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April 2007 4x4 Tech Questions - Tech Line

Posted in How To: Tech Qa on April 1, 2007
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Question: I own and wheel an '02 Jeep WJ Grand Cherokee and have issues with the NP242 Selec-Trac transfer case. Here's the lowdown: 5-inch lift, 33-inch M/Ts, locker front and rear, engine mods, lots of custom metal work, 4.0L engine and 42RE transmission.

My transfer case is giving up on me, and I was wondering if it was possible to take out the NP242 and replace it with a NP231? The reason I was thinking of doing this is the availability of the 4:1 kit for the NP231 and the reliability of the NP231 and to keep the weight down (compared to an Atlas II). What are your thoughts on this? Will it work?
Mike Sutherlin
Orlando, FL

Answer: I spent a lot of time checking out this swap and wasn't able to find much out about it, mainly because most people want to swap their 231 out for a 242 due to the advantages it has. In fact I even want to swap my 249 out of my own '96 Grand for the 242. My guess is that it should be a direct bolt-up since your WJ has the 4.0L motor. If it was the V-motor, then yes, you might have to disassemble both cases and swap the input gear from the 242 into the 231.

Yes, the 231 offers you the advantage of going to a 4:1 low range, but I think that the advantage of the ability to select so many combinations of drive outweigh the swap. Tom Wood's Driveshafts ( has a tailshaft conversion kit for the 242.

Question: My '01 Super Duty has a V-10, auto trans, and 3.73:1 axles. Since I put 285/75/R16s tires on, it runs 2,000 rpm at about 65 mph. I can currently squeak by with 15 mpg with a super-light foot. I have read in your magazine that if you go to a bigger tire, you should change your gears. If I don't do any crazy four-wheeling or tow anything worth mentioning, is it really necessary to go to lower gears? (Can you guys remember when you didn't think twice about mpg?)
Kenneth Branscum
FOB Summerall
Bayji, Iraq

Answer: Ford built the Super Duty with the idea that everyone who buys it will eventually tow or haul a heavy load, and they don't want them to be disappointed with the truck's ability to do so. However, they also wanted the truck to maintain the maximum fuel economy as well as minimum emissions, so the gear ratio is a compromise.

When one installs larger-diameter tires on a vehicle, it effectively raises the overall gear ratio. This, in turn, can sometimes put the engine out of the proper powerband that the engineers designed it to work in, especially when the truck is loaded. This gives the impression that the engine is not putting out as much power as it used to. The power output of the engine has not changed-you're just not operating the engine at the same rpm as before, and power output is in many ways related to engine rpm. That's what they make transmissions for.

If you're happy with the way your truck performs, and you are willing to grab a lower gear when hauling a heavy load, go a bit slower up a hill, and fuel mileage has increased, then there is not a problem. A decrease in fuel mileage is a pretty good sign that a lower gear is needed as it's an indicator that the motor is working harder than it was designed to do.

Something to keep in mind is that usually, when taller tires are installed, the tires are also wider, which means more rolling resistance. Combine this with some sort of a "lift kit" for the additional necessary tire clearance and this means more of the underside of the vehicle is exposed, which results in what is commonly referred to as "wind resistance." These factors all contribute to making the engine work harder for a given vehicle speed, so to compensate for it, a lower axle gear ratio is recommended.

Another reason for a change in axle ratio is that the "computer" in late-model vehicles reads engine rpm versus vehicle speed versus wheel speed and analyzes all this information to set certain parameters as to how the engine runs, the transmission shifts, and the braking system works. Generally speaking, changing to a tire size within less than 10 to 15 percent of the original OEM size does not have any effect on the system.

If you're happy with the fuel mileage gain and the way the truck performs, then I don't see any problem with the present combination.

Question: I am building a Jeep YJ with a spring-over lift with a BDS 3 1/2-inch lift kit and a 2-inch shackle lift. I will only be driving this vehicle on the sand dunes in Michigan and it will never see the road again. I have Chevy 3/4-ton axles, so my question is, would it be possible to avoid crossover steering by fabricating a mount on the outside of the frame and using a steering box from a Chevy truck with a dropped pitman arm and drag link? As I said, I will not drive it on the road so there is less wear on the steering.
T Boulter

Answer: Well, there are a couple of issues here that concern me. First, why so high up in the air? The spring-over will give you about 5 inches; add on the 3.5 inches of spring lift and the 2 inches of shackle lift, and wow! That puts the Jeep way up in the air. For sand running, I like my Jeeps as low as possible while still maintaining enough clearance for the tires to fully articulate.

Secondly, why go to the trouble of trying to figure out how to mount a steering box outside of the frame? I would think that it would be best to keep the original Jeep box, use a dropped pitman arm, and go to crossover steering. It will work so much better than what you had planned. Yes, with the Jeep sitting as high as you plan, you will have a bit of angle on the drag link, but most likely you can live with a bit of bumpsteer when out in the dunes.

