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Your Top 4x4 and Off-Road Tech Questions Answered Here

Posted in How To: Tech Qa on January 25, 2017
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35-Spline Standoff

I’m building an early Bronco. It will have a built 302ci V-8, ZF-5 manual transmission and an Advance Adapters Atlas four-speed transfer case. It will be rolling on 37-inch tires with ’04 Ford Super Duty axles. Would you go to chromoly axleshafts and 35-spline outer stub axles on the front? Or would you keep the stock front axleshafts and 30-spline stub axles so replacement parts will be easier to find? I’m not sure if I need the extra strength or not.

@iamtaylorcorbett
Via Instagram @cappaworks

It sounds like you are backing up the healthy V-8 and 37-inch tires with some heavy-duty components. The strength of the axleshafts you need will really depend on how you drive it. If you only plan to run down the dirt road to grandma’s house, the 30-spline stub axles will hold up just fine. But the reality is that with the drivetrain combo you have planned, I suspect you will be really using this Bronco off-road. The compounded low range of the Atlas four-speed transfer case coupled to the direct drive and low First gear of the manual transmission could cause axleshaft problems. This is especially true if the tires were to become wedged in an undercut or you hop and bounce the Bronco up a ledge.

Your ’04 Ford Super Duty axles are likely the venerable Dana 60 frontend and the Sterling 10.75-inch rearend. The Super Duty Dana 60 front axle will have 1.50-inch-diameter 35 spline inner axleshafts and smallish 1.31-inch-diameter 30-spline outer stub axleshafts. These outer axleshafts are the same exact size and spline count as what you can find on a Dana 44 inner axleshaft. This isn’t very reassuring in my mind, but let’s look at some numbers.

A stock 1.31-inch-diameter 30-spline Dana axleshaft is said to have an ultimate break strength of about 6,000 lb-ft. A stock, 1.50-inch-diameter 35-spline Dana axleshaft is said to have an ultimate break strength of about 9,000 lb-ft. This means that a stock 35-spline stub shaft would be 50 percent stronger than a 30-spline stub. That’s a pretty significant difference, and we haven’t even considered going with chromoly axleshafts yet.

A high-quality aftermarket 1.31-inch-diameter 30-spline 4340 chromoly axleshaft is said to have an ultimate break strength of about 10,000 lb-ft. While a high-quality aftermarket 1.50-inch-diameter 35-spline axleshaft is said to have an ultimate break strength of about 15,000 lb-ft. Of course, these numbers vary depending on the quality and the manufacturer. It’s important to remember that not all axleshafts are created equal.

If you’ve decided to upgrade to 35-spline stub axles, you’ll also need to upgrade to aftermarket 35-spline unit bearings. Companies such as Currie Enterprises (currieenterprises.com) offer 35-spline unit bearings, while Currie and Spidertrax (spidertrax.com) offer heavy-duty 35-spline unit bearings in several popular lug patterns with larger wheel studs.

The other option is to simply install the complete Dynatrac (dynatrac.com) 35-spline Free-Spin kit. The Dynatrac Free-Spin heavy-duty hub conversion kit replaces the factory unit bearings and 30-spline stubs with fixed spindles, serviceable wheel bearings, and 35-spline stub axles. Free-Spin kits are available with 35-spline Dynatrac DynaLoc manual locking hubs, which are said to be three times stronger than other 35-spline manual locking hubs and offer a shorter profile for more clearance on the trail.

Now, if you wanted ultimate in overall axleshaft strength combined with ultimate steering joint strength, you should head into some RCV (rcvperformance.com) CV-style axles. These 35-spline inner and outer axles are warrantied for life with up to 47-inch tires. However, you’ll still need to switch over to 35-spline unit bearings for these axleshafts to fit your Dana 60.

Highboy Power Steer

I own a ’73 Ford F-250 Highboy 4x4. It has a Dana 44 frontend. I’m not sure if you have much experience with the old Fords, but what is needed to convert it to power steering from the old “armstrong” steering?

