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30 Top Tech Questions

Posted in How To on June 1, 2012
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Contributors: JP Staff

Nobody knows it all. If you’ve got a Jeep, then you’ve probably asked several of these questions at one point in time. How are we so sure? ’Cause we’ve answered them a whole mess of times. Are we complaining? Heck no—everybody has to start somewhere. The more time we’re asked questions like these, the more new Jeepers are entering the fray. So, happily, here are the answers to the top 30 tech questions we’re asked on a daily basis.

Q My Jeep needs a new engine. What engine should I swap in its place?

A Again, here’s one of those loaded questions that really depends on what drivetrain your Jeep came with, whether you plan on retaining your factory transmission, and a host of other factors. But to play it simple, we’ll just look at only engines for a moment and the aftermarket support in place for each.

For starters, it’s hard to argue the cost, power, reliability, and ease of a small-block Chevy swap. Sorry Chevy haters, but they’re simply the cheapest and easiest. The small-block Chevy has been produced forever and you can’t hit any junkyard, swap meet, or online venue forum without tripping over oodles of good, usable candidates. The only downside to the traditional small-block is that most came from the factory with carburetors. However, nowadays you’re almost as likely to trip over a TBI (or even TPI or Vortec) 5.0L or 5.7L as you are an older carbureted version. And every aftermarket company in the world makes components to slam it, adapt it, wire it, and fire it in just about any chassis. Old-school carbureted small-blocks work well in everything from CJs to Willys wagons and trucks, FSJ pickups, Wagoneer, and Cherokees, and almost any other Jeep model.

Rapidly closing the gap in popularity are newer Gen III/Gen IV GM engines, including the 4.8L, 5.3L, 6.0L, and 6.2L truck engines, as well as the 5.7L, 6.0L, and 6.2L LS engines from the Camaro, Corvette, and other performance car lines. Sorry, but the 7.0L LS-7 and supercharged 6.2L LSA and LS-9 offerings are nowhere near affordable yet. However, you can often find a take-out 5.3L with harness and sometimes the electronic overdrive 4L65E transmission for anywhere between $500 and $1,000. The 6.0L, 6.2L, and aluminum LS engines fetch more, but offer more power and/or lighter weight. The 5.3L will put out between 285-315hp depending on year and model and will knock down some seriously impressive mileage numbers. The nice thing about the Gen III/Gen IV engines is they’re newer than many late-model Wrangler vehicles, which makes a smog-legal swap a possibility.

Finally, let’s not forget the smaller stuff for the vintage crowd. It’s hard to go wrong with a Chevy 3.8L/4.3L V-6 or a Buick 3.8L/231 even-fire/ 231 or 225 odd-fire V-6. The Chevy versions are nice because they accept standard Chevy motor mounts and bellhousings, while the Buicks have front-mounted distributors for firewall clearance in tight four-cylinder Willys engine bays.

Light on Speed
Q I just got finished installing some flush-mount LED taillights and now my turn signal blinks way too fast. Did I break something or install them incorrectly?

A You didn’t break anything, and odds are really good that since a fuse didn’t pop, you’ve installed the lights correctly. What you are seeing is actually a “built-in” feature of your Jeep and many other automobiles. Most people don’t walk around the vehicle inspecting to ensure their lights are all working correctly, so it was decided to add this feature to alert a driver that a bulb is out on the vehicle. On the road, if you see a blinker on one end of the vehicle blinking faster than it should, the corresponding light on the other end will be out. It is called the “black out bulb” feature (BOB for short).

Fortunately, BOB is a part of your flasher module which, as we all know, is easy to swap out or change. We won’t get into the change of load on electromagnetic function here. We also won’t bore you with the way we used to open up flasher modules and cut trace wires on circuit boards or solder tiny relays onto them. Today, fixing your fast-flashing Jeep is as easy as going to your local parts store and getting a new flasher. Due to the proliferation of LED lights into the marketplace, most flashers no longer have a BOB function. Just look for the “LED” printed on the end of the flasher as shown in the picture and swap your old one out.

Cold and Crispy
Q I have heard that in my TJ if I run the heater on the highest setting it can cause a fire. Is that true? How do I avoid burning my Jeep? I’d like to be warm again in the winter—but not that warm!

A While we haven’t actually seen a Jeep catch fire from HVAC wiring, we have seen smoke coming out of the dash of a few of them.

The root cause is wear in the blower motor. As the motor wears, it draws more amperage. As it draws more amperage, the wiring in the dash heats up trying to pass more current than it was designed for. It’s a brutal cycle that keeps feeding on itself until your speed resistor dies, your wiring and/or switch in the dash melts and falls apart, or the blower motor just stops working. In the past, we have wired relays into the system only to see them melt again.

In “Jeep Fire Prevention,” (Oct. ’07), we put a series of relays in the system to take the heat out of the switch. We measured the temp of the switch before the modifications at 122 degrees, and you can see how we fixed it here: prevention/index.html

Then, in “Safe Heat,” (May ’12), we had to do it again, since the original fix only lasted for that amount of time, eventually melting another switch irreparably. By then, we’d learned more about the problem and how to fix it.

High Lock
Q I have a Rubicon and the lockers are great, but low range is no good for mud or sand. Can I modify my Jeep so that I can engage the lockers anytime I want to and not just in low range?

A Yes, it is totally doable. On a TJ, first pull the center stack in your dash off and gain access to the rear of the locker switches. Then, for the ’03 and ’04 Rubicon, ground the red wire with the white stripe. For the ’05 and ’06 models, you need to ground the violet wire with the orange stripe. Grounding the wires fools the switch into thinking the Jeep is in low range. If you have an ’07-or-up Wrangler Rubicon it is possible to fool the computer into thinking it is in low range, but you have to start jumping wires between pins on the computer. The exact procedure can vary depending on what year your Jeep is, and we simply don’t have the space here to cover it all. Beyond that, if you screw something up, it is likely damage to one or more computers in your JK will probably be the result. And, if that wasn’t enough, the Jeep most likely will realize at 18 mph that you aren’t in low range and trip a code that your dealer can see (which might affect your warranty). The safe way to do it is to pick up an aftermarket tuner that offers this function.

