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Answers To All Your Jeep Questions

Posted in How To: Tech Qa on September 1, 2016
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Weak Link or Not
First of all, I love the magazine. However, I do have a beef to pick with you. In "Ratio Right" (Oct. ’15), Ali Mansour states that "shifting the weak link to the 1310 CV as opposed to the ring and pinion was a safer option overall." In the same issue, in the Your Jeep section, John Cappa tells Curt McKay, who says he wants to make the U-joint the weak link, that "engineering a weak link into anything is a foolish move in most, but not all, cases," mainly citing collateral damage. The Jeeps are similar with 37-inch tires and 5.13 gears, but his is a lighter two door. Shouldn't you guys be roughly on the same sheet of music when writing about the same thing? So which one is the real deal, weak link or not?

Axel Virzi
Roanoke, TX

Jeep building opinions and experiences vary dramatically. Ali Mansour provided his opinion based on his experiences, I simply provided mine. In reality, even though you engineer what you might think is the weak link there is no guarantee that is where the failure will occur. Metal components like axleshafts, locking hubs, gears, yokes, driveshafts, and U-joints can have unknown imperfections and can fatigue at different rates over time. Even if everything is new, installing a 1310 U-jointed driveshaft instead of a 1350 ’shaft is no surefire way to pinpoint the weak link. If the driveshaft binds at full droop, it will likely be the failing point regardless of what other weak link you install.

Now, when a driveshaft U-joint does fail, it’s rarely a simple easy fix that only requires the replacement of a U-joint. In my experience, nine times out of 10, there is other collateral damage caused by a driveshaft failure. There is usually a lot of torque and/or rpm involved in driveshaft failure. Once a U-joint breaks, the driveshaft is likely to fling around wildly under your 4x4. It can hit and damage the engine oil pan, transmission oil pan, wiring, fuel lines, exhaust, and so on. It can also smash itself against a rock or other obstacle on the trail. Flinging driveshafts regularly get dents in the tubing, making them unusable, even if you have a spare U-joint. I’ve also seen busted driveshafts come back around and smash into the transfer case, or bind up and cause the transmission and transfer case to scatter. Replacing the ring-and-pinion would be a lot cheaper than a repair bill for a transfer case or transmission. In almost every driveshaft failure I have seen, one of the yokes on the axle or transfer case becomes damaged, requiring replacement. The U-joint retaining hardware will also need to be replaced. The broken U-joint shown (see image) looks like it would be easy to replace, but this low-speed, low-rpm failure resulted in a bent unusable driveshaft. It had only hit the vehicle frame fairly lightly.

If you insist on attempting to make the driveshafts the weak link, I would recommend adding some sort of driveshaft hoop to keep it in check when it does bust free. You’ll likely want to carry a spare driveshaft, as well as replacement yokes and U-joint retaining hardware.

Ultimately, I simply think it’s a smarter and safer long-term decision to install quality driveshafts with the proper-sized yokes and U-joints. This will ensure that you don’t end up stranded on the road or trail. Having said that, I’d still recommend that you carry spare U-joints and driveshaft hardware just in case.


37s versus 35s
I’ve been considering replacing the 35-inch tires on my Jeep JK Rubicon with 37s, and I was wondering if you could help me out. I’m honestly not sure if it’s worth it? I know you wheel yours (as do I), but it’s a big change for what I’ve read only really amounts to an extra inch of clearance. I want the same tires you have (they’re one of the few out there that makes a good mud tire that will fit my 20-inch wheel). The Jeep has an automatic transmission and 4.88 axle gears. I recently added an EVO Manufacturing bolt-on coilover suspension. I’ve done my drivelines and just about every other upgrade you can think of at this point. I plan to do axleshafts and add high-clearance fenders (I’m leaning toward XRC full armor or MetalCloak fenders). Any info you could give me that would help me decide would be great!

Chris Scott
Via email

In my opinion, you’ll be better off with sticking with the 35s, unless you eventually plan to upgrade the complete axle assemblies. The JK Wrangler Dana 44 axles are about at their serviceable tire size limit with 35-inch tires. The 37s will eventually cause several different axle components to fail. The first to go will likely be the ball joints and wheel bearings, then the axleshafts, and then the ring-and-pinion and Rubicon locker. The factory housings also bend, even with 35-inch tires. All of these factory axle components are designed to work together, so strengthening only one area doesn’t help the whole assembly.

If you do decide to go with the 37s, you’ll likely find that the axle gears need to be deeper than 4.88. You’ll generally want 5.13 or 5.38 gears on a Jeep JK with 37-inch tires. For true off-road performance, I think the 20-inch wheels are holding you back. Your Jeep will ride smoother and the aired-down 35-inch tires will be able to envelop obstacles much better with 17-inch wheels. That extra bit of sidewall makes a big difference in ride and traction. However, if street canyon-carving performance is more important to you, stick with the 20-inch wheels. The lower-profile sidewall is less likely to roll and squirm when cornering hard on the street.


