Techline: Your Top 4x4 and Off-Road Tech Questions Answered HerePosted in How To: Tech Qa on December 20, 2018
Rubicon Front or Rear DriveAssume you have a typical Jeep, say a JK on 35-inch tires. You have to run the Rubicon in two-wheel drive. Would you choose to run rear-drive only, or front-drive only, and why?
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I can’t imagine doing this on purpose, although given these parameters it would have to be something done purposely. You typically don’t get to decide which axle fails to transmit power to the ground in the middle of a trail. Regardless, I’ll go ahead and assume that you won’t let me switch from front- to rear-wheel drive when I want to, depending on the obstacle in front of me. Given that I have to stick with my choice through the entire trail, I’m going with rear-wheel drive. I’d also air down all four tires to 8-10 psi or less depending on the make, model, and size of the tires and wheels. The lower tire pressure will not only increase traction, but the aired-down tire carcasses will be more compliant and roll more easily over rock obstacles that would otherwise act as wheel chocks and stop the vehicle in its tracks.
Now, the answer as to why would I choose the rear drive over the front is simple, but with several important reasons. First and foremost, my concern would be for survivability. If my 4x4 breaks, I’m stranded on one of the most famous and difficult trails in the United States. Breaking down on any trail seems like a bad idea, so I typically take all the precautions necessary, regardless of the fact that in this case I’m already starting out with a 4x4 missing two legs. Having said all of that, the OE rear axle of any 4x4 is typically stronger and more durable than the front axle. These vehicles are designed to drive nearly their entire lives on-road, and in some cases even tow a trailer in rear-wheel drive. To accommodate this added stress and wear, the rear axle components are always larger than the parts found in the front axle on the same 4x4. Of course, there will be very specific situations on the trail where front-wheel drive would be better to have than rear-wheel drive, but they are few. By comparison, the rear-wheel drive will be much more beneficial, especially when climbing. The weight transfer to the rear axle when climbing up and over an obstacle will help in the rear traction department, where an unweighted front-driven axle might flail around uselessly.
There are some places I’d likely have to use a winch or a buddy to pull me up. But realistically, most of the Rubicon Trail can be traversed in 2WD in a capable Jeep with properly aired-down tires.
Long-Travel TTB or SwapI have a ’95 Ford F-250 diesel with a Spacekap camper. I’m building it to camp and tow. Should I build up the TTB axle into a long-travel setup? Would that be a good axle for highway use and towing? Or should I swap in the Dana 60 that I have from the same year truck? Either way, I have to replace the springs. Any advice?
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If the TTB is functioning and no parts are worn, there really is no need to upgrade the front axle in your application. Widening the front beams and installing long-travel coilovers and bypass shocks won’t do you much good without addressing the rear suspension too. You will have to tune the long-travel suspension for the weight you plan to have. Tuning the long-travel suspension for the added weight of a trailer or camper and gear will generally provide poor performance off-road when not towing or hauling camp gear. I think the stock suspension along with some quality monotube shocks that feature compression adjusters would serve you well. The TTB front suspension will offer a smoother ride than the solid front axle on- and off-road. However, if you are looking for the ultimate in durability, are sick of the strange tire wear that the TTB setup provides, or your TTB axle and suspension are due for an expensive overhaul, then the Dana 60 solid-axle swap might be a good plan.
Two-by-Four ConversionI’m swapping a TH400 transmission and an NP208 transfer case into my ’71 GMC C25 after I do a solid-axle swap. Is there a slip-yoke eliminator kit available for the NP208 or should I stick with a stock-type driveshaft, in which case, is the slip-yoke at the transfer case end a limiting factor for rear wheel travel? Is a custom driveshaft in order?