Q I am thinking of getting an XJ, but my friends warn me away from the ’87 to ’90 models with the 4.0L, telling me that the fuel-injection system is weird and has a lot of inherent problems. The chance of fire and cooling problems are but a few of the things I am worried about.

A The years you are talking about do have a different injection system than the later ’91-up 4.0L HO engines. The early system is called “Renix” injection. It was designed in conjunction with Renault and brought Jeep out of the computer-controlled carbureted nightmare. Because Renix came on the scene relatively early, it doesn’t even adhere to OBDI diagnostic protocols and can require a special scan tool to accurately diagnose certain problems. That said, when they are running well, they are as reliable as the Chrysler MPI system of the later 4.0L HO engines.

The cooling problem you are hearing about is another one of those things a lot of people are needlessly scared of. It is often referred to as a “closed” system because the coolant overflow tank is closed off from the atmosphere. Again, if your system is working, it will cool the Jeep just as well as the “open” system that came later. There are two little caveats that give it that bad reputation. The first is that the overflow tank mounted on the passenger side firewall is pressurized. It is made of plastic, and over time both the plastic cap and the plastic tank can become brittle, leak, or just stop holding pressure. When that happens, the system can boil over the same as releasing the pressure of a regular cooling system. You can go scrounging junkyards for usable tanks, but the most recent one of these Jeeps were made over two decades ago and we’ve not had much luck finding them in junkyards. Today, however, a quick Google shopping search will find you a lot of new plastic ones with little effort and for little cash. Or, if you want a more permanent solution, Macs Radiator Shop ( offers aluminum tanks for just a bit more coin. If the radiator is still good, the replacement overflow is a good route to go. The second reason the closed system gets a bad rap is that it can be difficult to get all the air out of the system. To get the air out of a closed system when filling, park the Jeep nose-down, remove the coolant temp sensor on the back of the head, and start filling the overflow. When coolant comes out the sensor hole, replace the sensor, and continue filling to the full line.

We prefer the open system because any overflow tank will work and there are more high-performance aftermarket all-metal radiators for the later system.

As for the fire issue, we’ve lived it first hand and only afterwards did we learn of the possible issue. The injectors are known to leak. They can leak both past the O-rings and from the injector body itself. The fix can be seen here:

How do you tell if your Jeep is in imminent danger of burning? Well, for us, at the time, we knew we had a problem, but couldn’t find the source. The Jeep would sporadically lose power at first. Then we noticed that when we lost power we’d smell gas, but couldn’t find the source. Looking back now, of course it is obvious.

Q How do I make my speedometer accurate again after bigger tires or gear change?

A We see this question quite a bit. The short answer is that you either need to change the drive gear in the T-case, or you need to do it electronically. Generally speaking if your Jeep is a ’91 or older, you need to swap speedometer drive gears. If your Jeep is an OBDI-injected vehicle from ’92-’95, or ’96-’06 and OBDII, you can use either speedometer drive gear swaps (if your Jeep has one) or electronic programmers. Once you get to the newer Jeeps that no longer have either speedometer drive gears or tone rings in the T-case but rather read wheel speed at the wheels, an electronic tuner is going to be your only choice.

Q I’m thinking about buying a Jeep XJ/MJ, but all the best ones I find are 2WD. I want a 4WD Jeep. How hard is it to convert it to 4WD? How do I convert it over to what I want?

A This question can be such a can of worms because there is no one right way to go about it. There are so many parts required to do it, and so many out there that will get the job done the sheer number of permutations are staggering. But the flip side of the coin is that despite all the components you will need to swap out, it isn’t a difficult thing to do. It will be easier if you are converting a Cherokee, but by no means impossible to convert a Comanche to 4WD, either.

You can use a factory front axle from a TJ, XJ, MJ, or ZJ. They will all bolt right in. There are pros and cons to all of them, though. You can swap the mainshaft and tailshaft on your existing transmission, you can nab a used 4WD transmission out of another Jeep, or you can get a new transmission from numerous parts warehouses. As for the transfer case, it’s entirely up to you what to use. You can go aftermarket with something like an Atlas II and use Advance Adapters’ ( linkage. Or go with a new factory-replacement ’case and use Advance Adapters’ cable shifter setup. With all of that said, the easiest, cheapest, and most fool-proof way is to pull used parts out of the same year vehicle in the junkyard. The reason we say fool-proof is because, depending on the year, you could see input spline changes and speedometer sender changes that you might not notice until you are under the Jeep putting it together. For more information, check out the story where we converted a ’91 Comanche Eliminator to 4WD in “2WD to 4WD With Junkyard Parts,” (Sept. ’11).

Gauge Alive
Q Can I keep my factory gauges after I do an LS-based engine swap? The engine swap itself costs enough; I’d like to save some money by keeping the factory gauges.

A Until recently, this would have been a much more complicated answer. Older Jeeps use dedicated sending units for the gauges (’95-and-earlier), but most OBDII Jeeps on the other hand use data sent from the computer to run the gauges. If that wasn’t enough, there are two distinct OBDII systems. Of course, “OBD” stands for “On Board Diagnostics” and vehicles with this system carry a lot of information back and forth to the computer so it can run the engine, automatic transmission, ABS, and more. The early OBDI systems barely carried enough information for the computer to run the engine. Computers in vehicles were underpowered and slow, so they kept it simple. As engineers got more experience and better hardware they moved to the OBDII, which carried more information and allowed for finer tuning and better diagnostics. Then we moved up to a CAN bus-based OBDII system and even more information was sent back-and-forth. “CAN” of course means “Controller Area Network.” Early OBDII Jeeps (such as the early TJ and late Cherokee) had some sensors that drove the gauges directly, and some that were passed through the computer.

