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Answers to all your Jeep questions

Posted in How To: Tech Qa on April 14, 2016
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Grand Overland
I just picked up a ’02 Grand Cherokee 4x4 with 150,000 miles. It has the 4.0L inline-six and a Selec-Trac NV242 transfer case. Is this a reasonable and durable transfer case? Is it as tough as a NV231? I want to build the Grand as a commuter, overlander, and trail rig. I want it mild but still fun. Any suggestions? I was thinking 31-inch tires. I already have a TJ on 37-inch tires for more extreme wheeling.
Mark Richter
Via facebook.com/JohnCappa4x4

The ’99-’04 WJ Grand Cherokee is a great platform for a mildly built adventure 4x4. The sensibly sized tires and short lift are a good plan to help maintain reliability, provide good on-road handling characteristics, and to keep build costs down. Since you’ll likely be adventuring far into the outback, you should give the vehicle a really good inspection. Look for loose or worn suspension and steering components. Some of the key inspection areas are the wheel bearings, ball joints, steering linkages, front track bar ends, and rear upper arm ball joint. Anything that looks questionable should be replaced.

The WJ Grand came with either the 4.7L V-8 or the venerable 4.0L inline-six. For your planned use, I think the 4.0L is the better choice. In contrast to the 4.7L V-8, the 4.0L is very simple and pretty much any auto parts store will have the regular maintenance items in stock. The 4.7L isn’t a bad engine, it’s just very complex and if something major goes awry, it could be an expensive repair. The more powerful 4.7L would be a better option for someone that plans to tow a trailer or install much larger tires.

An NV242 Selec-Trac transfer case has several shift options, making it a great transfer case for a variety of on- and off-road conditions. It has 2WD (two-wheel-drive), 4PT (part-time four-wheel-drive), 4FT (full-time four-wheel-drive), Neutral, and 4LO (four-wheel-drive low range) shift settings. The 2WD and 4FT settings are generally reserved for street use. For best fuel economy you can shift into 2WD. If the paved roads are wet or a little slick with sporadic icy patches, the 4FT full-time 4x4 setting is extremely handy. The 4PT and 4LO settings are for slippery and loose surfaces only. The NV231 transfer case is a little more durable but not as versatile as the NV242. You likely won't have any issues with the NV242 as long as you keep it filled with the proper oil and repair any leaks. If you want the ultimate in durability, consider a slip-yoke eliminator conversion kit and rear CV driveshaft from Tom Wood’s Custom Drive Shafts (4xshaft.com). You’ll need to alter the rear pinion angle for fitment, but this can be done with optional adjustable lower control arms available from companies such as JKS Manufacturing (jksmfg.com).

Since a WJ Grand Cherokee on 31-inch tires still sits a little low compared to most trail-friendly 4x4s, I’d recommend a good set of rocker guards to protect the body sides. Companies such as Kevin's Off Road (kevinsoffroad.com) offer solid rocker protection. The extra tube step provides additional coverage and helps to protect the Jeep from potential door dings in the parking lot and on the trail.

Protecting the underside is also a good idea if you plan to encounter rocky trails. Kevin’s Off Road offers a 1/4-inch-thick plate steel transfer case skidder that features a rigid seven-bolt mounting design.

Wrangling Rear Driveshaft
I have a ’92 Jeep YJ that has lockers, a spring-under lift, 35-inch tires, a slip yoke eliminator, and a double-Cardan driveshaft in the rear. I got a little rough with it in Parker, Arizona, on a fairly steep hill. I hit a rock at the top just as I started to go down. The rock must have hit the driveshaft, and it came off while going down the hill. It flung around and beat up everything underneath. I had to be towed out because the trail was so rugged. When I got it home, I ordered a new axle yoke and U-joint. After installation I went on a test drive. I broke off the yoke tab, the U-joint came apart, and threw the driveshaft. It beat the bajesus out of the stuff underneath again. I ordered a new yoke and U-joint from Tom Wood's Custom Drive Shafts and put those on and it has failed yet again. The original owner had the work done on the Jeep by MIT in El Cajon, California. I drove the Jeep for many years until this incident with the rock at the top of the hill. Have you ever ran across a problem like this? I included a photo of my rear driveshaft setup. Any and all help would be appreciated!
Trennis Wright
San Diego, CA

If everything was working fine for a long period of time, prior to the first failure, it sounds like you may have bent the driveshaft when it came off the first time. A bend or dent in the driveshaft could cause the problems you are having. I recommend taking or sending out the driveshaft to a reputable shop to have it checked for balance and straightness. The other (unlikely) possibility is that you bent the pinion shaft. However, if this had happened, you would likely have a pretty severe pinion seal oil leak.

