gears rather than the more common multi-clutch packs that wear over time and eventually require replacement.  As a result, the Truetrac has no "wearable" parts and requires no special maintenance.  It is automatic, performing as an open differential until one wheel looses traction, at which time the pinion- and side-gear separation forces seamlessly transfer torque to the wheel with the most traction.  The Truetrac will progressively (smoothly) transfer torque as needed but, being a limited-slip rather than a full locking differential, it will not provide 100% lockup.  These characteristics make it ideal for front axle applications. 
 
My rationale for choosing the Truetrac?  Automatic full locking differentials are not recommended for the front axle of street-driven vehicles, especially short wheelbase vehicles driven on the street in snow and ice.  This leaves limited-slips and selectable lockers as the two choices.  I prefer the assurance of an automatic traction aid that doesn't require manual intervention.  And a selectable full-on front locker is still going to fight against steering inputs and cause squirrelly handling when engaged.  With the type of four-wheeling I do, situations where I need a full locker up front are rare.  Throw in the proven durability, lack of need for special maintenance, and reasonable price of the Truetrac, and it's the ideal choice for my Jeep. 
 
(Sidebar:  I have used several different styles of automatic and selectable lockers in various Jeeps that I've owned, including an Eaton Detroit Locker in an '86 CJ-7, an ARB Air Locker in an '83 CJ-5, the OEM front and rear TruLok lockers in an '03 Rubicon, and the OEM Vari-Lok gerotor-based system in an '02 Grand Cherokee WJ with Quadra-Drive.  I'm a big proponent of traction aiding differentials, and all of the above have their strengths in the right application and usage.  For instance, the Detroit Locker is bulletproof, offering 100% lockup in a self-contained, simple unit that requires no driver input.  It's always ready when you need it, and it foregoes the complexity of running additional wiring, onboard air, or cables.  The downside is the noise and harshness of the differential locking/unlocking while cornering on the street, which can be jarring if you spend much time on the pavement.  It can also be downright scary on snow and ice on pavement, as the locked rearend attempting to push the vehicle forward can drive you right for the low side of the road.  To say nothing of the embarrassment of being passed by front-wheel drive Hondas as you struggle to make it up a mild icy hill in a built Jeep!  If you live in a year round warm climate, however, this is a non-issue.  For me, my favorite arrangement was the OEM Rubicon locker setup.  You have selectable front and rear lockers, and when disengaged, the rear contains a helical gear-driven limited-slip that is perfect for mild four-wheeling or the icy/snowy conditions I just mentioned.  However, the downside there is the complexity of the electric and air-actuated components.  My point being that the most important consideration when choosing a traction aiding differential is the conditions you drive in, the off-road situations you plan to tackle, and the overall intended use of your 4x4.  Complexity and maintenance requirements are also important.  If you do your homework, you'll find the traction aiding differential that best suits you and your vehicle.) 
 
Below are pictures of the Truetrac, along with the original open carrier with ring and pinion gears for comparison. 

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I've set up quite a number of ring and pinion gears over the years, but there is one resource I always have on the workbench with me: a printed copy of the PDF article "Gettin' the Gears Done" by Bill "BillaVista" Ansell.  You can find the online version at the Pirate4x4 site, where there is also a link to download the PDF.  This is still the best work aid and instruction manual for gear setup that I've ever come across, bar none!  The information provided for context, along with the detailed pictures and step-by-step instructions is outstanding - I highly recommend saving a copy for your garage. 
 
When disassembling the differential ring and pinion, take the time to mark which side the differential shim packs came from.  I like to tie them together so they don't get separated.  This is also recommended for any pinion shims, baffles, and oil slingers.  It's important to be able to reference what came out of the diff when you begin reassembly.  If you're this deep into axle work, it's always a good idea to replace any seals that are questionable, so after dismantling the hubs, rotors, and removing the axle shafts, I removed the inner axle seals.  For this I simply use a long section of pipe or a wooden dowel inserted through the outer edge of the axle tube, and give a few good raps with a hammer; this is usually enough to unseat the seals.  For installing the new seals, I use the same approach but from the other direction, and I use a socket that is sized to match the steel section of the seal.  This is best done with two people, and care must be taken not to damage the rubber portion of the seal. 
 
Removing the pressed bearing on the pinion can be accomplished with a bearing separator and a press.  My press is a 12-ton unit from Harbor Freight.  For the differential carrier bearings, however, the press won't work due to lack of carrier clearance.  In my younger days, I have carefully used a cut-off wheel and a chisel to cut through the bearings and remove them, but this is not the ideal method as you run an increased risk of damage to the carrier itself.  I now use a Posi-Lok 3-jaw gear and bearing puller.  It's one of those tools that is an investment ($100-plus on eBay), but it will pay for itself the first time you have to use it.  Since the Truetrac replaced the stock carrier, it wasn't necessary to remove the old bearings from the carrier other than to retrieve the shims.
 
While setting up the gears, it will be necessary to remove/install the carrier bearings multiple times as you adjust shims.  You don't want to do this with the new bearings, as you run the risk of damaging them, and it's way too much work.  Use the old set of bearings that you removed to make a set of "setup" bearings that you can use on any Jeep D30.  Using a Dremel-style tool and a grinding wheel, uniformly grind the inner diameter of the bearing (checking it often for fitment) until it will just slip fit onto the carrier.  It will be snug, but it should be only finger tight and easily removed.  Once it's ground to the right ID, give it a quick rinse with a solvent to remove any metal particles, and then oil it lightly once dry.  This will make your gear setup much easier.  This same method can be used to make "setup" bearings for the D44 rear as well.
 
Below are pictures of the marked bearing caps, the final gear pattern after setup, the Lube-Locker diff cover seal, and the Dana 30 Master Rebuild Kit which includes everything you need to rebuild your differential or install new ring and pinion gears.     

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It's important to note that the carrier bearing caps must also be marked "L" for left and "R" for right, or to remove any doubt, "D" for driver and "P" for passenger.  These must be reinstalled in the same position and orientation.  For the differential cover seal, I chose a Lube-Locker, which is a heavy-duty reusable seal that doesn't require any RTV or other sealant - it installs dry.  Gone are the days of using messy silicone or disposable gaskets that must be scraped off each time the cover is removed. 

An additional note on gear setup:  one of the practices recommended by Bill Ansell (as referenced above) that I've found to be essential is to record the measurements for each of the four key settings (pinion depth, pinion bearing pre-load, carrier bearing pre-load, and backlash) during each gear setup "attempt" or iteration.  The entire gear setup process essentially involves adjusting these four interconnected settings until all are within spec, so you will have multiple iterations of setup, measurement, and adjustment.  It's critical that you record these measurements for reference.  I also include my observations with each attempt, i.e. "contact pattern is too close to the ring gear root", which helps me remember why I made the adjustments that I did.  The first couple of times I set up gears I didn't record any measurements, and by about the third iteration I was asking myself "Wait, did I try that before?  Wasn't that my shim pack measurement the first time?"  Needless to say, my results were less than stellar and I got the opportunity to do it all over again with new parts.  Feel free to learn from my mistakes and follow this practice the first time.  You're welcome! 

Ring and pinion gear setup can be one of the most daunting automotive tasks, but also one of the most rewarding.  When you see that final contact pattern with the markings spot on and all the settings within specification, it makes all the time and effort worth it.         

E-mail us at:  rmiller@ovoonline.com

Overland Vehicle Outfitters
Marysville, OH 43040