Why do you care about all that? Well it is really background for this: If you put a CAN bus-controlled engine in your Jeep, up until now you would have had to put all new aftermarket gauges in it, along with dedicated sending units; this not only raises the overall price of the swap, it can also create more underhood wiring than needed. And, some later-model engines just don’t have enough ports for all the sensors you might need. Painless Performance Wiring took a look at the problem and realized that the CAN bus system already carried the information needed for the gauges that most of us want to run. The company then developed a gauge controller that can not only take the CAN bus signal and turn it into something an aftermarket gauge can use, but it can also use a CAN bus signal to drive your factory gauges. As of press time, the company is still working out compatibility for early OBDII Jeeps. However, they tell us that for any factory CAN bus-inflicted Jeep, or for OBDI Jeeps (’95-and-earlier), the system will work. As of press time, the system is being developed for ’07-and-up GM-sourced V-8 swaps into other vehicles.

Battery x 2
Q Do I really need dual batteries? A lot of the guys in my club who have been around a while are running two batteries in their Jeeps and swear by them.

A No. Seriously though, if you have to ask, most likely you don’t need to go through the expense, weight, and time of putting in dual batteries. Don’t get us wrong, there are guys out there for whom dual batteries are a necessity. But if you’ve not done anything that kills your primary starting battery, or even come close to it, then you probably aren’t one of those guys.

Do a lot of engine-off winching? A lot of high-load, engine-on winching? Listen to stereo or run lights in camp and can’t start the Jeep at the end of the weekend? Have an insane aversion to carrying jumper cables? Have a busted-down or high-compression engine that doesn’t like cranking over in the cold or extreme heat and you don’t want to swap it out? Like camping in 110-degree desert heat for a week with a DC-powered fridge but can’t or don’t want to run the Jeep twice a day for an hour at a clip to keep your starting battery charged? Then yeah, you might need dual batteries. We don’t hate the mod, we’ve even got a couple of projects running dual battery setups. But we hate when people tell others they “need” something. Usually if you need something you know it, and dual batteries are definitely in that category.

Q My older Jeep was having some weird electrical issues and I chased it down to a loose fuse in the fuse block. It looks like the previous owner had something stuck in there. Is there any way to fix it?

A Well, without knowing what year/make/model of Jeep we are talking here, we’ll give some general advice. First, as much as we make fun of instructions that tell you to remove the negative battery cable before starting, you’re going to want to do that now. For safety, you always want to disconnect the battery before playing around in the fuse block. Once you are done with that, sometimes it is possible to tighten up loose fuses by first removing the fuse and then gently (we are talking to you, Magilla) prying on the connector with a small flat-blade screwdriver can tighten it up. That will usually solve the problem. If it doesn’t, it is possible to pull the fuse block off the firewall, de-pin it (that is, remove the offending connector), and go from there.

Usually a loose fuse is caused by someone just jamming a wire into the fuse block to wire something up. This is to be avoided. The connector shown in the picture can be used for wiring things up by piggy-backing on an existing fuse, if you don’t have an accessory location available. They can be found at your local parts store. We have also used them to fix the loose fuse problem as well. It isn’t the correct way to do it, but it sure is a lot faster and easier than pulling the fuse block apart. And if you are adding a circuit, you can kill two birds with one stone. If you aren’t adding a circuit, you should tape the end that protrudes past the fuse to avoid short circuits. If the original owner had added an auxiliary fuse block from the beginning, you wouldn’t have this problem now. If you know you are going to be adding more than one circuit, you can use Painless Performance’s auxiliary fuse block like Randy did in “Randy’s Electrical Corner: Start Off Right,” (May, ’08):

To E-fan or Not To E-fan?
Q Is an electric fan worth it? What are the advantages of an aftermarket electric fan versus junkyard?

A Whether an electric fan is worth it or not is going come down to what your needs are and how you use your Jeep. If your Jeep sees water crossings frequently, then an electric fan is always a good idea. When idling or crawling, an electric fan will generally flow more air than a mechanical fan can, so if you are seeing overheating problems when going slow on the trail, switching to an electric might cure it. If you live where it gets cold in the winter, leaving an electric fan off will help the Jeep warm up quicker.

Aftermarket electric fans and the junkyard route both have their pros and cons. Especially if you’ve got a Wrangler or CJ, the aftermarket has literally hundreds of offerings that will bolt right into your Jeep, regardless of what engine you might have in it. Flex-A-Lite’s ( Black Magic Extreme 485 will bolt into any ’87 to ’06 Wrangler using the factory radiator mount holes and includes a fan controller with detailed instructions and connectors. It is a one-stop solution that is hard to beat. Got an XJ or MJ? In addition to a kit for Wranglers, FFDynamics ( has a killer three-fan setup that fits the goofy-sized XJ/MJ 4.0L radiator.

However, if you are on more of a Ramen Noodle budget, there are thousands of cars sitting in a junkyard today with a fan that might work for you. You can usually get one for under $30, but then you are on your own to figure out how to mount it, wire it, and generally get it working. At the very least, you will need to fabricate brackets to get the fan attached to your Jeep, and might have to go as far as building an entire fan shroud. Once you figure out how to get the fan in your Jeep, then you need to figure out how to wire it up and source not only the switch and relay, but all the wire and electrical connectors. The dual-speed Ford Taurus fan can flow a ton of air, but there can be issues with reliably feeding it enough power to turn on because it pulls a lot of amperage at start-up. The junkyard route is best left alone if you aren’t skilled at building things or if wiring scares you.

Speaking of wiring, you can go from as simple as a switch and relay, to an automatic underhood fan controller, to a PWM controller. A “normal” controller will turn the fan on at a set temperature and off at another temperature. A PWM (Pulse Width Modulation) controller has the capability to vary a fan’s speed across a range of temperature. Think of it like your A/C knob on your dash without detents. The hotter you get, the faster you make that fan go. Because of the ability to vary the fan speed, there is less current used and less wear-and-tear on the fan itself. A PWM controller also solves the problem of the Taurus fan by starting it slow. SPAL USA ( currently offers a PWM controller (PN FAN-PWM), but they tell us that they are phasing it out. Fortunately, by the time it is phased out, Painless Performance Wiring should have their new PWM controller on the market.

