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

Posted in How To: Tech Qa on February 28, 2019
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Solid-Axle Yukon

I have a ’95 GMC Yukon. I have been searching for around a year now trying to find out if there is a solid front axle that would fit the current driveline under my Yukon without having to do a complete transmission and transfer case swap. I totally understand the whole frontend is going to need some modifications done, but the transfer case I have, and the transmission has already been rebuilt. I would just hate to have to switch out for an off-the-shelf transmission and transfer case. Thank you for any help.
Name Withheld
Via facebook.com/fourwheelermag

The ’92-’99 GMC Yukon SUVs enjoy a vast abundance of aftermarket parts availability. There are plenty of lift kits that work with the IFS front suspension. However, like many others before you, you’ve probably found out that the IFS suspension, axle, and steering assemblies don’t hold up well to the installation of larger tires and abusive off-road use. A solid-axle swap is a sound decision. The front axle you choose will depend on the solid-axle swap kit you use to make the conversion. Offroad Design (offroaddesign.com) offers several bolt-on solid-axle conversion kits for your Yukon that give you a selection of front axle and leaf-spring options. The axle options include the use of either a ’70s Ford solid front axle or an ’85-’97 Ford Dana 60. The ’85-’97 Ford Dana 60 will likely be much easier to locate at a wrecking yard or in the local classifieds than the ’70s Ford front axle. Keep in mind that the Offroad Design kits have 3 inches of lift built into them when choosing your leaf springs. The kits also move the front axle forward an inch for more fender and cab clearance around the tires. Off Road Unlimited (offroadunlimited.com) also offers solid-axle swap kits for your Yukon and other Chevy and GMC trucks and SUVs.

If your Yukon came with the NP246 Autotrac transfer case, you’ll have to swap it for an NP241 or NP243. The NP246 will not work correctly without the factory front axle sensors found on the original IFS assembly. Yukons equipped with the NP246 Autotrac transfer case will have push-button switches on the dash with an auto-4WD option. Offroad Design offers several NP241/NP243 input gears that can be used to help simplify your transfer case swap, which you may or may not need depending on what versions of these transfer cases you can get your hands on.

2WD Low Toy

I have a ’01 Toyota 4Runner that I love. It wheels and drives great. Is there any way to add a 2WD low gear to the transfer case? I know some of the Jeep and Chevy vehicles have available aftermarket 2WD low boxes. Is there something similar for my ’01 SR5 4Runner?
@eric_mcgrew
Via Instagram @cappaworks

A low-range two-wheel-drive option can be very handy when parking a trailer or maneuvering through tight areas that don’t require four-wheel drive. In paved areas, the use of four-wheel drive low range will reduce maneuverability and cause excessive driveline bind, so we can appreciate the desire to add a 2-Lo feature. There are a couple of ways to go about this, and the method works for you will depend on the application. We’ll go ahead and cover the two-wheel-drive low possibilities for more than just your particular Toyota.

If a Toyota or other 4x4 has front manual-locking hubs, you can simply unlock the front hubs and shift the transfer case into low range as you normally would. The front driveshaft, ring-and-pinion, differential, and axleshafts will spin, but power will not be transmitted to the front wheels. None of these components will be damaged by spinning under no load. However, you’ll need to drive sanely to avoid overloading the rear differential. On most vehicles, you’ll be nearly tripling the torque sent to the rear axle.

If your Toyota has the Automatic Disconnecting Differential (ADD) axle-disconnect system, there are no locking hubs and the front axle is disconnected when the transfer case is shifted into two-wheel drive. When the front axle is disconnected, both outer axleshafts, one inner axleshaft, and the differential gears spin, but the front driveshaft does not. Shifting the transfer case into 4-Hi or 4-Lo energizes the ADD on the front axle assembly, engaging the disconnected front axleshaft. You can trick the system by tapping into the wiring harness and installing a switch, which can be used to independently control the ADD axle engagement regardless of transfer case shifter position. This will give you the ability to shift the transfer case into 4-Lo without supplying power to the front tires, giving you the 2-Lo capability you’re searching for.

Those with 4x4s that feature non-disconnect front axles without locking hubs will have to either find a way to add manual-locking front hubs, modify the transfer case for a 2-Lo setting, or add a driveshaft disconnect, such as the Remco (remcodsc.com) driveshaft disconnect.

