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Answers to all your Jeep questions

Posted in How To: Tech Qa on February 3, 2017
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Straight Swap

So I have a question, and I think the answer is "no problem!" In fact, I'm sure it is. Still, can you confirm that my 3.21:1 geared Dana 30 front axle from my ’12 two-door Jeep Wrangler Sport will work in a ’13 four-door Jeep Wrangler Unlimited Sahara that also has 3.21:1 geared axles? Should be plug-and-play, am I right?

Dan
Via email

There is often a lot of confusion about the differences between the Jeep JK Wrangler and JK Wrangler Unlimited. The Unlimited model is simply a derivative of the standard two-door Wrangler. This means that they share a lot of parts, including the engine and other drivetrain components, suspension, and chassis bits. However, you may see slightly different spring rates and shock valving between the two- and four-door models. The parts are still interchangeable, and only an expert would likely be able to tell the difference if you were to swap the two-door parts onto the four-door.

As for the complete front axle housings, they are identical between the ’12 and ’13 models. It will be a direct bolt-in swap. Just make sure that the Jeep receiving the swap truly does have matching 3.21 axle gears. You can check the small steel tag attached to the differential cover, but the best method is to remove the cover and check the gears themselves. Somewhere around the circumference of the ring gear you will find several different numbers. For 3.21:1 ratio gears you should see a 45/14 stamped into the gear. This identifies the number of ring gear teeth (45) and the number of pinion gear teeth (14). If you divide the ring gear tooth count by the pinion gear tooth count, you will get the actual gear ratio, which in this case is 3.2142857. This is rounded to 3.21. If the ring gear does not have any numbers stamped into it, you can always just count the teeth on both the ring gear and pinion gear.

It’s important to be aware of what you are purchasing when it comes to axles, especially Jeep JK front housings. It’s not uncommon to find used stock JK front axles that have been abused with 37-inch tires or bigger. Many of these housings are bent. Check the housing for straightness. Other notoriously worn components include the ball joints and unit bearings. Also, inspect the control arm and track bar mounting brackets for cracks, shoddy repairs, and wallowed out boltholes. Anything that looks abused, probably has been. Ideally, you should look for a front axle that still has the factory paint on it, including on the underside where it gets worn away quickly off-road.

JK Transmission Temping

I have a ’10 JK Unlimited with some modifications, but everything is street legal, even though my big girl does very well on the trail. At the risk of making this too long, I need to give you some history and set the stage. Some time ago, I installed a gauge pod so I can see some instrument readings which the folks at Chrysler didn’t feel were necessary. One was the engine oil pressure and the other is the transmission oil temperature. For the engine oil, I installed a sandwich adapter, and I am pulling pressure on the output side of the filter. Much to my surprise, the pressure at idle drops as low as 20 psi but quickly ramps up with any throttle activity. With 68,000 miles and some minor engine performance mods, I have no engine issues at all, but I have always run AmsOil oil.

I installed the transmission oil temperature sensor on the return line coming out of the transmission cooler, right next to the oil pan. This temperature will rise to as high as 220 or more during hot days. I know the transmission cooler fins are in good shape and are also clean. My winch is in front of everything, but it is not blocking very much air movement. The fan is functioning normally and has no issues.

Normally, the temperature only rises high while driving on the street. On the trail, I typically do not see high temps. This high temp issue bugs the hell out of me. After working with two transmission shops, both say the oil and flow is good. There is still a temp issue after a purge and refill too. The transmission shop also suggested adding another cooler in the circuit to get the temp down. I am not sure why everyone wants me to install a second cooler to assist in what the first cooler should have been designed to do on its own. I have written some specialty shops in search of a cooler that will perform better to replace the current one I have, yet I have had no response to it actually performing any better. A Chrysler service tech near me states the service temp under 260 is considered acceptable.

I would certainly prefer to replace the transmission cooler with one that is actually designed to work, but that seems to elude me. I have drawn up a circuit and found the correct components to install a switch and relays, which in one position will force the fan on 100 percent, a second position will prevent the fan from running in deep water, and a third will put the fan in normal operating mode. I am hopeful that running the fan at 100 percent on hot days will get the temperature down, but not certain on the impact of the engine coolant. My goal is to get the temperature down to a consistent running temp of 180-ish and not to exceed 200. Have you heard of this type of problem before on the JKs? Can you offer any words of wisdom or expertise? After reading the November ’16 issue, I thought I would drop you a note specifically on my problem. I love Jp, and I look forward to reading the articles. The 75 Years of Jeep series was great!

Scott B
Louisville, OH

It would have been much more helpful if I knew the exact modifications you have made to your Jeep to help you diagnose the hot automatic transmission problem. I’m not sure of the street legal laws in Ohio, so as far as I know you could be running 40-inch tires with 3.73:1 ratio axle gears and have your Jeep loaded down with 1,500 pounds of body armor and camp gear, which would certainly pose more than one problem.

Typically you want the transmission temperature sensor mounted in the oil pan. This will provide the most accurate reading of the fluid that is being sucked up by the transmission oil pump and distributed throughout the transmission. Having the temperature gauge sensor in the fluid return line will likely read a little higher than in the pan, although I can’t tell you by how much.

Ideal automatic transmission temperature is less than 185 degrees. Maintaining this temperature will ensure that your transmission lives a long and happy life. Increased overall vehicle weight, larger than stock tires, aggressive driving, long steep grades, lugging the engine, and loose terrain such as sand and mud can cause automatic transmission temperatures to increase.