Speedo Freak
Q So I noticed that my speedo is off after a gear and/or tire change. Why did that happen?

A First, for the love of dog, please tell us that you are talking about your speedometer and not your bathing suit! It turns out that if you increase tire size by 10 percent, then your speedometer will read 10 percent slower as you buzz down the highway. Likewise, if you lower your gear ratio by 5 percent, then your speedometer will read 5 percent fast. Here are a few formulas that will help you figure out how fast you are really going so that when the cop pulls you over you can explain your behavior. You should probably be wearing more than a speedo when you get pulled over. Just sayin’.

Speed from your tachometer:

(rpm x tire diameter)

mph = ____________________

(gear ratio x 366)

The tire diameter is important here, and it does not necessarily mean your sidewall specifications. Actual tire diameter is often shorter than what’s written on the sidewall. Use a tape measure to get the actual diameter.

Here is an example of if you were to swap from stock 27-inch tires to 33-inch tires (actually about 32 inches tall). So 32-27= 5 inches, and 5/27=.185, so the 33s are about 18-20 percent larger than your original tires. This means that if your speedometer was fairly accurate before you added bigger tires, then your speedometer will now read about 18-20 percent slower. So in order to know your actual speed you would have to subtract 18-20 percent of your indicated speed.

You can also use your incorrect speedometer reading and this formula to get your actual speed. Again, this tire size means actual tire size, not claimed tire size:

new tire size x

(indicated speed)

actual speed = _________________

old tire size

Oops! I Slipped on the Yoke
Q I am thinking of lifting my Jeep. When do I need a slip-yoke eliminator and should do a hack-and-tap or heavy-duty 32-spline replacement shaft?

A The design of having a slip-yoke integrated into the back of the transmission or T-case is fine for cars or stock height Jeeps. As soon as you lift a Jeep the driveshaft is at more of an angle relative to this slip-yoke and as a result tends to push up more on the rear of the factory transfer case. This increases bearing wear and shortens T-case lifespan. Eventually this leads to worn bearings, leaky seals, and may end in a tailshaft housing failure.

Losing the slip yoke shortens the T-case, lengthens the driveshaft, and lessens the U-joint angularity to mitigate vibration. This is further enhanced by the use of a double-cardan driveshaft that requires the pinion to be moved up again lessening the angles of the driveline. As for heavy-duty 32-spline verses hack-and-tap slip-yoke eliminators, it should come as no surprise that we think you should pony up for the stronger, better engineered, and yes, more expensive heavy-duty parts. This is because you are modifying your vehicle to work better off-road, right? You want it to be more reliable and not less reliable. The idea of installing a hack-and-tap slip yoke eliminator in a driveway is honestly frightening to us. Basically you are choosing to reduce the amount of spline engagement to the rear yoke by trying to cut, drill, and tap the very center of a hardened metal shaft that will have huge forces traveling through it.

There is no real formula or amount of lift that clearly dictates when you will need a slip-yoke eliminator, but generally any Jeep that has over 3 inches of lift would probably benefit from one and the longer double-cardan rear driveshaft that usually accompanies it. The truth is we know that some stock-height Wranglers could use a slip-yoke eliminator and we have heard of longer wheelbased Jeeps like XJs, ZJs, and WJs that are basically fine retaining the stock slip yoke despite a 4-inch lift. Also, T-case lowering kits can help reduce vibrations to an acceptable level, although some may consider lowering part of your drivetrain to be counterproductive.

Boat Anchor!
Q My Jeep has a Dana 35 rear axle. Should I upgrade my Dana 35 or swap in another axle? If so, what axle?

A Sell it! Unless you are planning on leaving your Jeep totally stock and wheeling it mildly with 31- or 32-inch tires and no rear locker, your Dana 35 will prove to be a money pit. By the time you’re done bolstering a Dana 35 with better 30-spline axleshafts, new gears, a locker, and a housing truss, you’ll be nearly at the price of an aftermarket axle assembly.

If you want to put a real axle in your Jeep there are several options. Viable and common junkyard donor rear axles are; ’90s 4WD Honda Passport and/or Isuzu Rodeo Dana 44; a centered rear Dana 44 from an full-size Jeep with new six-lug wheels and some five-lug to six-lug adapters for the front axle; ’90s Ford Explorer 8.8; and ’97-up XJ Chrysler 8.25. Slightly less common, but equally good junkyard swap candidates are ’87-’89 Jeep XJ/MJ Dana 44 and V-6 2WD (non-Prerunner) Toyota Tacoma axles. You may also be able to find a TJ/LJ/Rubicon rear Dana 44 or a JK Dana 44 in a specialty junkyard or on craigslist or eBay for a reasonable price.

Boat Anchor?
Q Why is or isn’t a Ford 8.8 a good swap?

A Many of you Ford 8.8 lovers out there think we hate the Ford 8.8. Not so. We simply feel it’s not the only option. There are several good junkyard axle swap candidates out there that can be done for less cash than the Ford 8.8. Consider that if you buy one in the junkyard for $95-$120 with 4.10:1 gears (and that’s the ratio you are running), you may be getting a good deal. Unfortunately, lots of places are hip to the popularity of the Ford 8.8 Jeep swaps and are charging more for these axles. Also, the Ford 8.8 is really not that inexpensive once you add in the cost of wheel spacers (the Ford 8.8 out of an Explorer is about 3 inches narrower than the stock Jeep axle); costs of a re-gear (most have 3.73 gears); weak stock carriers (so you might as well add a full-case locker); some have 28-spline axles (watch out); brackets to get the axle under your rig (OK, this is something you will need for most axle swaps); a thicker rear diff cover (the factory covers are very thin); and a 1310-to-Ford flange adapter. You are quickly approaching the cost of a much stronger and lighter custom-built Ford 9-inch with chromoly shafts. The fact is that you are not going to go to the junkyard and plop down $250 for an axle from a Ford grocery-getter that is going to fit directly in to the back of your Jeep, it’s gonna have to be customized to fit and will probably end up costing more like $1,500-$2,000.