Oil Temp Query
I was drooling over, er, browsing the AutoMeter gauge selections the other day, trying to decide what I want to get for my next project. In addition to the standard half-dozen gauges (tach, speedo/odometer, fuel level, coolant temp, volts, and oil pressure), I’m planning to have an engine-hour meter (which will be more consistent for maintenance intervals than mileage) and an air-pressure gauge for my onboard air system. I found a series of oil temperature gauges specifically for Jeeps (at least, they have the Jeep logo on them), which included engine, transmission, transfer case, front axle, and rear axle. What purpose do they serve? I know that automatic transmissions shouldn’t be overheated because the ATF breaks down. I assume the same goes for transfer cases that use ATF or an equivalent. Under what circumstances would it be necessary to monitor axle lube temperatures or engine oil temp? My Jeep has a GM 350 V-8 (stock with about 200 hp), NV4500 manual transmission, Spicer 18 transfer case with a 4.86:1 low range, and Ford 9-inch axles front and rear with 4.57:1 ratio gears. None of these components use ATF to my knowledge. They all use gear oil of one kind or another, except, of course, for the engine, where I usually run 20W-50 for the Arizona desert. Would I gain anything by monitoring the temperatures of these units? If so, what would normal temperatures be and how far above normal could I get before I’d have to worry about damage? How different would engine-oil temperatures be from coolant temperatures?

Dave Peterson
Via email

You’re right! AutoMeter (autometer.com) offers a gauge for just about every application you can imagine in many different designs. What you may not know is that the AutoMeter Custom Shop (ampcustomshop.com) can assemble custom gauges. This is a great option if you have specific colors or artwork that you want to implement on your gauges.

Anyway, the number one killer of automatic transmissions is heat. So as you mentioned, a gauge for an auto transmission makes perfect sense. For maximum transmission life, the ATF fluid should not exceed 175 degrees, measured at the transmission oil pan. To maintain this temperature you may need to add a larger transmission cooler, increase airflow by relocating the cooler or adding an electric fan, or install a finned aluminum deep-sump transmission oil pan. High-horsepower vehicles and vehicles that haul heavy loads are more susceptible to hotter transmission fluid temperatures, but off-roading in deep mud, sand, rocks, and even snow can cause an automatic transmission to overheat. When the ATF fluid heats up beyond 220 degrees, varnishes form, seals harden, and other transmission damage begins to occur, significantly shortening transmission life.

In most cases, manual transmissions (like yours), transfer cases (gear-driven and chain-driven), and axles do not overheat. However, if you haul heavy loads at high speeds for long periods of time in high ambient temperatures, these components could potentially overheat. A temperature gauge for a manual transmission, transfer case, or axle is probably a bit of overkill on a Jeep, though. The only time I could see these components getting hot is if something is worn or broken inside, improperly set up, or if the oil level is low. Gear oil-filled components should not be allowed to operate at consistent temperatures above 250 degrees. Most components in good working order will run at around 150-160 degrees. The use of synthetic oils can drop gear oil temperatures by 10-20 degrees and finned aluminum differential covers can also help dissipate heat more quickly than smooth steel covers.

Older engines like your GM 350 V-8 run best with coolant temperatures at 180-200 degrees. Newer engines run slightly warmer to help decrease exhaust emissions and increase fuel efficiency. Ideal engine oil temperatures are typically between 230 and 260 degrees. Monitoring engine oil temperature can simply help you spot an internal problem more quickly than relying on the oil pressure and water temperature gauges. Engine oil temp gauges are usually reserved for high-dollar or high-horsepower engines that require expensive replacement parts. Catching a failure quickly and shutting down early can mean the difference between replacing bearings and tossing the whole rotating engine assembly in the garbage.


JK Wrangler Gauges
To start, thank you very much for a wonderful magazine and source of information on all our Jeeps.

I have a ’12 Wrangler and have come across a problem that many people may be having. I drove fire engines for about 30 years before retiring and was constantly watching my gauges for problems. The new Jeeps don't have gauges, and it makes me nervous. A while ago I purchased an A-pillar gauge pod and added a voltmeter and an oil pressure gauge. The ’12 Wrangler was the first year of the Pentastar V-6. I have taken it to several places and can’t find anyplace that will connect the oil pressure gauge without charging me hundreds of dollars to remove and reinstall lots of engine components just to get to the oil sensor. Even then, they say it's a real difficult fit. I have heard somewhere that some people are drilling and tapping the oil filter cover and connecting the sensor there, but it's plastic and doesn't sound like a safe thing to do. Can you offer any suggestions for a simple place to connect?