@ultimateteamroper
Via Instagram @cappaworks

Most ’70s F-250s either came with manual steering or a really oddball complex and problematic factory Bendix power ram-assist steering system. Unfortunately, the original Bendix ram-assist is just about as desirable as the manual steering. The Bendix system is also getting hard to find parts for. The good news is that Benchwork Steering Systems (benchworksteering.com) offers a power steering conversion kit for the ’66-’77 Ford F-250 Highboy 4x4 3/4-ton trucks. Each kit includes a rebuilt 16:1 ratio Ford power steering gear box, an intermediate shaft, a pitman arm, a draglink, a bolt-on bracket to mount steering gear to the frame, factory-style hoses, and all the required hardware. An optional 14:1 fast steering box is optional. You’ll also need to add a power steering pump to your engine. If you can’t locate a pump and bracket locally, Benchwork Steering Systems offers a kit with a rebuilt pump.

JK Lift Specific

I’ve been looking at 4-inch lift kits for my ’09 two-door Jeep Wrangler. I like the looks of the Skyjacker kit, but is there another comparable lift kit with more bang for the buck?

@lamarstowe
Via Instagram @cappaworks

As you have probably noticed, the pricing of comparable Jeep Wrangler JK lift kits is very competitive. What you may not know is that the least expensive kit is not always the best lift kit for your application. If you don’t plan to load your Jeep down with a lot gear most of the time, you’ll want to steer into a lightly sprung lift kit like one of the Skyjacker (skyjacker.com) Softride lift kits. The Softride lift is available with several different shock options. Choose the shock that best meets the on- and off-road driving demands you have planned. For general on- and off-road use, a standard twin-tube shock will work fine. For more high-speed two-track use, consider going with the Skyjacker M95 monotube shock absorber. These will dissipate heat better than traditional twin-tube off-road shocks.

Center Diff Difference

What is a central locking differential and why do those limey European rigs have them and our American ones don't? What gives? What’s the benefit between their system compared to our standard 4WD transfer case?

@aguijimenez
Via Instagram @cappaworks

The center locking differential isn’t just a component found on overseas 4x4s. It can be found on any 4x4 with both full-time and part-time 4x4 transfer case settings. This includes some current model Jeep Grand Cherokees, the ’17 Ford Raptor, and some GM trucks, among others.

A central locking differential is located in the transfer case and performs a function similar to the differentials found in traditional axles. The full-time four-wheel-drive setting is designed for use on the street where very little tire slip occurs. When the vehicle is in full-time four-wheel drive, there needs to be some differentiation between the front and rear axles. The front end of a vehicle will take a corner much wider than the rear end, therefore the front end travels a further distance than the rear end. That difference needs to be compensated for, and that’s exactly where a center locking differential comes into play.

Now, when you are ready to hit the dirt, you shift the transfer case into part-time 4x4. This locks the center differential and makes the 4x4 more off-road worthy. The front and rear tires are able to slip on the loose or slick off-road surface to compensate for the difference in distance traveled by the front and rear axles.

C-Clip Confused

I see all these ads for heavy-duty aftermarket axles from Currie, Dynatrac, and others, but they are C-clip axles. Aren’t C-clip axles weak compared to full-float axles? Why spend a ton of money and build up a custom axle assembly with C-clip axleshafts? Are there aftermarket heavy-duty C-clips? Or are C-clip axles a lot harder to break than everyone makes it seem?

Gabe P.
Via email

You may be a little confused about the different axle types. There are three common axleshaft designs found on 4x4 axle assemblies. These include the C-clip, semi-floating, and full-floating axleshaft designs. C-clip-style axles usually have the axle bearings and seals pressed into the axlehousing ends. The axleshafts feature a slot machined at the end and are slid into the housing. They are retained in the housing with small C-shaped clips, which are inserted through a window in the differential carrier. When a C-clip–style axleshaft fails, it can freely slide out of the axlehousing, which as you have noted is not at all ideal. The vehicle becomes undrivable. C-clip axles are generally best suited for stock low-horsepower and low-load applications. Larger than stock tires, increased horsepower, and abusive off-road driving are a bad combination for C-clip axleshafts.