If you are really going for a bottom-dollar axle upgrade, pulling an Isuzu/Honda rear Dana 44 with factory 4.56 gears and a limited-slip differential would be a better swap. Or, how about a Toyota 4WD axle with factory 4.56s and a Lock-Right? Sure, the bolt pattern of either of these axles is incorrect, but the add-in the cost of some used 15x8 six-lug wheels and the cost of wheel adapters to go from 5-on-41⁄2 to 6-on-51⁄2 for the front axle. That’s gonna cost about the same as upgrading your factory five-lug wheels and the cost of the 11⁄2-inch wheel spacers you’d have to buy for the Ford 8.8. Yeah, they are fairly strong and fairly plentiful, but there are other rear-axle-shaped fish in the sea!

Four-to-One for Me?
Q I have a Jeep and one of my buddies read about a 4:1 transfer case conversion. He is totally convinced that this is what I need. Should I do it or keep my standard T-case ratio?

A The answer is you should probably not put a 4:1 T-case in your rig. Unless you have a four-cylinder or all you do is dry rockcrawling, a 4:1 gearset in your transfer case is probably going to be too low for most of your wheeling. Get in the sand, mud, or muddy rocks and you will probably want more wheelspeed than 4:1 will allow. Also, one problem with a 4:1 kit installed in the common Jeep NP231J is that if you couple it with a heavy-duty slip-yoke eliminator, you will be very close to spending as much or more than the cost of a new Atlas II on a weaker, used T-case. Your money is better spent on an Atlas II.

Now, if you have an older Jeep with a Dana 300, Dana 20, or Dana 18 and you either have a four-cylinder and mainly do rockcrawling, a low-range gearset in your T-case may be the way to go, but be ready to lose the option of wheel-speed. Why so much about four-cylinders? Well if you have one you know you probably won’t be shooting any dunes or slinging lots of mud anytime soon, so gearing may be your best and only option to get further down the trail. Lastly low gearsets generally increase the load on a T-case. That’s because the torque and power running through the T-case is now multiplied nearly two-fold. This means that if your 60-year-old T-case housing is damaged it will probably fail right after installing these gears. Some gearsets also require grinding to the case, further weakening them, and it’s debatable if the cast aluminum of a NP231 is up to the added strain of the lower gearing even when brand new. If your Jeep has the historically very strong Dana 300 and a relatively high first gear (we are thinking T-14, T-15, and T-176 to name a few) a 4:1 may be cheaper and easier than swapping your tranny out for one with a lower First gear.

Locker for You, Locker for Me
Q Hey ya’ll, what should I run in my Jeep? An automatic locker, selectable locker, or limited slip?

A Well the truth is we need to know more about what you are doing with your Jeep, how it’s built, and how it’s used to tell you that. It’s hard to beat a tight limited slip for on-road performance come snow, sleet, or rain. Also, a limited slip works great for high-speed off-road (desert race) driving and they do pretty well in mud. Hell, a limited slip is pretty sweet on mild off-road trails too, but as soon as you get to a point where a tire is lifting completely off the ground, a limited slip is almost as frustrating as an open differential.

If you are going to put your Jeep in this kind of situation frequently, you may want a true locking differential. Probably the most famous and reliable automatic locker is the full-case Detroit Locker. Detroits offer phenomenal traction off-road, but are known for quirky on-road behavior, especially in short-wheel based Jeeps. If you have a short-wheel based rig and drive it in snow, a Detroit can be downright scary. If you are coming around a corner on snow or ice and the Detroit locks or unlocks, you may find yourself in a ditch.

Manual (aka, selectable) lockers are a little more forgiving on road because you can turn them on or off depending on where you are driving your Jeep. On-road the locker is off, providing regular open-differential behavior, or limited slip action and drivability. However, when engaged off-road you have the ultimate in spool-like traction. Both wheels are going to turn. Sounds perfect, right? Well, not quite. Selectable lockers are relatively expensive and if they fail, they generally fail to unlock … that’s good if you are driving to the store, not so much if you are in the middle of gnarly trail.

The last option is a full spool. A full-case spool offers the ultimate in traction and the best part is they are relatively cheap and stupid-strong. The downside is on the road a spool will cause your tires to chirp and scrub. A spool, like an auto locker, would also be somewhat frightening in slick conditions. Expect taking corners like Ken Block in rain, snow, or ice!

Spinning Discs
Q How do I go from drum to disc on my Dana 25/27/44?

A Upgrading to disc brakes on the front of an early Jeep with a closed-knuckle axle is a fairly simple recipe The ingredients are available at junkyards all over the country. Basically you will need Chevy 1⁄2-ton caliper mounting brackets from a Dana 44 or GM Corporate 10-bolt front axle (’73-’91 K-10, Blazer, or 1⁄2-ton Suburban) or Jeep FSJ Dana 44 front axle; Chevy or FSJ calipers; pads; brake lines; mounting hardware; and ’77-’78 11⁄8-inch-thick CJ rotors. You will re use your hubs, spindles, locking hubs, and mount the CJ rotors to the stock hubs with ’77-’86 CJ wheel studs. Also the closed knuckle will need to be ground down in certain areas to allow the caliper to move freely as your brakes work and pads wear. You may also need to machine certain areas of your knuckles depending on which axle you are working on. Remove the residual-pressure check valve from any dual-pot master cylinder. To do this, use a machine screw to remove the brass fitting from the front brake output port (usually in the back). Thread it in and pull out the brass fitting. Remove the rubber check valve and spring and reinsert the brass fitting minus the machine screw.

For specific outlines of how we have done this swap on an FSJ Dana 44 and Dana 25, respectively, including part numbers, check out “Closed Knuckle Upgrades,” (May ’11).

Reversal of Fortune…er, Motion

Q Hey Jp, is a shackle reversal worth it? Are there any handling drawbacks?

