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Answers to all your Jeep questions

Posted in How To: Tech Qa on June 21, 2017
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ZJ Splitter Swap

I was thinking about buying a 1997 Grand Cherokee with the 5.2L V-8 and Quadra-Trac transfer case. The only thing holding me back on this purchase is the full-time four-wheel drive. How big of a job is it to swap out this transfer case to a NP242 or the NP231? I will be performing all of this myself including rebuilding the donor transfer case. Thanks for the great magazine and all the tech articles.
Chris Didick
Homeworth, Ohio

The full-time transfer cases found in many of the Jeep Grand Cherokee ZJs and WJs are often accused of being unreliable, which couldn’t be further from the truth in most cases. In a stock application, the full-time NV249 Quadra-Trac transfer case found in the ZJ is easily good for 100,000 miles, and often much more than that. Of course, adding a lift and larger tires, along with aggressive off-road driving can shorten the life of your full-time Grand transfer case. It’s generally the viscous coupler inside the transfer case that gives up the ghost first. This is the sort of limited slip differential in the transfer case that allows for speed differentiation between the front and rear axles while in all-wheel drive. It is designed to transfer power where it is needed depending on road conditions and tire slip. The unit is locked when the transfer case is shifted into low range on the 1996 and later models, so using low range when driving off-road can significantly increase the lifespan of the viscous coupler in your NV249. It should go without saying, but running different sized tires on the front and rear of your NV249-equipped Jeep will lead to increased viscous coupler wear and eventual failure.

A viscous coupler will fail in one of two ways: it can stop engaging altogether or it can remain constantly engaged, which may depend on the operating temperature. The viscous coupler has a thick silicone liquid inside that becomes almost a solid when exposed to the shear force introduced by the front and rear output shafts rotating at different speeds. The most common cause of viscous coupler failure is fluid loss through leaking seals. Fluid loss will keep the viscous coupler from engaging and your Jeep will no longer have four-wheel drive. The more potentially costly failure occurs when the coupler remains engaged when it shouldn’t be. If you continue to drive it on the street with a locked up viscous coupler, you could do damage to the driveshafts or axles. Excessive tire chirp and crow-hopping during cornering on the street are good indicators that your viscous coupler is locked up.

If you are keeping the Jeep stock, don’t discount the NV249. All of the rebuild parts are available from companies such as Crown Automotive (crownautomotive.net), including new viscous couplers. Rebuilding the NV249 is relatively easy and similar to rebuilding the any of the NV chain-driven transfer cases.

If you decide to swap out the NV249, you can switch to an NV231 with relative ease. The NV231 has the same six-bolt pattern as your NV249, so no adapter is required. However, you’ll need to make sure you install the proper length input gear in the NV231 to match up to your stock transmission. Companies such as JB Conversions (jbconversions.com) and Novak Conversions (novak-adapt.com) can provide the proper input gear as well as NV231 rebuild kits. You will also need to modify the transfer case shift linkage and driveshafts to work with the NV231.

Track Bar Troubles

I hope you can help me or at least point me in the right direction regarding a steering story from an older issue. (“Crossed Over” Oct. ’09). The photos did not give any clear information for this 77-year-old retired British mechanic.

Most steering woes can be blamed on the length and mounting position of the draglink in accordance with the front track bar. It doesn't take much to disrupt the geometry. I want the track bar and steering linkage on my WJ to be parallel and the same length. How is this possible? Someone must have done this before and I do not want to reinvent the wheel. I would really appreciate your help in any way.
Brian Knight
Via email

All of the coil-sprung Jeeps including the XJ, ZJ, WJ, TJ, and JK have a track bar on the front axle that needs to work in conjunction with the steering linkage, and specifically the draglink. In a stock application everything is designed to work harmoniously with no bumpsteer. If the mounting locations and lengths of the draglink and track bar are altered indiscriminately, it can result in bumpsteer, which can make the handing of your Jeep questionable at any speed over rough surfaces.

Now, in order to prevent bumpsteer, these linkages don’t necessarily need to be perfectly parallel to the ground (although it is ideal). They only need to be parallel to each other. Some low-cost lift kits will disrupt the steering geometry by including only a dropped pitman arm and not the brackets required to drop the front track bar by the same amount, which of course results in bumpsteer. Other lift kits simply allow the draglink and track bar angles to increase to the point that it causes other adverse handling problems and tie rod end binding. If either of these situations is what has happened to your Jeep, there are several ways it can be fixed depending on the Jeep model. For your WJ, take a look at the WJ Steering Equalizer from Iron Rock Off Road (ironrockoffroad.com). It drops your track bar three inches on the frame side to match the dropped pitman arm of a lifted application. It also runs under the oil pan and to the other side of the unibody frame structure for extra support and increased chassis rigidity. Dropping the frame side of the track bar to match the drop pitman arm will provide steering and handling performance that is similar to stock. Kevin’s Offroad (kevinsoffroad.com) offers the Iron Rock Off Road WJ Steering Equalizer with a dropped pitman arm as a complete kit.

Bad Vibes

I have a 2001 TJ Wrangler with a 4.0L, automatic transmission, and NV231 transfer case. There is a vibration that happens between 35 and 43 mph, no matter if I'm accelerating or slowing down. It started after a trail ride last year. It feels like the transmission skidplate is vibrating.
Gerald Hall
Via facebook.com/JohnCappa4x4

There really are only a few places that can produce annoying vibrations on a Jeep. Being able to track down the vibration happening after an off-road excursion is also helpful.

The first possibility is that you simply have a broken motor or transmission mount. It’s not uncommon for older mounts to fail when driving off-road. The extra torque from low-range and a flexing chassis can cause worn mounts to simply give up. Inspect them and replace anything that looks rotten, cracked, or worn.