Gary Schultzman
Yucaipa, CA

It’s unfortunate that the ’07-’13 Jeep JK Wrangler and Wrangler Unlimited don’t have gauges that display actual number values for drivers that wish to know. The ’14-current Wranglers with the Electronic Vehicle Information Center (EVIC) are able to provide this information. You simply use the buttons on the steering wheel to toggle through actual coolant temperature, oil pressure, transmission temperature (automatic only), and oil life remaining. Obviously, this doesn’t help you or other ’13 and older Wrangler owners. But don’t fret; you can still get accurate oil pressure reading on your Jeep.

The ’07-’11 3.8L Wrangler can use a traditional oil pressure gauge. To connect it, you can use a Glowshift (glowshiftdirect.com) oil filter sandwich adapter for 3/4-16 oil filter threads (PN GS-AF2). This aluminum Glowshift adapter fits between the engine block and the factory oil filter. It features three 1/8 NPT ports that can be used for oil pressure or oil temperature sensors. Two NPT plugs are included to fill the ports you don’t use. It’s a simple bolt-on procedure. If you can change your oil, you can install the Glowshift sandwich adapter.

The Pentastar V-6 in the ’12-current Wrangler doesn’t use a traditional block-mounted oil filter. It is a canister-style filter and connecting an aftermarket oil pressure gauge is a little more involved. We have seen people drill, tap, and add a fitting to the oil filter canister cap, but it’s made of plastic and not an ideal install. It seems that someone could easily manufacturer and sell anodized billet aluminum Pentastar oil canister caps, especially if the caps had NPT ports for easier oil pressure and temperature gauge installation. Unfortunately, we don’t know anyone making them, yet. However, you can use a Bluetooth performance interface module such as the DashBoss (dashboss.com) to read actual engine oil pressure and many other parameters on your iPhone, iPod Touch, or iPad. The DashBoss will work on all ’07-current Jeep Wranglers, as well as many other Jeep vehicles.


YJ Wiring
I've been reading Jp now for about 10 years. I started my ’95 YJ project about two years ago. I don't remember seeing anyone discussing the lack of an aftermarket chassis wiring harness for the end of production YJs. The original harness is shot, and I'm upgrading to a TPI small-block Chevy engine with its own engine harness. Since the YJ uses a Chevy-style column, can I adapt a Chevy 4x4 truck harness to this project? I'm also reconfiguring the entire dash with AutoMeter gauges, but the heater/wipers/signals/lights would still be factory. If the Chevy harness won't work, any other suggestions would be greatly appreciated!

Robert Alford
Barboursville, WV

The wiring harness on an older Jeep is often the first component to deteriorate. It’s also not uncommon for the wiring harness to have been chopped up and molested by previous owners. You have a couple of options. You aren’t retaining most of the factory circuits, so you can pare down whatever harness you choose. While it may be possible to modify the Chevy harness, it may be easier to simply find a stock replacement chassis harness. You could try contacting Collins Bros. Jeep (collinsbrosjeep.com) for a used wiring harness in good condition. The company specializes in new and used Jeep parts as well as complete used and restored Jeeps. You can also commonly find used harnesses on eBay (ebay.com). Option three is to go with a universal or ’87-’91 YJ harness from Painless Performance (painlessperformance.com). Again, you’ll have to cut out or tie up the circuits you don’t need.


Trail Finder
I live in western Arizona where there is an abundance of trails to drive. So many cross each other that at times it is difficult to decide which fork in the track to take to get where you intend. I’ve tried to use Google Earth and online topo maps to help eliminate the confusion, but both have limitations and drawbacks. For example, the topo maps don’t seem up to date as there are lots of new trails that they don’t show. Google Earth is up-to-date, but you can’t get it when you’re off the grid. Pulling Lat-Lon coordinates from either and putting them in my GPS is cumbersome and often leaves me confused.

Is there a means of getting a finite chunk of Google Earth downloaded to an iPad or laptop that can be interfaced with GPS that I can take with me on the trail (off the grid)? I could then locate my actual position, zoom in and out when desired, and make good course decisions. Someone must have this figured out, and I’d sure appreciate knowing how.

Jim Snow
Via email

Finding and staying on the correct trail can be tough in some open areas like Arizona with lots of tracks. You might consider trying a guidebook from FunTreks (funtreks.com). The company drives many trails in a particular area and then selects only the best. The books include images of the scenery you can expect as well as trouble spots. Each trail has a custom-designed map and precise turn-by-turn directions with GPS waypoints. In addition, the company offers data cards for your GPS with tracks and waypoints that match what you see in the books.

If you really like topographical maps, you might consider a Lowrance (lowrance.com) navigation system. The newer and more complex Lowrance units can be loaded with satellite topo images that allow you to track, mark, and plan your route. You can also zoom in and out to find the best path.

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