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Answers to all your Jeep questions

Posted in How To: Tech Qa on January 23, 2018
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Photographers: Jp ArchivesCourtesy of the manufactures

JK Ratio Right
I have a ’11 Wrangler JK Unlimited with the 3.8L V-6 and an automatic transmission. What axle gear ratio would be best with 35-inch tires?
Karl Anderson
Via facebook.com/JohnCappa4x4

The 3.8L V-6 and automatic transmission found in the ’07-’11 Jeep Wrangler JK generally need all the help they can get when backed up with larger-than-stock tires. The ’12-’18 Wrangler 3.6L and automatic transmission is a much more venerable powertrain combination. The smaller 3.6L makes 85 more horsepower than the 3.8L, making axle gear selection on the early-model JK even more important. The axle gear ratio you choose for your Jeep will depend on other factors beyond tire diameter. Driving habits should be considered too. If you do a lot of high-speed highway runs you generally will not want to over-gear your Jeep. It will result in increased engine rpm, unnecessary engine wear, reduced fuel economy, and a slower top speed. In most applications, with normal driving habits, you’ll usually want to back up the 35-inch tires with 4.88 gears. However, if you live in the mountains, frequent very hilly areas, or rarely run at top speed on the highway, you might be better off with 5.13:1 or even 5.38:1 ratio axle gears. The lower gears will make your Jeep feel sportier with a snappier throttle response. Don’t forget to correct the speedometer. There are several handheld controllers available that plug into the OBD II port of your Jeep that will give you the ability to let the computer know that the tire dimeter and axle gear ratio have been altered. A corrected speedometer will not only give you an accurate speed reading, the powertrain computer will be better able to manage the engine tune and transmission shift points as well. In extreme cases, an uncorrected speedometer could lead to the transmission overheating and ultimately failing. It’s a cheap and easy electronic upgrade you can do at home in less than 20 minutes. Companies such as AEV (aev-conversions.com) offer a controller to correct the speedometer on the JK Wrangler.

JK XJ Swap
What do you think about swapping JK Dana 44 axles under an XJ Cherokee? I can get a straight factory housing for $100. I have a used JK Dana 44 with everything sitting in the bed of my truck that I picked up for $100. I can get a Dana 44 crate axle with 5.13:1 ratio gears and an Eaton ELocker for $2,300. I'm just wondering which housing is better.
Mark Fosbinder
Via facebook.com/JohnCappa4x4

Swapping the JK Dana 44 axles into the XJ Cherokee is totally doable. In some cases, many of the factory JK axle suspension brackets can be retained. The factory Jeep JK Dana 44 front axle housings have been known to bend when backed with tires that are 35 inches in diameter or bigger, or in applications where the vehicle is driven aggressively. However, a built JK is usually heavier than most built-up XJs. The factory JK axlehousing may be fine. Of course, it will depend on tire size and driving habits. As you have found, there are alternatives to the bend-prone factory JK Dana 44 front axlehousing. The Dana (spicerparts.com) Ultimate Dana 44 front axle features nickel chromoly steel axleshafts, heavy-duty 5/16-inch-thick axletubes, and 1/4-inch-thick suspension brackets. This axle is said to be good for up to 37-inch tires. The other option is to take the JK Dana 44 guts that you already have and put them into a heavy-duty Dynatrac (dynatrac.com) ProRock 44 housing. The Dynatrac housing features much more heavy-duty, larger diameter axletubes, a more robust reinforced cast centersection with increased ground clearance, and heavy-duty end forgings, among other things. In the end, the Dana Ultimate Dana 44 crate axle is better than stock, but not as strong as the Dynatrac ProRock 44 axlehousing. Which housing you choose will depend on how you plan to use the XJ and how heavy you think it will be.

