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Techline: Your Top 4x4 And Off-Road Tech Questions Answered Here

Posted in How To: Tech Qa on April 27, 2017
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Surplus Tire Trauma

I am building my own version of your Bug-Out Blazer, although mine is a ’87 Ramcharger. It has a mechanically injected 12-valve Cummins in front of a manually shifted 46RH transmission, which drives an NP205 transfer case. The axles are spun with 1410-series driveshafts and consist of a Dana 60 up front and a 14-bolt rearend, both running 4.10:1 ratio gears and Grizzly lockers.

The suspension is just a simple 4-inch Skyjacker kit with new leaf springs all around. The truck is running 35-inch tires right now, but my plan is to bump up a little to 37s. I've decided to use the 37x12.50x16.5 military take-off tires on recentered double-beadlock Hummer wheels.

Now for my question: Is the military Goodyear Durawall MT/R or the military BFGoodrich Baja T/A a better tire and why? When the truck isn't being used to escape the zombie apocalypse, it’ll be our backcountry camping rig, seeing everything from dry asphalt to moderate trails. Snow, mud, gravel, dirt, and sand are all likely to be encountered at some point. I don't really care about tread noise or harshness (12-valve Cummins, remember), but carcass strength and treadwear are a factor. Any thoughts?

Name Withheld
Via email

Military surplus tires are a great way to save a little bit of money on rolling stock. It’s not uncommon to find surplus tires that have better than 80 percent of their tread left. The downside is that the surplus 37x12.50 HMMWV tires are only available for 16.5-inch wheels. These wheels do not have a safety bead to keep the tire in place at lower air pressures off-road. However, you will have that problem solved by using the double-beadlock wheels. It’s an extremely heavy tire and wheel combo, which will affect overall suspension, brake, and driving performance, but the combo can be found for hundreds of dollars cheaper than comparable 37-inch tires and wheels.

There were several different military HMMWV tires used over the years. The best tires are the latest versions, which include the Goodyear (goodyear.com) and BFGoodrich (bfgoodrichtires.com) tires you are considering. Companies such as 100 Dollar Man (100dollarman.com), Boyce Equipment (boyceequipment.com), Gov Planet (govplanet.com), and Government Liquidation (govliquidation.com) offer military surplus tires and wheels.

The thing to remember is both the Goodyear and BFG military tires are designed to be survivability tires, similar to the BFG Baja T/A used for desert racing, which is one of the reasons they are so heavy. They are 8- and 10-ply D and E rated tires designed to carry a lot of weight and not come apart if they need to be driven on while flat for several miles. As I’m sure you can imagine, you can’t just get out and leisurely change a tire while bullets are whizzing through the air in a combat environment. This extra durability built into the tires makes them great for enthusiasts that frequent areas with especially sharp rocky terrain, hidden stumps in the mud, and other obstacles that tear up tires. Unfortunately, this extra durability also makes them less compliant on- and off-road, which leads to a rougher ride and decreased traction when compared to traditional radial mud-terrain tires. Stiff heavy-duty tires are not able to conform around and envelope off-road obstacles as well, especially on a lightweight vehicle. Granted, your Ramcharger with a Cummins powerplant isn’t exactly light, but it is still nowhere near the weight of an uparmored and fully loaded HMMWV.

I think both the military surplus Goodyear and BFG tires will perform well enough for what you have planned. Of course, BFG offers data that says its military tire will provide a 22.5 percent increase in projected tread life, has 11 percent more wet pavement maneuverability and 8 percent more dry pavement maneuverability during evasive maneuvers, and 20 percent better mud traction. Although, I think the tread pattern of the newest surplus Goodyear tire will perform slightly better than the BFG version if you encounter snow and ice.

14-Bolt Discs

I have a quick question about 14-bolt disc brake conversions. I have a ’92 Chevy 3/4-ton Suburban 4x4. I want to put disc brakes on the rear, but a quick search for bolt-on kits shows that, for the most part, kits aren’t available for my year/axle type. My Suburban has the drums that slip on over the studs from the face of the hub/axle flange, not the drums that mount on the back of the axle flange and are held in place by the pressed-in wheel studs. I would also like to keep an emergency brake. I don’t understand what the big deal is and why most companies don’t offer kits.

I’m assuming I could find factory parts in a junkyard and was wondering what year did GM start offering factory rear disc brakes on 14-bolt axles?

Also, none of the kits I saw mentioned anything about master cylinder or proportioning valve changes. Although, the original setup may work with disc brakes. I can’t help but think that, ideally, changes should be made when switching from drums to discs. Any thoughts?

Al Miccio
Via email

The GM 14-bolt axle has gone through a few changes throughout the years. The brakes and flanges are among those changes. It’s important to make sure you get the right kit for your 14-bolt when switching to disc brakes. As you have found, the ’86-and-up slip-over drum brakes require a different disc brake kit than the stud-mounted drums. Fortunately, TSM Manufacturing (tsmmfg.com) offers a disc brake kit for your application. It includes an emergency brake. The company also has the instructions up online so you can see what the process is prior to purchase and installation. TSM Manufacturing claims that the disc brake kit works perfectly with your factory ABS system. If you do not have ABS, an adjustable proportioning valve is available for the rear brake line if you are experiencing abnormal rear wheel lockup.