A semi-floating axleshaft looks similar to a C-clip-style axleshaft, except the axle bearing and seal are pressed onto the axleshaft and bolted to the axlehousing end with a retainer plate. If a semi-floating axleshaft fails, the wheel end remains on the axlehousing in all but the most extreme failures, however the vehicle is usually undrivable. Semi-floating axleshafts are the most common rear axle design found on aftermarket axle assemblies offered by companies like Currie Enterprises (currieenterprises.com) and Dynatrac (dynatrac.com). I believe you have confused semi-floating axleshafts with C-clip axleshafts.

Full-floating axle assemblies are generally reserved for high load capacity applications, such as the rear axles found in 3/4- and 1-ton trucks. Full-floating axles have bearing spindles either bolted or welded to the housing ends. These spindles and wheel bearings support the weight of the vehicle and payload. The axleshafts slide in through the hollowed spindles and either bolt to or spline into the wheel hub. The axleshafts do not carry any of the vehicle weight, they only transmit power from the differential to the wheels. If a full-floating axleshaft fails, the wheel end is unaffected and the vehicle can continue on in four-wheel drive or in two-wheel drive on the remaining axleshaft if the axle has a locking differential.

Autotrac Attack

I would like to start off by saying you guys put out an amazing magazine that I have learned a lot from. I have had a subscription since I was 10. It’s been 20 years! I’m having an issue with my daily driver/camping/off-road rig that I’m hoping you can help with. I have a ’06 Chevy 1500HD with a tuned 6.0L. The truck has a 4L80E automatic transmission and an Autotrac transfer case. I have installed a 7-inch BDS high-clearance lift kit and 35-inch Mickey Thompson Baja Claw tires, a rear Detroit Locker, a Kryptonite steering kit, 1410/1350 driveshafts, a Warn M12000 winch in an ARB bumper, a TrailReady rear bumper, and a bunch of other stuff.

The issue I’m having is with the Autotrac transfer case. It keeps going through clutches. When they go, I’m down to two-wheel drive. The transfer case has been rebuilt at the GM dealership three times and once it was replaced with a brand new GM unit. None of them have lasted very long. I don’t ever use the auto 4WD feature to save on clutch wear, but it doesn't seem to matter. I am looking at swapping to a transfer case with no clutches, or at least a transfer case that locks in gear. I have done driveline swaps on older trucks, but I’m unsure on how to deal with the ABS or any other computer issues. What transfer case would be the best bang for my buck? I am fine with cutting a hole in the floor to run shifters. I drive the truck pretty hard on muddy trails, as well as long rough roads at higher speeds. Being in northern Canada with six months of winter, I’m in four-wheel drive fairly regularly, even on the highways. The truck also performs pulling duties. It sees a mix of all types of driving and conditions, many out of cell service so it has to remain reliable.

Also, along those lines do you know of a hub/wheel bearing upgrade kit as well? Thank you in advance for the advice and it would be an honor to meet you guys on the trail someday!

Daniel Wythe
Via email

The NV246 Autotrac full-time four-wheel-drive transfer case in your truck has some admirable features. Although, they are more useful in a stock truck. As you have found, the NV246 has questionable durability when coupled with more power, bigger tires, and regular off-road use. It’s a perfect candidate for a swap, especially in your application. I think the best bang for your buck would come from an NV241 part-time transfer case with a manual shifter. You might also consider the push-button NV243 part-time transfer case. These swaps are not totally insurmountable. The ABS will be unaffected, but you will need to splice your trucks wiring harness into the VSS sensor on the new transfer case. You’ll also likely need to modify the normal things like the transfer case shift linkage/wiring, driveshafts, and so on. The NV241 and NV243 are very heavy-duty transfer cases that should have no problem putting up with what you and your truck dish out.

As for the wheel bearings, there really isn’t a lot you can do aside from having expensive one-off custom-fabricated uprights made with traditional serviceable spindles and wheel bearings. The other option, which interestingly enough might cost about the same, would be to swap in a solid front axle.

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