Speedy Auto > Car Tech > 4x4 > Transmission Drivetrain

Fullsize - Jp Magazine

Pete Trasborg Brand Manager, Jp

Have you ever had one of those projects that just seems to hit a wall at every corner? That’s how we feel about this axle swap. We’ve been working on it a long time, off and on, but we were shocked to see that we ran the first installment in Jp magazine over three years ago (“Fullwidth,” May ’09). We had always planned it as a multi-part story and we started off by making a case for swapping the stock Dana 60 front and Dana 70 rear axle under our ’68 M-715 for a more modern pair of 1-ton axles. In that first story we assembled a lot of the parts we were going to need and figured out how to get where we wanted to be. But there are always a lot of things to consider, especially when mixing and matching parts between the aftermarket and the junkyard.

fullsize 1968 M 715 On Jack Stands Photo 36360829

So it went: We’d figure something out, discover we’d need a new or different (usually $3) part, put in the order, and then one of the other Jeeps would break—or life would get in the way. And pretty soon we’d become aware that a lot of time had passed and our new axles were still taking up space in our garage. Rather than let more trial-and-error take up more time, we took the truck and axles down to Higher Ground 4x4 & Fabrication. Even if you don’t have an M-715, you’ll be able to take some good information away from these stories about what to consider when building and swapping junkyard axles into your Jeep. In this installment, we figure out how the new axles are going to go under the old Jeep and get them ready to bolt in. In the next installment, we’ll sling them under the Jeep and get it back on (and off) the road.

fullsize gear Sets And Bearings Photo 35032601

We went to Randy’s Ring and Pinion for all the front and rear axle innards we’d need. We told them that our Dana 60 front axle was from a ’93 F-350 and that the Dana 70 HD rear was from an ’87 Chevy C-35 to make sure we’d get the right parts. Those parts include 4.56 gears, master install kits (including front inner axle seals), front and rear hub bearings and seals, and even new Spicer 1410 U-bolt-style pinion yokes. PhotosView Slideshow

Jim Cox of Higher Ground 4x4 and Fabrication has been building axles and engines since he was 15. Once the front housing was gutted (especially including inner axle seals), he took a brush to clean any debris out of the axletubes. Once he was done scrubbing, he used compressed air to blow the tubes out and followed that with brake parts cleaner and a rag. This ensures that no residual grease or oil will catch fire or contaminate the new parts as the axle is put together.

We went with an Eaton ELocker for the front axle, but when Cox first dropped it in, it didn’t want to go. The carrier was hitting the casting of our pumpkin. A little clearance work with the die grinder removing just a little bit at a time was all it took. Cox ended up removing a swath just under 1⁄8-inch-deep by 1⁄2-inch-wide.

Once the carrier fit in the housing it was child’s play for Cox to get a decent pattern. We went with an ELocker because we drive this truck in all weather and leaving the locker off in the snow will help us maintain control. The instructions state that you should drill a 1⁄2-inch hole for the wires and rubber plug unless the area you are passing the wire through is thin, which surprisingly is the case of this area of the Dana 60. So, Cox drilled a 29⁄64-inch-diameter hole to ensure the plug won’t leak, per the instructions.

Once the gears were set up, Cox used an oxy-acetylene torch to blow the factory Ford brackets off the axle before finish grinding. If you are doing this at home, there is no reason that you can’t use an angle grinder with a 0.040-inch-thick cutting disc on it. The torch is faster, and on the Ford axle the sway bar mount on the driver side is between the centersection and the inner C and difficult to get a grinder into.

We used Mountain Off Road Enterprises’ 1⁄4-inch-thick, CNC-cut and formed leaf spring plates and shock mounts. We opted to leave the board-stiff factory 21⁄2-inch-wide leaf springs in the factory locations for now. Using the factory leaf spring spacing meant we needed to put the new perch on the casting. No big deal with the right experience and tools.

After the M.O.R.E. perch was ground out to fit on the 41⁄8-inch-diameter casting it was on to the next step. A lot of people are afraid of welding to cast iron, and rightly so. However, if you know what you are doing and have the correct equipment, it can be done safely and securely. The first step is to slowly pre-heat the area to be welded. Cox then welded on the perch with an arc welder and Ni-Rod 99 welding rod. The preheating prevents the casting from cracking and the Ni-Rod is intended specifically for welding to cast iron.