Hub Envy

I have a ’06 Ford F-150 4x4. Over the last 48 years, on every 4x4 that I’ve owned except my first, a ’48 CJ-2A, I was able to install a traction-aiding device (Truetrac) and Warn manual locking hubs up front. It seems nothing is available for any of the 1/2-ton pickups, and anything that is out there isn’t recommended as it would likely lead to parts failure. The IFS is to blame I’m told.

What is the most cost effective way to get a little more traction up front on my F-150 and have locking hubs too?

Jack Segovich
Via email

As you have found, the traction-adding differential options are very limited and sometimes nonexistent for most factory IFS 4x4 frontends. The reasons are many. IFS axlehousings are generally made from aluminum and can’t take the same punishment that the old iron and steel solid front axles can take. Also, many of the newer trucks have less robust steering gear systems or rack-and-pinion steering, neither of which lends itself to the increased torque applied to them when a traction-adding differential is installed in the front axle. Lastly, it’s just not that common of a request, so few parts exist to do it. The good news is that there are plenty of traction-adding differentials available for the rear of your Ford F-150. A rear traction-adding device will generally make a bigger difference in trail performance than a front one alone in most cases. The rear axle in your F-150, and most 4x4s, is much stronger than the frontend, so it can handle the extra traction and torque load that the traction-adding device will apply.

As for manual locking hubs, there is no easy or affordable way to install them on a ’04-’14 Ford F-150. Ultimately, there really isn’t a need for them. The ’04-’14 F-150 has actuators in the knuckles that engage and disengage the axleshafts via vacuum. They essentially serve the same purpose as a manual locking hub by disengaging the axleshafts from the wheels and tires. So in a sense, you already have locking hubs, it’s just a different design than what you are used to and they operate automatically when you engage four-wheel drive.

Rubi Calibration

I just read your article about regearing on fourwheeler.com. If my calculations are right, I need 4.56:1 ratio gears in place of the factory 4.10:1 ratio gears in my ’06 Jeep Rubicon Wrangler. I have installed 33-inch tires. Does the automatic transmission come into play? I have a Superchips tuner, but on the pre-’07 Wranglers I cannot program the Jeep for bigger tires. The Jeep is stock except for the lift and tires.

Scott Requa
Via facebook.com/fourwheelermag

The absolute best performance modification you can make to your 4x4 is to match the axle gears to the tire size. The gears give the engine the leverage it needs to compensate for the larger aftermarket tires. Selecting the correct ratio for your application isn’t always as easy as making a few calculations or referencing a chart. You have to take many other things into consideration including driving habits. If your 4x4 sees a lot of high-speed cross-country freeway trips, you’ll likely want a less aggressive gearing upgrade than someone that tows their 4x4 to the trailhead and only drives it around town. Areas with mountain ranges and steep grades can be more easily traversed with deeper gearing too. Quite often a specific tire size will fall in between two available gear ratios. These other driving elements need to be considered when choosing if you should go with the higher or lower gears.

The first thing you should do to a modern lifted 4x4 is correct the speedometer. Having an accurate speedometer reading is only a very small part of the reason for doing this. The more important reason is to help the transmission and engine work better together and live longer. Both the transmission and engine computers rely on a correct speedometer reading. The vehicle speed is used to help adjust ignition timing, fuel input, transmission line pressure, shift points, and more. In extreme cases, an incorrect electronic speedometer reading could cause the check engine light to trigger or cause transmission failure.

The ’03-’06 TJ Wrangler Rubicon has the NV241OR transfer case. This transfer case features an electronic speedometer sensor and tone ring. Most other TJ Wrangler models feature a mechanical speedometer gear, so correcting the speedometer is only a matter of installing a new small plastic gear that runs $30-$40. Unfortunately, your speedometer requires electronic calibration. Some people have had good luck taking their Jeeps to the dealer to have the speedometer reflashed. Other people claim that their speedometer is still not accurate after the dealer reprogramming. However, you have another option. Blue Monkey Motorsports (bluemonkeymotorsports.com) offers the SpeedoHealer for the ’98-’06 Jeep Wrangler TJ, ’04-’06 LJ Wrangler Unlimited, and ’98-’01 Cherokee XJ. The SpeedoHealer is a plug-and-play speedometer programmer that features factory OEM connectors for water resistance. It gives you the ability to set up your Jeep for any tire diameter and axle gear ratio combination.

The 4.0L inline-six in your Jeep makes a ridiculous amount of low-end torque. It’s a great engine for off-roading, and the low-end torque makes it incredibly tolerant of oversized tires with stock axle gears. In your case, there probably isn’t a real need to go from a 4.10:1 ratio gear to a 4.56:1 ratio gear. The change is very small. And while you would notice a performance increase, most of us would not be able to justify the cost for such a change. I would recommend sticking with the stock 4.10:1 ratio axle gears and correcting the speedometer. If you decide to step into 35-inch or bigger tires down the road, then you should start looking at a ring-and-pinion gear swap too.

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