As an aside, some off-road enthusiasts like to have the ability of disconnecting the rear driveshaft while in low range. This front-wheel-only low-range capability, while typically reserved for competition and extreme wheeling applications, will help pivot the vehicle around extremely tight corners while dragging the rear brake. Most factory transfer cases can’t be modified for this type of capability. Although, some transfer cases can be converted with the use of aftermarket parts or garage ingenuity. Companies such as Offroad Design (offroaddesign.com), Trail-Gear (trail-gear.com), and Trail Tough (trailtough.com) offer components to allow some of the more popular transfer cases to be able to be shifted into front-only low- and high-range. For all-around universal shifting capability, the heavy-duty Advance Adapters (advanceadapters.com) Atlas transfer case can perform front dig duties and 2-Lo rear-only right out of the box without modifications. A Remco rear driveshaft disconnect could be used on the driveshaft in applications with no other viable options.

Easy Wheelbase Extension

Is flipping the leaf springs with offset axle perches an acceptable way to stretch a wheelbase?
@jaredwgraham
Via Instagram @cappaworks

Extending the wheelbase of a 4x4 became more popular as trail rig tire sizes got bigger and the trails and climbs got more extreme. Longer wheelbases are generally more stable and capable on climbs but less maneuverable in tight sections.

The short answer is yes, you can extend the wheelbase of your leaf-sprung 4x4 using these methods. Most 4x4 rear leaf springs feature an offset center pin, where the rear half of the leaf spring is longer than the front half. Flipping the springs around will move the rear axle rearward, extending the wheelbase. However, there are some exceptions in which this modification can’t be easily performed. In some cases, it’s not at all ideal because of excessive spring arch and the differences in bushings and mounting bolt diameters on each end. It’s much easier to flip flatter leaf springs. Heavily-arched springs will significantly alter suspension geometry and pinion angle when flipped. If it can be done in your application, flipping the springs around will offer 2 to 8 inches of rear wheelbase extension, depending on the leaf springs you are working with. This type of modification is usually done to the rear of a 4x4 to get a longer wheelbase on the cheap. You’ll still need to address any clearance issues around the rear axle, adjust the pinion angle, fabricate new shock mounts, get a longer rear driveshaft, and either relocate or install a longer rear brake line. Of course you’ll also have to trim, modify, or completely remove the rear fenders too.

In most cases, you can’t flip the front leaf springs without significant modifications on a 4x4 that has front leaf springs with offset center pins. The longer end is already behind the axle. Flipping the springs here will actually shorten the wheelbase and put the front tires too close to the cab.

Offset leaf-spring perches, such as those from RuffStuff Specialties (ruffstuffspecialties.com), can be used to fine-tune your wheelbase an inch forward or back. This can be helpful when trying to make room for larger axles and tires around fuel tanks, steering components, and wheelwells that can’t be easily trimmed. In most cases, the factory driveshaft, brake lines, and shock mounts can be retained, but you’ll still want to cycle the suspension and check for unacceptable component and chassis clearance.

Traction Controlled

Do people usually turn off the traction control on their Jeeps or other vehicles on- and off-road like I do? I recently picked up a ’12 two-door Jeep JK Wrangler and I find myself purposely turning it off because it doesn’t like threshold braking and my other driving habits. I’m used to older things.

My wife backed our two-wheel-drive ’17 Ram 1500 downhill to a gate to unload hay, and then called me and said the truck was stuck. So it sat there until I got home. I had to turn the traction control off to get it to keep the rear tires spinning and drive back up to the gravel road.
Keep up the good work!
Vince Hays
Via facebook.com/fourwheelermag

Unfortunately, the OE traction and stability control systems are here to stay. Some manufacturers have more advanced systems that are better tuned for off-road use and driving aggressively, while other vehicles are plagued with overly sensitive and annoying systems that pull power, apply the brakes, and light up the dash like a Christmas tree when you use the vehicle in a way it never expected. The good news is that traction and stability control systems have come a long way. The systems that were available only a few years ago are generally not nearly as good as what’s available today, especially in the sand, mud, and other loose or slick surfaces.

Most new vehicles have a pushbutton that gives the driver the ability to turn off the traction control. It’s not at all unusual for competent drivers to switch off the traction control system. However, in most cases, the system is not completely defeated when the button is depressed, it’s just made less sensitive. Too much tire spin will cause the traction control system to intervene. Some vehicles, such as the Ford Raptor, allow for the traction and stability control to be completely defeated, which for most drivers might not be the best idea. We’ve found that it’s kind of nice to have the stability control safety net, as long as the system isn’t overly intrusive. Although, there are still situations, such as in the sand dunes and on really slick mud, where we don’t appreciate the electronics trying to save us. In some cases, the systems can make extreme driving in these conditions more hazardous, especially if they pull power or apply the brakes at the least opportune time when performing a controlled aggressive maneuver.

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