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The need for a slip-yoke eliminator on your NP208 transfer case will ultimately be determined by the length, angle, and plunge requirements of the rear driveshaft. Shorter wheelbases and bigger lifts will dictate the need for a slip-yoke eliminator. The traditional slip-yoke also doesn’t do well with long wheel travel suspensions. If after cycling the suspension and checking the angles and driveshaft plunge you find that a slip-yoke eliminator kit is needed for your application, Tom Wood’s Custom Drive Shafts (4xshaft.com) offers a slip-yoke eliminator kit for the 32-spline NP208. The bolt-in kit uses a modified stock output shaft and speedometer housing. Transfer case disassembly is required for installation.
Another option is to go with the slip-yoke eliminator from Driveshaft Superstore (driveshaftsuperstore.com). This slip-yoke eliminator features a fully splined 1 7/8-inch seal surface and a universal flange that has a Ford 3-inch square hole threaded pattern, Chevy 3-inch square hole pattern, Toyota 2 3/8-inch square by 2 11/16-inch CV hole pattern, and the Suzuki large hole pattern. The new flange bolts to the original transfer case rear output shaft after drilling and tapping a hole in the center. In most cases, no transfer case disassembly is required.
Your third option is to go with a different transfer case, such as the NP205, many of which will already come with a fixed rear output yoke. If you have trouble locating a good NP205 ready to bolt to a TH400, Offroad Design (offroaddesign.com) offers completely rebuilt NP205 transfer cases with no core charge. The company also offers a heavy-duty version of the adapter required for the swap. If you plan to throw a lot of power and excessively large tires at this truck, the NP205 swap might be the best route, especially if you are an aggressive driver.
10-Hole DilemmaI have a ’00 Ford Excursion. I swapped out the front axle for a ’02 dualie axle minus the dualie extensions. I want to run 41-inch Continental tires. I am running 3-inch spacers. Will the spacers hold up to the new tires? Should I buy the dualie hub extensions or should I swap the axles for F-450 10-hole axles? If I do go with the F-450 axles, is the 10-hole bolt pattern the same as the military bolt pattern on HEMTT wheels?
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If you are hauling any kind of load or off-roading regularly, I think the wheel spacers are a bad idea on a heavy 4x4 like this. The good news is that you don’t need to swap out the axles to get the 10-hole lug pattern. You can use the dualie wheel ends and the factory Ford F-450 10-hole wheel adapters or purchase the 10-hole wheel adapters from companies like Mr. Lugnut (thewheelgroup.com), part number WA02‑8170F. These 10-hole wheel adapters convert the Ford dualie 8-on-170mm lug pattern to a 10-on-285.75mm (10-on-11.25) lug pattern. The HEMTT wheels and tires are not be the best choice. They are incredibly heavy and will sap overall power and braking performance. A single steel wheel alone is 152 pounds! The 8.89 inches of backspacing is a lot, but could work with the correct adapter. You could also recenter the wheels, change the backspacing, and alter the lug pattern if you were determined to run these heavyweight wheels. The good news is that Hutchinson Wheels (hutchinsoninc.com) offers lighter 20-inch-diameter wheels that can be easily fitted to your Ford with the correct dualie wheel hubs and adapters.
Big-Block TBIIs it possible for a factory GM TBI setup to feed a mildly built big-block pushing 400 hp and 550 lb-ft of torque? I’m wondering if I should go this route for the ease of finding parts should something happen versus one of the aftermarket four-barrel EFI units.
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The GM big-block V-8 engines were available with a factory TBI fuel injection system through 1991. Of course, these engines maxed out at around 255 hp and 405 lb-ft of torque. However, the TBI system can be easily modified to support more power, such as in your case. If you prefer to use the factory GM EFI components, contact Howell EFI (howellefi.com). The company offers compete GM-based bolt-on TBI systems for the carbureted 454ci and 502ci engines.