The first place to start is gearing. If you’ve added a lift and larger tires without regearing the axles and correcting the speedometer, this could be your culprit. Two things are happening here if so. First, the larger diameter tires alter the final drive ratio, causing the engine and transmission to work harder, which in turn creates more heat. Second, not correcting the speedometer confuses the powertrain computer. It’s programed to perform certain functions such as shifts at a specific rpm and vehicle speed. The larger tires will fowl that up if the speedometer is not corrected.

If you are running 35-inch tires, you should consider 4.56 or 4.88 axle gears. Upgrading to 37-inch and larger tires will require 5.13 or 5.38 gears. The deeper gears will give the engine and transmission more leverage to deal with the larger diameter tires. They will also help correct the speedometer. However, regardless of what gearing you decide to go with, you’ll need to correct the speedometer anytime you alter tire diameter or axle ratio gearing. Companies such as AEV (aev-conversions.com), Hypertech (hypertech.com), and Pro Comp (procompusa.com) all offer programmers for the Jeep Wrangler JK and other models. The programmers electronically correct for different tire diameters as well as axle gear ratio changes.

Now, if you have the right gears matched up to the right tire size and you still have a transmission temperature problem, you’ll want to install an additional transmission oil cooler in conjunction with the factory transmission oil cooler. Ultimately, you need more surface area to help dissipate the heat. You have many different options. Lots of aftermarket transmission oil coolers are available, some even have their own fans so they can be mounted almost anywhere on or under the Jeep. Flex-a-lite (flex-a-lite.com) offers a Translife transmission oil cooler kit for the ’07-’14 Jeep Wrangler JK, which includes the oil cooler and mounting brackets for a bolt-on installation. The cooler kit is available with either 3/8-inch push-on barb hose fittings or -6 AN fittings.

LED Headlight Swap

Lead me out of the darkness. Can I retrofit the optional ’17 Wrangler LED headlights to my ’07 Wrangler?

Bob Rief
Cardiff, CA

Only some ’17 Jeep Wrangler and Wrangler Unlimited models will receive the new LED headlights and fog lamps. They will be a Mopar option on the Sport and Sport S and standard on Sahara and Rubicon models. I have not seen the ’17 wiring in person yet. However, I suspect it will be a plug-and-play upgrade for older JKs. If it’s not, I’m sure an aftermarket pigtail harness will certainly be made available quickly. The Mopar LED headlights are $595. No word on if the current Mopar LED headlights will be replaced with the factory ’17 Wrangler LED headlights. At this time, they are not the same part. Right now, it’s unknown what the price for the factory Jeep LED headlights will be. However, it’s very likely that they will far outprice many of the different bolt-on aftermarket LED headlight kits already available for the ’07-’16 Wrangler today. So if you really want the LED headlights, you’ll likely be better off going with aftermarket LED headlights from companies like J.W. Speaker (jwspeaker.com), Max-Bilt (maxbilt.com), Mopar (mopar.com), Putco (putco.com), Rigid Industries (rigidindustries.com), Vision X (visionxusa.com), and several others. All of these companies offer LED headlight kits that have been designed specifically to bolt into the JK Wrangler without any guesswork.

Rubicon Ready

I recently signed up for the Jeepers Jamboree. I own a ’14 Jeep Rubicon X Unlimited. I emailed the Jeepers Jamboree staff and they say that my Jeep is capable of handling the trail. They even added that they have seen the same exact Jeep model go through without any problems. Furthermore, I've read online about how capable the Rubicon X is fully able to do the trail since it is, after all, named after it.

However, after reading Nena Knows Jeeps (Apr. ’16), the confidence in my Rubicon X has lowered a whole lot. Not because it was a horrible article but because of the reality of it. How you said that the terrain changes all the time, and all the upgrades you mentioned was an awakening. My upgrades are limited to the Rancho Rock Gear control arm protection and differential skids. My Rubicon already came with rock sliders, but are they good enough? Also, my tow hooks are factory. I figured they are more capable than other Wrangler models.

Since you're an independent party, and not a part of Jeepers Jamboree, could I get your expert advice whether my Rubicon X needs all the upgrades you mentioned in the article or will I be comfortable enough (with less stress) with it as-is?

Ron Sioson
Via email

The Rubicon Trail is extremely unpredictable and the trail conditions change dramatically depending on the season. Fortunately, Jeepers Jamboree (jeepersjamboree.com) runs the trail in the summer when the weather and trail conditions are more predictable and less extreme. However, keep in mind that the historical Donner Pass is only about 50 miles from the Rubicon Trail. Bad weather can come in quickly and unexpectedly nearly any time of the year. We’ve been on the Rubicon in the middle of September where it was 80 degrees on the first trail day, and snowing on the last.

Anyway, the Jeepers Jamboree crew does a really good job prepping the trail and helping first timers like you get through. Your Rubicon X should have no trouble getting through. Of course you’ll get a few dings and scrapes on the underside of your Jeep, but that’s to be expected.

The factory rock sliders on your Jeep are attached to the body. They can withstand a few unexpected bumps and dings, but I would not recommend using them as real rock sliders. The mounting brackets can bend and tear out of the body if you beat on them too heavily. Personally, I would recommend some heavy-duty aftermarket rocker guards. You don’t necessarily need them for the Rubicon trail, but they will certainly make the trip more stress free for you. Well-built rocker guards are usually the first modification I recommend for anyone planning to take their Jeep off-road.

Your factory tow points are more than adequate for the Rubicon trail. Ultimately, you want to make sure that you have at least one tow point on the front and rear of the Jeep. Although, two tow points per end can be ideal when trying to pull and maneuver a Jeep through a difficult section.

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