The photo is very telling. It looks like you have an axle-wrap problem. The leaf springs are bent into an S shape around the spring perch. The pinion angle is also incorrect. It looks like it’s pointed too far up. The yoke should be pointed directly inline with the driveshaft so the U-joint on the axle end operates at 0 degrees or maybe 1-2 degrees down to compensate for normal axle-wrap. The bent springs could be the reason for the incorrect pinion angle. It’s also possible that the leaf spring U-bolts are loose, which would allow the axle to rotate under torque and cause the issues you are having. The axle movement is likely causing the driveshaft to bind enough to damage the yoke and U-joint retaining hardware. I would recommend replacing the leaf springs, preferably with some that have more than four leaves. You’ll be better off with a thicker pack made from thinner leaves. You might also consider a leaf pack with a good warranty—you’re clearly a little hard on parts. BDS (bds-suspension.com) offers a no-questions asked lifetime warranty on leaf springs. While it’s apart, inspect the leaf spring perches for damage, if they look smashed and rounded, they should be replaced. Once you get it all back together, check the pinion angle and adjust the perches prior to welding them in place or use the correct axle shims. Steel axle shims from companies such as Rocky Road Outfitters (rocky-road.com) will hold up much better than the aluminum shims. Aluminum shims can crack over time and fall out, leaving the leaf spring and U-bolt assembly loose.

Diesel Flatfender Planning
I'm totally new to this and doing a lot of reading about off-roading. I've always loved the flatfender Jeeps, and I think I want to build a CJ-3A from scratch with a new frame. I’ve been reading the Garage Project GPW flatfender articles in Jp. I love what you did with the Land Rover suspension bits on your flatfender and plan to copy that. My question is about axles and gears. I intend to use it as an overland expeditionary type Jeep, not a mud truck or a rockcrawler exclusively. I'd also like to do a large amount of on-road driving as well. I think I want to build in disc brakes and power steering. What axles should I buy and what gears should I put in them? I’m not sure if I want 31-inch tires or 33s. I'm leaning towards the 1.9L VW TDI diesel engine. I chose the VW diesel to take advantage of the fuel economy, power, and torque. I figured it would be disastrous for me to take on the selection and installation of the transmission and transfer case myself; which is why I have elected to take the Jeep to Coty Built.
Joe Garcia
Via facebook.com/JohnCappa4x4

The axles and gears you select for any project depend greatly on the tire size you plan to go with, the powertrain, and the overall weight of the vehicle. I think you could easily get by with a Dana 30 front axle from a ’76-’82 narrow-track CJ. The ’82.5-’86 Wide-Trac CJ axles might be a bit wide for what you want to do, but they could work. Out back, you have lots of options, but what you chose will again depend on the engine, transmission, transfer case, lift height, tire size and so on. You'll most likely want a low-pinion Dana 44. But if you are using the stock Spicer 18 transfer case, you'll need an axle with a differential that is offset to the passenger side. So an early ’70s FSJ Jeep Wagoneer axle like the one I'm using in the Garage project GPW might be a good choice depending on the width of your front axle choice. Custom axle manufacturers such as Currie Enterprises (currieenterprises.com) and Dynatrac (dynatrac.com) can build complete axle assemblies to match nearly any specs you require.

You'll likely want a numerically lower (numerically higher) axle gear ratio than you would use with a gas engine to compliment the low rpm power of the diesel. Also, if the transmission has an overdrive, you can go a little higher with the axle gears and still maintain roadworthiness. You should take a look at a gearing calculator to figure out what rpm the engine will spin at given your desired highway speed. Randy’s Ring & Pinion (ringpinion.com) has an easy to use gearing calculator that can work an overdrive transmission into the equation. I believe a stock 1.9L VW TDI would prefer to cruise at around 1,600 to 1,900 rpm. Given an overdrive automatic transmission, 31-inch tires and a cruising speed of 65 mph, I suspect you'll want to be somewhere around a 3.00:1 to 3.50:1 axle gear ratio, but you may even prefer something around a 2.75:1 ratio if you desire a faster cruising speed. Coty Built (cotybuilt.com) specializes in high-performance TDI modifications. If you up the power from stock, you might need to play with the gearing calculator a bit more to help select the best ratio for the cruising rpm of the performance-enhanced engine.