Radius Revolution
How long are the radius arms that you put on the Garage Project GPW? I'm building a 2x4 steel tube frame Willys right now and considering all of the different suspension setups.
@j900rr
Via Instagram @cappaworks

The radius arms I used are the front arms from a ’99-’04 Land Rover Discovery II. The rear radius arms on this Land Rover model are a little different than the fronts and don’t offer the ground clearance I wanted; that’s why I used the fronts at all four corners. Plus, now I only need to keep one spare around, although the arms are forged and incredibly stout with very large bushings that don’t seem to wear easily. Land Rover used radius arms on other models and years as well, the ’99-’04 simply suited my application best.

The farthest two bolt holes on the ’99-’04 Land Rover Discovery II radius arms are 40 inches apart. The effective length (measured from the pivot end to the axle centerline) is around 36-37 inches. I retained the factory wheelbase on my GPW, and the front and rear arms nearly meet in the middle of the frame. A big advantage of this design is that the suspension pivot points are now moved to the thickest and strongest part of a flatfender frame. The tapered ends of the flatfender frames have been known to crack when used hard off-road for many years, especially around aftermarket Saginaw steering box mounts, the leaf spring pivots, and shackle mounts.

The disadvantage of using radius arms like these is that they do not provide massive amounts of suspension articulation. I’m only using 10-inch-travel coilover shocks. The shock mounting I used allows for around 11-12 inches of total vertical travel per corner, which can be tough to manage on a short-wheelbase Jeep like a flatfender. The driveshafts are short and could easily bind with any more wheel travel than that. If you plan on extending the wheelbase and are shooting for more articulation, you might be better off with three- or four-link suspensions front and rear. Although, it’s hard to beat the radius arms for their overall simplicity, low cost, durability, and ease of setup.

Rust Ready
How much rust is too much rust? My dad has what is left of his ’78 CJ-7. It’s been sitting in pieces and full of pine shadows for close to 30 years outside. He said it was rusty back in 1987. My dad said the body mounts were shot on it so he bought a fiberglass tub. I want to attempt to throw my money at it and restore it since it was his first car and it’s a Renegade Levi Edition.
@joyboy13257
Via Instagram @cappaworks

Nearly anything can be restored. It’s all a matter of time and money. It’s hard to say if your dad’s Jeep tub is worth rebuilding without seeing it in person, and even then the value of such a body tub will depend on who you talk to. Having grown up a West Coast guy, I don’t have much tolerance for rust. I’ve chopped up and recycled body tubs that East Coasters would kill for. So it really depends on your perspective, how much bodywork you are willing to do, what parts you have access to, and of course sentimental value. Fortunately, companies like Omix-Ada (omix-ada.com) offer replacement body parts and repair panels for all of the popular Jeep models. If you decide that your body tub is too far gone, Omix-Ada offers complete body tubs too.

Leaky Spicer 18
I have a ’69 CJ-5 that I just finished a frame-off restoration on. I have an oil leak at the rear output shaft on the transfer case. I have read that I need to block a small hole in the face of the transfer case with a special style gasket so that the oil from my transmission won’t spill over into the transfer case. Have you heard of this? The Jeep is all original and stock. It didn’t leak before I tore it apart to rebuild everything. It has a Buick V-6, T-14 transmission, and a Spicer 18 transfer case.
@djharris85
Via Instagram @cappaworks

There are many jokes that could be referenced about old Jeeps leaking oil of some sort. The Spicer 18 is a notorious leaker, and the design provides many places where the fluid can escape. Some older transmission and transfer case assemblies allow oil to flow from one to the other, but this shouldn’t be the reason the rear output on your Spicer 18 is leaking. There are three possible causes for your leak. You should start by wiping the area clean with some brake cleaner and a rag to find out exactly where the oil is coming from.

If oil is leaking from the rear output yoke seal surface, check the rear output seal condition as well as the seal surface on the rear yoke. When installing a new seal, sometimes the spring wrapped around the inside of the seal can get knocked off. If this happens, the seal surface may leak. Also, older yokes, especially those that spend a lot of time off-road and caked in dirt, can have a damaged seal surface. The dirt and grime built up on the seal can eventually wear a groove in the yoke seal surface, allowing oil to escape. If the groove is deep enough, you may need to replace the yoke. Companies such as Omix-Ada (omix-ada.com) and Tom Wood’s Custom Drive Shafts (4xshaft.com) have replacement Spicer 18 yokes.