You are just asking for trouble having a 7,000-lb truck with a big-block V-8 turning 30-spline stub shafts. We upgraded ours using Yukon 4340 chromoly 35-spline parts and new Spicer U-joints with the factory inner short-side shaft. However, our eBay long-side inner shaft had the U-joint holes wallowed out, so we used a factory replacement from Yukon. Cox had to grind the Dynatrac knuckles and custom spacers so the larger-than-stock Yukon ears would slide into the axle. We also needed to get dust seals because our old stub shafts didn’t have any.

One of the big downsides to running the military HMMVW wheels is that the lockout hub tends to stick out and catch rocks and trees. With the dually hubs and the Dynatrac Dynalocs, the lockout is well protected from trail obstacles. The Dynaloc ring has an “O” to indicate free and an “X” to indicate locked; since we painted the ring we stamped an “X” into it with a cold chisel so that we’d know at a glance when we had the hubs engaged

The big problem with mixing and matching parts like this is that everything has to end up in the correct place. And there are a lot of places where it can go really wrong. From left to right, we’ve got the Ford dually hub (A), a new Ford replacement rotor from RockAuto (B), the factory Ford spindle (C), custom 1/2-inch thick adapter(D), Dynatrac outer knuckle (with ball joints, high-steer arm, and steering linkage) (E), Yukon outer stub shaft (F), and factory inner shaft (G). Cox puts a full ring of grease in the hub between the inner and outer bearing with a grease gun before installing the outer bearing and lockout hub.

One of the reasons to get rid of the rear axle is the oddball coarse-spline pinion and 1310 yoke. The 1310 yoke on the left measures 3.129 inches wide and the cap is 1.062 inches in diameter and is typically considered a 1⁄2-ton U-joint. The 1410 on the right has almost double the torque rating and measures 4.188 inches wide with a 1.188-inch-diameter cap. We had JE Reel modify our rear shaft so we could take advantage of the bigger yoke.

We normally sling the axle under the Jeep; loosely tighten the U-bolts, and then measure. Before doing anything, Cox likes to measure everything first and then do math to figure out where things need to go. He measures the pinion angle, spring center-to-center spacing, the angle of the spring where the axle sits at ride height, and caster (where applicable) of the original axles. Then he measures the new axles and marks them up where they need to get modified to match.

Some smaller and lighter Jeeps might experience handling quirks on-road with a Detroit Locker in the rear axle. With a wheelbase of 126 inches and a curb weight around 7,000 pounds, it is very unlikely we will ever feel anything coming from the back of our rig. By going with the basic Detroit Locker we keep things a bit simpler and saved some coin at the same time.

One of the big time-suckers on this project was the wheels. There are 8-bolt and 12-bolt HMMVW wheels. The military manual says to use the 8-bolt wheels for the bias-ply tires and the 12-bolt wheels for the radial tires. In practice, either will work for either tire type, but we wanted to go by the manual. If you are on the east coast you should have no problem sourcing wheels, but shipping them to the west coast is cost prohibitive. Fortunately, we found 100 Dollarman, who was local to us and had a pile of 12-bolt wheels. While our 37x12.50R16.5 Goodyear MTs were purchased directly from Goodyear, 100 Dollarman has good used examples for cheap.

While 100 Dollarman has the wheels at great prices, we still needed to get the hardware for them. Fortunately, shipping the small parts doesn’t break the bank. We first ran across JB Custom Fabrication while looking for a twin-stick shifter for another project, but the company has mil-spec hhttp://image.automotive.com/f/36360835/36360835.jpgardware for the HMMVW wheels as well. We were able to get new mil-spec valve stems, wheel nuts, and O-rings to assemble our wheels. We had the magnesium runflats, but they are too wide to work in the 12-bolt wheels, so we are running with no runflats.

Once all the welding and grinding was over, in true military tradition, we spray-bombed everything in OD green. We went to Army Jeep parts for some Gillespie Coatings paint. We used #24052 USMC Semi-Gloss green over Red Oxide III Zinc Rich primer to cover everything.

Body Chassis Transmission Drivetrain Electrical Engine Suspension Brakes Wheels Tires Tech QA

Fullsize - Jp Magazine

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