Question: I have a '92 Chevrolet S-10 Blazer four-door 4x4 with the 4.3L V-6. The engine was replaced at about 90,000 miles with a Jasper remanufactured unit. The engine has about 55,000 miles on it now. Ever since I got it back, I've had a starter problem. After it has warmed up from driving, and is left to set for about 5-10 minutes, the starter drags really bad. I've replaced the starter three times, each time from a different automotive supply place. The last time was from a very reputable place (NAPA). I've replaced the starter cable from the battery to the solenoid, as well as replaced the ground cable. I even installed the spacer that I received on the starter from NAPA, thinking that when it got warm, the starter would expand and be pushed further into the flywheel. That didn't help, either. I even replaced the battery.

I have taken the Blazer to two different repair locations and run tests on it, and no one can come up with a logical reason. One test said "battery bad" due to a high voltage drop, but when they test the battery by itself, the voltage is high enough that says the battery is OK. I had one guy say it was the starter, and tore it apart, put new bushings in it, checked the armature and fields, said it was fine, put it back together and it didn't help. I am fairly intelligent in most automotive problems, but this one has got me severely stumped. I would appreciate any help, suggestions, and/or ideas.
Donald Hessenflow
Independence, MO

Answer: First, we have to determine if the starter is actually dragging or if it is not getting full voltage. Find a shop that has an amp probe and a mechanic who knows how to use it. This is a high-dollar voltmeter that clamps onto the battery-to-starter cable and measures the amp draw of the starter.

If it is drawing more amps than the starter is rated at, then for some reason you have a drag. This drag could be induced from the starter getting hot or a misalignment. Let's take the heat issue first. Did you by chance change out the original exhaust manifolds for a set of headers, or perhaps just a new header pipe that is in a different location than the original? Could this be radiating heat into the starter? Chevy starters are readily noted for having starting problems from heat. Several places such as Summit Racing ( offer many different styles of starter heatshields.

Another solution is with a Starter Solenoid Kit. What you're doing is mounting a second solenoid on the firewall and running the battery cable to it first, and then down to the starter. You then run the wire that originally ran from the ignition key to the OE starter solenoid to this new solenoid, and add a special bypass wire on to the old solenoid. Now, when you turn the key, full amperage goes to the starter and none of it has to go through the ignition switch for starter engagement.

Now the problem could also be a major misalignment of the starter's teeth with the flywheel. You have to remove the dust cover to check this out. With the proper tool (a screwdriver usually works), move the starter's pinion gear into contact with the flywheel's teeth. The proper clearance between the teeth is somewhere between the thickness of a paperclip's wire thickness. You can buy a shim kit that has various thicknesses of shims that can be placed between the starter and the engine block under the mounting bolts. Their placement will depend on whether the starter's pinion gear needs to be moved closer or further away from the flywheel's teeth.

Question: I just read "Willie's Workbench" (Nov. '06) and I have some additional info on thick Dana 44 covers, since I have a '74 IH 100 1/2-ton and a '75 IH 200 3/4-ton pickups, as well as a '78 Scout II.

I bought two very thick (0.160-plus-inch at the flange) covers available from Complete Off Road ( This is one heavy-duty cover for $25. IH didn't make that many pickups, especially the '74-'75 models, and I hate to see the IH rigs unnecessarily scrapped just for its diff covers. The fill hole is about 1/2 inch higher than the diff covers that came on my Scout II. I didn't have a use for the tab that is spot-welded near the top so I ground it off. Duck soup!
Doug Shailor

Answer: Thanks for the info-I really appreciate help from readers, and it also tells me that some people actually read what I write ... well, at least once in a while.

Question: In response to your recent "Cherokee 2.8L Swap Options" question, I also have an '86 XJ with the 2.8L factory engine. I checked the Internet and found several articles on swapping in the 3.4L V-6 from a '93-'95 Camaro. It is dimensionally the same block. All the factory components can be bolted on; the only hurdles were modifying the flexplate and getting the carburetor adjusted.

Since the 2.8L is externally balanced and the 3.4L internally balanced, the 2.8L flexplate has to be modified and balanced. Since the Jeep uses a Chrysler 904 transmission, a Chevy flexplate cannot be used. I was able to drill/knock off the extra weight and drill some holes that brought my balance to neutral. I checked it on a wheel balancer.

The carb is a little different, as there weren't any aftermarket parts for the Varijet, so I just used a TBI intake from an S-10 along with all the electronics. The throttle body itself will need larger injectors (ideally from a 305), or you could swap in a throttle body from a 4.3L or 5.0L GM truck. The throttle bore is larger, so it takes some enlarging of the intake, but it works pretty good.

It is also possible to get a 3.4L directly from a GM dealer, and there was at least one company that offers kits to stroke the 2.8 to a 3.4. I added a Crane Cam and I now have decent power, room in my engine compartment, and reliable Chevy power. I also ended up adding a better radiator-the factory one-row unit couldn't keep up on the highway with 33s, even with 4.10:1 gears. I don't mind the 4.0L, but it is a big heavy engine that leaves little room in the bay of an XJ.
Lewis Nellinger

Answer: Thanks for the good word on the 3.4 swap. We always appreciate it when readers help us out on problems. You've covered the subject much better than we did. We like the ingenious way that you balanced the flexplate.

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