If oil appears to be coming from the yoke nut in the center, the oil is passing the yoke splines. You will need to remove the yoke and make sure it’s still a good, tight fit. If it’s loose on the splines, it should be replaced. Clean the yoke splines and output shaft splines thoroughly with brake cleaner and smear a little bit of silicone on them prior to reinstalling the yoke and torqueing the nut.

You may find that the leak is not coming from the rear output at all. It’s not unusual for the Spicer 18 to leak past the shim stack on the rear output or from one of the rear output retaining bolts. To fix this leak you’ll need to remove the rear output and shims and clean each shim mating surface carefully. Clean the bolts and bolt holes as best you can. Spray each shim with spray gasket and let them tack up before restacking them. Spray gasket is available from companies like Permatex (permatex.com). Use thread locking compound on the output bolt threads or smear silicone on the threads prior to reassembly. Not all of the bolts are wet bolts, but it won’t hurt to hit them all. These bolts have been known to loosen up and leak oil.

Sometimes the Spicer 18 can trick you into thinking the leak is from the rear output. The wind from driving down the road can cause an oil leak from further up to splash rearward. If you are unsure about exactly where the leak is coming from, it might be a good idea to wipe down the whole transfer case, transmission, and engine. I’ve even seen a leaky front pinion seal fling oil up and make it appear as though the transfer case was leaking, so check everywhere. Good luck with your leak search and destroy.

Mileage Master
I recently saw a sudden drop in in fuel economy on my CJ-8. It has a swapped-in ’00 4.0L and an AW4 four-speed automatic. It was hitting as high as 17 mpg on the freeway, but now it gets around 12 mpg. It does have a shake at cruising speed, but I’m not sure if it’s related. I have been running 4.56 gears and 35-inch tires for a long time.
Robert Riegelsberger
Via facebook.com/JohnCappa4x4

Most Jeeps running the 4.0L inline-six and AW4 four-speed automatic transmission will get a combined (highway/city) fuel economy of around 17 mpg with stock-sized tires. With 35-inch tires, I would expect a combined fuel economy of around 15 mpg or so. The drop to 12 from 15-ish is easier to understand. However, there are many things that can alter the fuel economy of your Jeep, including a small change in your driving habits and improper tire air pressure. If the check engine light is not on and there are no codes to read, it’s always best to start with the easy and cheap stuff. A dirty air filter could cause a significant drop in fuel economy. Even one dusty trail outing could influence mpg. The engine has to work harder to draw air in through a dirty filter. Other things under the hood to consider are the spark plug and plug wire assembly condition. Are the spark plugs worn and in need of replacement? Are any of the contacts loose or corroded? Are the plug boots in good shape?

You could also have a clogged injector or an oxygen sensor going bad. You might want to pull the spark plugs and check them. An over-fueled rich condition will be indicated by a wet or black spark plug. They should be chocolate brown, although most 4.0L engines run a little lean, so there could be some white coating on them.

It’s also possible that you have a catalytic converter going bad. If the catalyst rattles loose inside and turns sideways, blocking the exhaust flow, you’ll see a drop in power and fuel economy.

Adding weight to your Jeep will surely affect fuel economy. Changing to a different brand of 35-inch tire could cause a drop in fuel economy. Some 35-inch tires are heavier than others. The rule of thumb is that adding 10 pounds of wheel and tire weight is the equivalent to adding 100 pounds of cargo weight when it comes to acceleration, fuel economy, and braking. The weight of different brands of 35-inch tires can vary as much as 20 pounds per tire! That would be the same as adding as much as 800 pounds of cargo or four large people to your Jeep.

Keep in mind that the addition of lift kits, heavy-duty aftermarket bumpers, body armor, roof racks, and other wing-dings will punish fuel economy in the form of added weight and wind resistance.

The shake at cruising speed could be a cause for concern. Is the transmission shifting properly? Is it shifting into top gear when it should, or is something simply worn-out and not working as efficiently as it could be? You have a bit of searching to do.