For more even more powerful big-block engines, Howell EFI offers a twin TBI kit. This kit is designed to convert any oval-port Chevy 396ci–502ci engine from a carburetor to twin throttle body fuel injection. It includes two remanufactured GM TBI units and a new Edelbrock 2x4 intake manifold made specifically for oval-port big-block Chevy engines. A wiring harness, GM ECM, all required sensors, and an inline high-pressure fuel pump are included. The optional ignition control comes with a new electronic distributor, coil, and knock sensor. The components can also be ordered separately for use on any GM, Ford, or Chrysler engine with a 2x4 intake manifold designed for Carter AFB or Edelbrock carburetors.
FJ Axle UpgradesAre there any rear aftermarket axleshafts you would recommend for a Toyota FJ45?
My brother-in-law keeps breaking them. I suspect it’s due to the big, heavy 33x12.50R15 tires he’s using.
Gustavo Villalobos Luna
The C-clip rear axleshafts found in many of the Toyota FJ Land Cruisers aren’t notoriously failure prone with only 33-inch tires. Although, adding a lot of cargo weight, swapping in a more powerful engine, and driving aggressively can take their toll on the factory rear Land Cruiser C-clip axleshafts. The easiest upgrade would be to install a full-floating axle kit. A full-floating axle kit would take the vehicle weight off of the axleshafts and place it on the axlehousing via a spindle, similar to the way it’s done on most 3/4- and 1-ton truck rear axles. Full-floating axleshafts are only required to transmit power from the differential to the wheels, which reduces the stress on the axleshafts. Front Range Off-Road Fabrication (frontrangeoffroadfab.com) offers a bolt-on full-floating rear axleshaft kit for the Toyota FJ40, which should work on your FJ45. Specter Off-Road (sor.com) also offers a full-floating axle kit that fits the FJ Land Cruisers. If the entire rearend in your FJ45 is suspected to be bent or damaged, Specter Off-Road offers a full-floating rear axlehousing and axleshafts that fit the Toyota FJ40, FJ45, and FJ55 Land Cruisers. The used full-floating rear axle assembly does not include the third member or brake components. They are straight take-outs. You will need to reuse your differential and brake components to go this route.
Twitchy TrailerI’ve got my 4x4 up on a U-Haul car trailer. I towed it to work this morning, and then this afternoon I’ll start the trip from Arizona to California. When I was towing today, the trailer got some sway at about 70 mph when I would switch lanes. The swaying went away if I slowed down, but it made me uncomfortable. I noticed that my current hitch is a little high, and the trailer slightly points up at the front. If I put a hitch on with more drop, would that help? I have the 4x4 pulled all the way forward, with the tires all the way up to the front. I’ve got no problem spending the few bucks to buy a hitch with more drop if you think that will help.
It sounds as though you have a textbook trailer tongue weight issue. You don’t have enough weight forward of the front trailer tires. You have likely found that the sway will be worse under float throttle and coast conditions, such as coasting down a hill off-throttle. The lower the speed that the swaying happens, the more weight you need to move forward. In most cases, the tongue weight with a traditional bumper or receiver hitch should be 10-15 percent of the total trailer weight and 25 percent of the total trailer weight on fifth-wheel and gooseneck trailers.
Ideally, the trailer should be level, or close to it. The correct drop hitch will help a little, but you’ll likely need more tongue weight. You can compensate for the trailer tilt a little by pulling the vehicle on the trailer forward 6-8 inches at a time, which adds more tongue weight and compresses the rear suspension on the tow vehicle, leveling the trailer. Unfortunately, this is not an option for you since the trailed vehicle is already all the way forward on the trailer. You may need to move some weight around. Can you move weight from the rear of the towed vehicle and add it to the front of the trailer, to the front seats, or even to the bed of the tow rig? Removing any weight from behind the rear trailer tires will be helpful. Loading steel shot or weights to the front of the trailer will help too. Even a couple hundred pounds will make a difference. You could also temporarily relocate the spare tire from the back of your towed 4x4 to the front of the trailer. In some rare cases where the rear of the 4x4 is heavier or shorter than the front, it might benefit you to load the vehicle on the trailer backward. You’ll have to experiment to get the proper tongue weight for safe handling down the road.