Be sure to check the overall length of the engine, transmission and transfer case you select, there isn't a lot of space to work with on a flatfender. I often joke that where you mount the steering box could alter where the real axle needs to be located. Keep in mind that some of the more modern aluminum transfer cases are far too wide for the narrow flattie frame. The cast iron Dana 300, Dana 20, and Spicer 18 transfer cases are a snug fit if you are using a stock-width frame.

Jeep T-18 Swap
I can't seem to find definitive information regarding swapping inputs on an FSJ T-18. I want to put the FSJ T-18 into my CJ-5, and I have found a guy that has an OEM CJ T-18 input shaft for $95 shipped. Would that swap in without any extra parts? I’m aware of Parts Mike's short input swap kit, but as always I'm trying to save some money. If I can get away with just the input and maybe a bearing or something, I'd like to try it without shelling out $200 for the entire kit.
Evan Knapp
Via facebook.com/JohnCappa4x4

The T-18 manual transmission was used in many different vehicles including Fords, International Harvesters, and Jeeps. There are a lot of different variations, so swapping parts from one version of the transmission to another isn’t always possible or as easy as you might think. There are said to be 12 known Jeep versions of the T-18 transmission used from 1966 to 1984. The most common variation is in the input shaft configuration and gearing. If you don’t know exactly where the input shaft originally came from, it could be a $95 gamble and a big waste of time and money.

Generally, most ’72-’75 CJ T-18s came with the 4.02:1 First gear and were fit with a cast-iron front adapter plate for the AMC bellhousing. The ’76 model was a crossover for the Jeep CJ T-18. It could have had the 4.02:1 or 6:32:1 First gear and it did not have the front adapter. All CJ T-18s from 1977 to 1979 have the wide-ratio and 6.32:1 First gear without the front adapter plate. These are the shortest of the Jeep input shafts, measuring 7.43 inches of stickout. The Jeep CJ T-18s from 1976 to 1978 should be cast with 13-01-097-907. The ‘79 Jeep CJ T-18 is similar to the ’76-’78 versions, except that it has a wider front bearing, a different top cover with aluminum shift forks and a different shift pattern. These T-18s usually have a case casting number of 13-01-065-904 and a top cover casting of 13-01-065-906.

All FSJ T-18 transmissions feature varying lengths of input shafts, which are usually too long for installation into short wheelbased Jeeps. They were fit with a variety of factory adapters and deeper bellhousings. Lots of people get caught up in fruitless searches for the rarest of the Jeep T-18 input shafts and bearing retainers. Fortunately, both Novak Conversions (novak-adapt.com) and Parts Mike (partsmike.com) offer a short input shaft kit for the wide ratio (6.32:1 First gear) Jeep T-18. I don’t know of a kit for the narrow ratio (4.02:1 First gear) Jeep T-18. Ultimately, you are likely far better off with one of these proven kits that include all the new hard parts and gaskets you’ll need to make the swap, rather than a questionable used input shaft alone.

Splining
I have a ’07 Wrangler Unlimited X 4x4, and I want to put a locker in the rear axle. I need to know if it has 30- or 35-spline axleshafts so I can order the correct locker. The Jeep has a Dana 44 with a 4.10:1 gear ratio. It’s the stock axle that came with my non-Rubicon Jeep.
Raul
Via email

The non-Rubicon ’07-’15 Jeep Wrangler Dana 44 rear axle features 1.31-inch-diameter 30-spline axleshafts. The 1.50-inch-diameter 35-spline locker is for use with heavy-duty aftermarket axleshafts such as the JK44 Axleshaft Upgrade Kit from Dynatrac (dynatrac.com). If you plan to add larger tires and off-road regularly, you may want to consider upgrading the axleshafts at the same time you add the locker. If you decide to stick with the 30-spline shafts for now and make the switch to 35-spline shafts at a later date, you will need to buy a completely different locker. You cannot upgrade the 30-spline locker to 35 splines.

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