A In a shackle-reversal front suspension, the spring shackles are mounted behind the front tires. In this arrangement, as the suspension compresses and the spring flattens, the axle actually moves up and slightly backwards, which is how it naturally wants to move as you hit a bump at speed. In a standard Jeep shackle-forward arrangement, the axle will move up and slightly forward, making the bump seem more jarring.

Shackle reversals generally offer a smoother, more predictable ride, but some argue this natural up-and-back motion isn’t as good off-road for climbing obstacles. In cases like that, you want the tire to get forced into the obstacle as you are climbing it, which is what happens in a Jeep with positively arched springs without shackle reversal. To add to the complication and misunderstanding of choosing shackle reversal or not, flat, or negatively arched springs, behave differently than positively arched springs as they flex. If you have a flat or negatively arched spring (as in a spring over) then the axle may move in the opposite direction relative to the frame than a highly arched spring would with the same shackle set up (front or rear). So is shackle reversal worth it? Again it depends on what you are doing with the Jeep. We’d say that if you have a CJ or YJ with highly arched lift springs and want to go fast off-road or ride quality is important to you, it’s a good idea.

Lifting the Pentastar
Q I have a ’12 JK and I want a lift kit. I am told that the exhaust manifold on the new engine requires modification for a lift to be installed because of the loop-de-loop on one side. Then I was told that Jeep doesn’t recommend any change to the exhaust manifold because the new engine requires the stock exhaust to run correctly. What can I do and is there a company that makes a lift kit that doesn’t require me to alter the exhaust manifold?

A As we are writing this, we can promise you that every aftermarket suspension company that makes a lift for the ’12-up JK has been addressing this issue. But let’s talk about what that loop-de-loop, snail curl, or doughnut does. It equalizes the length of the left and right pre-cat exhaust tubes. The equal-length exhaust maximizes scavenging within each cylinder, thus allowing the Jeep engineers to reach the 3.6L’s impressive 260 lb-ft, table-flat torque curve. So, removing the loop actually compromises the efficiency of this high-tech engine. Although some kits have already come to market that replace the loop with a shorter, unequal-length tube, we recommend that you keep equal-length tubes on your Pentastar. You can do this by either by running an equal length aftermarket down pipe or some suspension companies recommend and produce a drop exhaust extension that works with your stock pre-cat exhaust.

There are also some issues with the portion of the exhaust that runs under the front driveshaft on these Jeeps. Also, the engine and drivetrain on the ’12 JKs is mounted at a higher angle relative to the frame, which complicates driveshaft angles up front. One fairly innovative option that helps deal with both of these issues involves a very narrow U-jointed front driveshaft from J.E. Reel ( This new shaft allows more movement before the body will hit the exhaust. The driveshaft is also serviceable (while the factory is not) and uses 1310 U-joints that allow the driveshaft to spin at higher angles without binding.

Boom! Death Wobble Dead, Sucka!
Q I have experienced death wobble and lived. Now how do I diagnose and cure death wobble?

A If it’s happened to you, you know it. It usually happens at a certain speed, as you begin a turn at a certain speed, or if you hit a bump or pothole. When it happens the wheel starts jerking back and forth and the whole Jeep shakes till you can slow down—the aptly named death wobble. It sucks. So what causes it, how do you diagnose what is causing it, and how do you fix it? Well it’s usually a combination of problems adding together to make a very noticeable symptom. Tires out of balance, warn, or damaged steering or suspension parts, too much or not enough toe in, mud on the wheels or usually a combination of these cause death wobble. Curing death wobble can be one of the most frustrating undertakings. Just to be clear, generally a steering stabilizer, two, or three is just a Band Aid that temporarily covers up the problem, but won’t fix it. If you have big or excessively worn and chunked tires, or even a little mud on the wheels, that may be contributing to or causing your death wobble. Get the tires balanced and or wash off the mud. Put the two tires with the least wheel weights up front, or if you are too cheap to get the tires balanced just swap tires front to rear to see if that helps. The rear of your Jeep is less susceptible to side effects of out of balance tires.

If you still have death wobble, and you probably will, here is how to figure out what’s wrong. First get a friend to turn the steering wheel back and forth while the Jeep is parked and you can pop your head down and look at the front steering and suspension. If you hear any popping (you also probably hear this popping as you are driving around the corner) or if you see any excessive movement you have a problem. Usually the track bar will pop if loose or worn out. Sometimes tie-rod ends will pop when worn. Replace or repair as necessary. If there is excessive movement without popping you may have worn control arm bushings or bad tie rods. Next jack up the front of your Jeep. While in the air grab a tire at 12 o’clock and 6 o’clock, alternate pulling the top and pushing the bottom with pushing the top and pulling the bottom. If the tire wobbles in and out then you probably need new ball joints. Now grab the tire at 3 o’clock and 9 o’clock and repeat. If there is any slop here, you probably need new tie-rod ends. Your steering box or shaft may also be loose or worn. Also check for cracks around the steering box mounts and make sure the bolts holding the box in place are tight and torqued to specification. Lastly, check to make sure none of your steering components are bent, as this can cause or contribute to death wobble. We have noticed that on some heavily wheeled or high mileage TJs rust around the frame-side track bar mount where it touches the frame can be a giveaway that the mount itself is loose.

Which Winch
Q Should I run a cheap Chinese winch or go for a more expensive model? Or, how about an older used Warn or Ramsey?

A We feel kinda naked if we don’t have a winch on our Jeep. A winch does way more than just get you unstuck if you high-center or can’t climb an obstacle. They can be used to straighten bent steering or suspension components, right a rolled vehicle, load your Jeep on a trailer if its engine dies, do yard work, or even just complete the look. In those regards, any winch is better than no winch at all. And in these hard economic times we can understand the appeal of an inexpensive winch that promises decent performance. In truth, the quality of many China-built winches is actually on the rise. It sucks, but it’s true.