Another possibility is that you high-centered your Jeep or hit the transfer case skidplate pretty hard on a rock or other obstacle. If so, you may have bent the skidplate, which doubles as the transmission/transfer case mount. If it’s bent enough, it could cause the driveshaft angles to be off, leading to a driveline vibration. A factory replacement skidplate is available from Crown Automotive (crownautomotive.net). A better option is to replace your bent weak stamped-steel factory skidplate/crossmember with a heavy-duty aftermarket skidder which is available from companies such as Genright (genright.com), Nth Degree Mobility (nthdegreemobility.com), Rusty’s Off-Road (rustysoffroad.com), Skyjacker (skyjacker.com), and TeraFlex (teraflex.com). As an added bonus, many of these are designed to provide increased ground clearance over the stock skidplate.

It’s also possible that your problem is driveshaft related. You could have rubbed the driveshaft on a rock and peeled off the balance weights, dented a driveshaft tube, or bent the driveshaft. If you see dings and scrapes on the driveshafts, you’ll probably need to remove them and have them retubed, or at the very least rebalanced.

Lastly, it could be that the off-road excursion had nothing to do with the vibration. Sometimes things just wear out. You might have a worn U-joint or CV joint in the driveshaft. Also check the control arms and bushings. If the arms are bent or the bushings worn, that could cause the axle to rotate imperfectly and throw off the U-joint angles, which would lead to driveline vibrations.

It’s always a good idea to give your Jeep a once-over as soon as you’re home after being on the trail. Fresh impacts and damage to components is usually a lot easier to find than something that has had time to accumulate dirt and grime.

Leaf Layout

I have been following your GPW build (“Garage Project GPW”) as it has been an inspiration for my own 1947 CJ-2A. I have a tech question regarding setting up proper leaf spring shackle angles and locating shackle hangers and brackets. The front axle is a Dana 44 from a 1974 Wagoneer and the rearend is a metric Dana 44 from an Isuzu Rodeo. I am using Rubicon Express 4-inch-lift YJ leaf springs and will keep it spring-under. I am using RuffStuff Specialties spring mounts. How do I begin figuring this out or should I simply locate the leaf spring shackles and hangers the same as on a stock YJ? Also, how would you recommend setting up the shackle angle? Can I do this without the drivetrain and body tub on the frame or should I have these mounted for weight reference, and what would be the correct shackle angle?
Terrance Duchcherer
Via facebook.com/JohnCappa4x4

In order to locate the leaf spring pivots and shackle mounts, you'll need to decide where you want the axles to be located in reference to the frame and wheelwells at ride height first. Then you'll need to make sure your selected tires will clear based on that chosen location. Keep in mind that the axle will move forward and backward during suspension compression and droop, especially with the arched leaf springs you are using. The front to back movement can cause clearance problems. You'll also need to consider driveshaft angles when selecting the wheelbase.

You'll likely want to run the Wagoneer front spring width and simply use the factory front spring perches that are already on the front axle.

You can either start by locating the springs on the frame, or bolting them to the axle. If you choose to bolt them to the axle prior to locating the brackets on the frame, you'll need to make sure the leaf springs are perpendicular to the axlehousings prior to cinching down the U-bolts.

The shackle angle you set up will depend on the springs, the length of the shackles, and vehicle weight. Based on what you are working with, I would try setting them up at about perpendicular in relation to the frame with the springs in static position and unloaded. This will give you the ability to mock it up with just a bare frame. The shackle will kick outward quite a bit as the arched spring lengthens during suspension compression. If the shackles kick back and bind during droop, you can either limit down travel or you can build shackle stops to keep the shackles from swinging inward too far.

Willys Steering Swap

I've got a few questions about the steering box you've used on the Garage Project GPW. What did it come out of and could you send me a few pictures of it? I'm building a Willys truck and would like to update my steering.
Taylor Perosio
Via facebook.com/JohnCappa4x4

The quick-ratio steering system on my GPW is kind of an odd combination of parts for a recreational Jeep. It’s a little bit of an experiment really. However, the GM 800 model steering gear that I’m using is not at all uncommon. Versions of it can be found on GM and Jeep vehicles from the 1960s through the 1990s. The steering gear I chose is from a 1979 Camaro. There are two models available for that particular vehicle. One version offers a lock-to-lock of 3–4 turns of the steering wheel and the other has a much faster ratio with 2.5–3 turns lock-to-lock. Of course there are many other viable GM 800 steering gears available. Most are around 3.5 turns lock-to-lock. Various hydraulic fitting sizes and two different input sizes were used over the years on these steering gears, so they are not all interchangeable. Metric fittings started surfacing in the early 1980s and the larger input started disappearing in the mid-1970s. Most of the earlier GM 800 steering gears feature four threaded mounting lugs for 7/16-inch bolts. Later boxes only feature three mounting lugs, which is fine for all but the most extreme applications. The larger and heavier cars came with heavy-duty steering gears with a slower ratio and a larger piston for more assist. So if you are looking for easy one-finger steering, look to the larger GM cars like the Cadillac Eldorado or Jeep J-20 pickup.

Choosing a steering gear has more to do with personal preference than anything else. My setup is designed to have very few turns lock-to-lock. I don’t enjoy juggling the steering wheel when speeding down a dirt road. Some people think that quick-ratio steering gears make your Jeep feel twitchy and unstable. I’d argue that the slower more powerful boxes provide a vague steering feel on- and off-road. I personally like to have a little bit of input from the road. Companies such as AGR (steerco.com), Howe (howeperformance.com), Lee Power Steering (leepowersteering.com), and PSC (pscmotorsports.com) offer high-performance steering gears for on- and off-road applications. If you have very specific steering needs, these companies can provide solutions that are more advanced and powerful than what a remanufactured factory steering gear can offer.

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