Budget Diesel Swap Bubble Burst
Would you ever swap a GM 6.2L diesel into a Jeep? I could see it as an inexpensive alternative to the 2.8L Cummins crate engine.
William Peavy
Via facebook.com/JohnCappa4x4

I can’t imagine a scenario where a 6.2L GM diesel swap would make sense. So no, I would never make that engine swap in a Jeep. I’m not trying to be mean or anything, it’s just not a cost-effective engine swap that would have any advantages at all. First and foremost, almost no diesel engine swap will ever pay for itself unless you have access to free or a very cheap engine and labor. In most cases, a diesel engine swap will take around 10 years to pay for itself via the increased fuel economy, and that’s only if you average 12,000 miles a year. This of course does not take into consideration the additional costs associated with a diesel, such as more expensive oil changes.

The GM 6.2L diesel came in a few different variations. The least desirable would be the early 130hp model that produced 240 lb-ft of torque. This engine makes less power and weighs more than most modern Jeep engines. The best of the Jeep 4.0L inline-six gas engines were made from ’01-’06. They put out 190 hp and 235 lb-ft of torque. Even glancing at these numbers makes it pretty clear that the Jeep 4.0L would be a better swap candidate, not to mention that you could simply buy many Jeeps that already have the 4.0L installed under the hood from the factory.

There is also a 160hp version of the 6.2L that spins 285 lb-ft of torque and a 185hp 6.2L that punched out 330 lb-ft of torque. Used versions of these engines can be found relatively inexpensively, but they are still hardly worth swapping into a Jeep. Let me explain. If you are going through all the work to put a GM-based engine in your Jeep, you likely want to make the conversion for more power. If you want to make more power than the engine you are replacing and want to do it cheaply, it’s really hard to beat a Chevy 350 with a TBI on it. All the swap parts are readily available and there are not a lot of unknowns when swapping a Chevy V-8 into a Jeep. Now, if you simply want something that’s unusual and requires much more work to swap in, regardless of the fact that it makes less power, then the 6.2L GM diesel is a great swap. Also, you can’t really make up for the lack of power by throwing aftermarket parts at the 6.2L diesel because you could throw less money at the Chevy 350 and make more power. Sorry to burst the 6.2L diesel bubble.

Rubicon Envy
How do I convince my wife to let me sell our car and buy a Wrangler Rubicon Unlimited? I have a YJ and she says I already have a Jeep.
Nolan Crow
Via facebook.com/JohnCappa4x4

You have a couple of options if you want to get your backside into a newer Jeep with the consent of your significant other. Some methods are more devious and illegal than others. One thing to remember that most men forget is that women often worry about our safety, and rightfully so. Let’s face it, we’re pretty stupid and we do stupid things all the time to impress or entertain ourselves and our friends. With that in mind, you could let the little lady know that you are genuinely worried about the reliability and safety of your old Jeep. It doesn’t have airbags or the same crash rating as a modern Wrangler Rubicon Unlimited. How could she possibly feel good about sending you down the road in that YJ death trap?

If you’re a horrible liar and don’t have a convincing bone in your body or your wife responded by letting you know she just decided to up your life insurance policy, you might have to consider a questionably legal route of getting into a new JK. Of course, stealing a new JK will be a short-term solution as you will eventually get caught driving the Jeep down road, and we all know how those car chases on TV end up. You’ll have to be smarter about it, although the end result could still be that you end up in jail. What if you were to upgrade the insurance policy on your Jeep? It could be increased to say maybe the same price as a new Rubicon Unlimited? Of course, you’ll likely have to provide photo proof to the insurance company of just how awesome your imaginary YJ is and defend your need for additional insurance. You could simply print out any number of images found online. Once the YJ is insured to the moon, it’s time to crack a fuel line, throw a road flare under the hood, and go wheeling! With your YJ totaled and burned to the ground, you can now collect your insurance, buy the new Jeep, and hopefully stay out of jail long enough to enjoy it for at least a little while.

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