So which do we recommend? If you can afford it, we still recommend going with a top-shelf winch like those manufactured by Warn. The company broaches its own gears right here in the U.S.A. and keeps tight tabs on quality control to ensure the soldering, solenoids, clutch, brake, and other internal systems can take a pounding without coming apart. A good Warn winch will last the life of your Jeep, if not longer. We’ve also had very good luck with Ramsey winches, although the remote connector pins can sometimes get a bit fussy. Conversely, some of the Chinese-built winches we’ve run have suffered solenoid failures during the initial cable spooling operation, not to mention broken teeth, fried solenoid packs, and other issues that would leave you without a winch when you need it most.

With regard to buying used, it’s not widely publicized, but Warn, Ramsey, and many other manufacturers stock replacement parts for a surprising number of old winch models. Often, if you are handy you can make an older winch work like new again with some disassembly, cleaning, and perhaps a few new replacement parts. So, if you’re somewhat comfortable behind a wrench, an older used top-shelf winch can give you reliable performance as well as serve as a cool conversation piece.

Finally, if you’re inept with hand tools and/or just plain broke, go China. Like we said, running an import winch is better than running no winch at all and the quality is most definitely adequate.

AL or FE?
Q I’m about to buy body armor for my Jeep and need to know if I should go with heavier, cheaper steel or do lighter, more expensive aluminum?

A When selecting armor, it largely comes down to how you use your Jeep. If you’re out on the trails dragging your Jeep’s vital bits on rocks like a slab of cheese over a grater, then the choice is obvious: steel. If you never, ever take your Jeep in rocks but want protection for dirt berms, sand hills, and other soft trail obstacles, then the choice is equally obvious: aluminum. But in reality it’s not that cut and dry and often the true solution is a combination of both.

The big advantage to aluminum is weight. On average, aluminum armor is about 1⁄3-1⁄2 the weight of its steel counterpart. For a Wrangler armor package (rocker guards, front and rear bumpers, and front tube fenders) that can add up to about 140 lbs, which is enough to make a notable difference in how the vehicle accelerates on road and reacts off road. The disadvantages of aluminum are three-fold.

First, it doesn’t have the brutal strength of steel in terms of abrasion resistance. Aluminum is much softer and will scratch and gall easier. This lets the rocks really take purchase on the aluminum, lending to an increased feeling of “stickiness” since the softer aluminum armor won’t glide over rocks like steel. Second, it’s harder to properly manufacture. Companies well-versed in building steel armor often hit roadblocks in aluminum armor since aluminum tubing reacts differently when bent, aluminum sheet can splinter and wrinkle if not done properly, and it takes a higher degree of skill to properly (and aesthetically) weld. Finally, aluminum armor is generally 40 to 45 percent more expensive than its steel counterpart.

As we said, the true solution to most Jeeps is to mix-and-match aluminum and steel. For a vehicle that will see only mild trail work, we’d be inclined to do aluminum corner guards, rockers, tube fenders, and perhaps even front and rear bumpers with steel undercarriage skid plates. On a Jeep that would be used more-heavily off-road in rocks, we’d substitute steel for the rockers, bumpers, and perhaps the front tube fenders.

Q What’s better: spring-over or spring-under?

A It’s all about the leverage, man. The tire’s contact patch on the ground is the handle and the spring-to-axle pad is the fulcrum. In a spring-over suspension, the lever between the contact patch and spring perch is longer, so there’s more leverage imparted when power is applied. This extra leverage overwhelms the spring pack, causing it to go slightly S-shaped and allowing the pinion to wrap upwards. In severe cases with light, flat spring packs, it can be enough to snap driveshaft U-joints or smoke pinion yokes.

In a spring-under suspension, the lever is effectively 4 to 6 inches shorter, so there’s less rotational force imparted to the springs and axle. The downside to the spring-under is that you have to run a more highly arched spring pack, which can limit flex in poorly constructed leafs. Also, the entire spring, U-bolts, and U-bolt plate are located down low in the way of trail obstacles. On the plus side, spring technology has come a long way and the aftermarket has done a relatively good job of creating an arched spring pack that still remains flexible. And there are many high-clearance and/or U-bolt flip systems available to minimize parts hanging down low.

On the spring-over side of things, you can generally run a flatter spring, which has the increased ability of offering equal amounts of up- and downtravel as compared with a highly arched spring. Furthermore, the spring-over setup can often utilize stock leaf packs from a variety of donors to avoid the expense of aftermarket springs. That said, it’s often necessary to run a flex-limiting traction bar of some sort in the rear and expensive, complicated high-steer or crossover-steering components in the front.

What’s better? A good, old-fashioned spring-under suspension system that bolts in place of your factory springs will serve the majority of Jeep owners very well while offering decent flex and superb resistance to axelwrap or axle dive.

Unrealism X4
Q How do I get 1,000hp out of my 2.5L?

A Listen now and hear us later. There’s really no economical way of increasing your Jeep’s 2.5L output more than 5 to10 percent. It sounds good until you realize that equates to only 7 to 15hp. Generally, modifications like a cold-air intake, free-flowing exhaust, larger throttle body, and an electric fan will get to that 5- to 10-percent bump, but going for more will only find you wasting money.

Sure, you can consider superchargers or turbo systems to get 4.0L power out of your four-cylinder. But then you’re just going to blow up a transmission that’s only marginally acceptable at your stock four-cylinder’s power level. Our advice is, rather than spending thousands on a turbo or supercharger kit for these engines, spend $1,000 or so to toss in the steepest axle gears you can. We’ve found 4.88s work well with 31s or 32s; 5.13s are good for 33s-35s, or 5.38s are good for 35s-37s. But since 4.88 is the best you can do in the stock Dana 35 rear, you’re stuck swapping axles—which is more money. Welcome to the Jeep sickness!

Stroker Smoker
Q Is a stroker 4.0L worth it?

A A standard 258ci six-cylinder has a bore and stroke of 3.750x3.895 inches. They made great torque, but less than impressive top-end power. Then, along came the better-flowing 4.0L with a bore and stroke of 3.88x3.41 inches. The 4.0L made good top-end power, but didn’t offer the extreme low-end grunt of the 4.2L 258 engine. So, by taking the 4.2L crank and rods of the 4.2L and sticking ’em in the 4.0L, you get a 4.6L or 4.7L stroker (depending on overbore) with the torque of the 4.2L, as well as the top-end jab of the 4.0L.

But what does that really equate to in terms of price, power, and hassle? Both Hazel and Trasborg have installed stroker engines. In both cases, the strokers required larger 23-24lb/hr injectors to run properly, so add a couple hundred bucks into the mix. A newly remanufactured 4.0L long block will set you back roughly $1,800. A new stroker long-block will cost about $3,800. So, how much more does that $2,000 get you?

For Hazel’s ’99 XJ Cherokee running the factory AW4 auto, NP231 T-case, 4.88 gears, and 33-inch tires, the factory 4.0L made 133hp/176 lb-ft stock at the tires. After adding a header, after-cat exhaust, cold air intake, the 4.0L made 152hp/200 lb-ft. Replacing the 4.0L with a 4.6L stroker and 24 lb/hr injectors resulted in 172hp/224 lb-ft. Finally, a very expensive dyno-tune session with a custom Unichip programmer got the power level up to 184hp/235 lb-ft.

For Trasborg’s ’91 MJ Comanche running an AX15 manual, NP231, 4.56 gears, and 33-inch tires, and a cold-air intake on the factory 4.0L made 138hp/177 lb-ft. Replacing the 4.0L with a 4.7L stroker, header, and larger injectors resulted in 161hp/230 lb-ft.

In Hazel’s case, the stroker was worth an additional 20hp/24 lb-ft initially and 32hp/35 lb-ft after roughly $1,000 in dyno testing and Unichip product. In Trasborg’s case, the stroker was worth roughly 23hp/53 lb-ft, although Trasborg isn’t done testing yet. Trasborg’s more drastic torque increase is most likely because of the automatic tranny in Hazel’s.

So again, is the stroker worth it? If your 4.0L is completely blown and you need a full long-block replacement, we’d say maybe. Especially if you can do a lot of the rebuild work yourself to keep costs down. What the peak numbers used above don’t tell is the increase in torque down low, which really helps overall drivability. However, when you consider the $2,000 difference in price between the remanufactured 4.0L and the stroker long-block, you could buy all the bolt-on knick-knacks for your 4.0L and still have enough money left over to regear your axles, which probably help drivability more than just the stroker. It’s food for thought.

JK Boom
Q My JK has no power. Should I do a supercharger on my 3.8L or swap engines?

A We’ve been told first-hand by the engineers who designed the 3.8L that it is nowhere near as durable as the 4.0L it replaced. Adding levels of boost above 4-5 psi puts the piston ring lands, rod bearings, or rods in jeopardy of catastrophic failure. For those reasons alone, we’d personally shy away from spending any real money on supercharger or turbocharger kits for the 3.8L.

As for the engine swap, many JK guys tend to gravitate towards the 5.7L Hemi engine and 545RFE five-speed auto from the Ram pickup and SUV platforms. They’re a better fit than the Dodge/Chrysler car engines. However, it’s not an inexpensive undertaking, with some turn-key conversions topping out near the $30,000 mark. More and more companies are coming on line offering GM Gen III and Gen IV swap options for the JK like MoTech (, which offers full turn-key conversion or builder parts for the do-it-yourselfer allowing full integration of the new GM engine with the JK’s can bus system.

Power Up
Q What’s the best bolt-on mods for my 4.0L or 2.5L?

A We’ll start with the 4.0L first. It’s an engine that readily responds to increasing its ability to breathe. In this order and as funds allow, we’d first install a good cold-air intake setup, an after-cat exhaust, header, 62mm throttle body, and finally a low-resistance set of plug wires. These mods will get you about 20hp at the rear tires.

For the 2.5L MPI engine, we’d again start with the cold air intake, but would leave the factory muffler in place unless it’s cracked or damaged. We’ve found that low-restriction, after-cat systems decrease the exhaust gas velocity and hamper low-speed cylinder scavenging. Next, we’d replace the exhaust manifold with a header only if the stock manifold is cracked. Finally, we’d install a 60mm throttle body from a 4.0L engine and then an electric fan in place of the factory engine-driven fan. These mods will get you about 11hp at the rear tires.

Q My 4.0L/3.8L/2.5L exhaust manifold is cracked. What should I replace it with? Why do they all crack?

A One of these days you’ll fire up your Jeep and will be greeted by a nauseatingly loud tick, tick, tick from a cracked exhaust manifold. Even if you can’t hear it, it’s still probably cracked. It’s most common on the thin, tubular factory manifold on the 4.0L and now the cast iron manifolds of the 3.8L V-6. The 2.5L is more durable, but not immune.

Why? Most Jeep engines are calibrated on the lean side to help the boxy, unaerodynamic vehicles meet federally imposed mileage requirements. By injecting less fuel into the engine at light- and medium-load conditions, less fuel is used (duh). Unfortunately, with leaner mixtures comes higher exhaust gas temperatures. The exhaust manifolds are subjected to extremely high heat, which weakens and ultimately cracks the manifold material.

Welding isn’t an option because in almost all cases the crack will just reappear up or downstream of the weld repair. And replacing with a new or good, used factory part just buys you time until it happens again. In just about all cases, the real solution is to go with a quality aftermarket tubular header built of thicker material that can withstand the high exhaust gas temperatures.

Q What’s the best programmer for my JK?

A The cop-out answer is the programmer that offers you all the features you want at the price you can afford. Sorry, but it’s true. Nowadays electronic programmers (or tuners as they’re more commonly known) come in all levels of price, performance, and options. You can turn on or off factory gizmos like daytime running lights, tire pressure sensors, calibrate throttle bodies, increase performance, disable sway bars, enable lockers, and so much more.

When selecting your programmer, focus your attention more on getting one that offers as many of these kind of features you’re looking for rather than the manufacturer’s power increase claims. In reality, they all offer fairly similar power increases because there’s only so much ignition timing and fuel map manipulation you can add.

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