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June 2009 4x4 Truck Repair & Tech Questions - Techline

Posted in How To: Tech Qa on June 1, 2009
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Address your correspondence to:
Techline Four Wheeler
6420 Wilshire Blvd.
Los Angeles, CA 90048.

All letters become the property of Four Wheeler, and we reserve the right to edit them for length, accuracy, and clarity. The editorial department also can be reached through the Web site at www.four Due to the volume of mail, electronic and otherwise, we cannot respond to every reader, but we do read everything.

Wants 20 Inches And Rockwells For Bronco
Question: I have an '87 Ford Bronco (the big one). There's only a 6-inch lift on it now, but sooner rather than later I'm gonna fab up a custom 20-inch lift (or so) and have 46-inch-or-larger tires. I want to go big and bad on some new axles and I need a little input. I hear all the time about guys installing the Rockwell axles on the 4x4s, but I never get enough information on the subject. Here's what I came up with: I want front and rear 2 -ton Rockwells with four-wheel steer (hydraulic assist, I guess). Does this sound anyway possible or sane?
Jon Henning
Salisbury, NC

Answer: While I was not able to come up with a Rockwell/Ford conversion the first place you should look is our own website ( Run a search of our archives, and you'll find some good Rockwell tech data, as Ken Brubaker offers a lot of straightforward information on these axles. Same goes for our sister publication Jp ( Just keep in mind that your project will be expensive, take a lot of time and lots of custom fabrication.

How To Turn A 4-Inch Lift Into Six
Question: I've been studying and reading up on suspension systems and lift kits for a long time, but I can't figure this out, so I figured I'd ask someone who would know. I have a '99 TJ and have already installed a Skyjacker 2-inch coil spacer lift. When I install my 4-inch suspension lift, will it be possible to put the coil spacers on top of the new springs and make my 4-inch lift a 6-inch one?
Will Reaves
New Edinbrug, AR

Answer: Yes, you can include the 2-inch spacers with the 4-inch kit for a total of 6 inches of lift. However, it may not be without problems. You definitely will need to go with a slip-yoke eliminator kit, and you most likely will need longer shocks and/or shock brackets, longer sway bar links, longer bump stops, a different track bar or mounting bracket,a different pitman arm, rear shock relocation brackets, and perhaps a few more things.

I took a look at Skyjacker's website, and while they listed part numbers for the components in one of the 6-inch lift kits, they didn't list them for the 4-inch kits, so I was not able to compare component parts. It would be a good idea for you to give the tech department at Skyjacker a call (318/388-0816) before you install the 2-inch spacers.

Keep in mind that Skyjacker's 6-inch kit uses heavier control arms and relocates them from the original position. Otherwise, the angle that they would operate at would be quite steep and result in increased load to the mounting points, as well as what I would describe as "really bad ride quality" due to the fact that the front axle would have to move forward before it starts any upward movement. (If you have noticed, the Jeep engineers placed the control arms almost parallel to the ground.) Any suspension lift will cause a downward angle of the control arms, and the greater the lift, the greater the angle, and hence poorer ride quality.

WJ Grand Cherokee Engine Fire Concerns
Question: I have a '99 Jeep Grand Cherokee. A friend said that he read an article in a four-year-old Consumer Reports magazine about Jeep Grand Cherokees catching fire under the hood. Is this something that I should be worried about?
Joe Reardon
Los Angeles, CA

Answer: Only if your Grand Cherokee has the 4.0L six-cylinder and not the V8. Yes, there was a recallas covered in Safety Recall # B06. It seems that a bunch of Jeeps that used the 4.0L motor escaped from the factory without a special debris shield in place. This affectedsome--but not all--1999-to-2002 WJ Grand Cherokees, 2000-01 XJ Cherokees, and 2000-02 Wranglers.

If your vehicle has the letter "S" in the 8th position of the VIN, then you should take your Cherokee to a Jeep dealer and have him check to see if the shield is in place. If not, have him order and install the Debris Shield Package number 6BVCB060.

TH400 Swap For Cracked 700R4?
Question: I have an '85 Chevy -ton 4x4 with the 700R4 automatic in it, and the tranny case is cracked. I'm just wondering if a Turbo 350 or 400 will fit in the same place as the 700R4, mount-wise and lengthwise, to mate with the transfer case and driveshafts?
Richard Petersen

Answer: That is an easy one to answer in just one word: No.All three transmissions are different lengths; the TH 350 is 21.5 inches, the 400 is 24.25 inches, and the 700R4 is 23.376 inches long. They have different mounting locations and take a different adapter to your NP 208 transfer case. The 400 has a different output-spline count at 32, versus the 700R4's 27-spline count. They also have two different output shaft lengths. While I believe the output splines on the 350 are the same as the 700R4, there are some length problems. Advance Adapters sells a special kit (p/n 50-7100) that includes a new adapter, output shaft, kickdown cable, and special dipstick tube. This will allow you to use the same driveshafts.

However, I think that you would be better off finding a new case for your 700R4 and having it rebuilt. This would be my choice of transmission for your truck because it features not only a lower First gear but an Overdrive to improve fuel mileage on the highway. The early ones got a bad rap, which seems to still stick with them, but with the latest pieces and parts, it can withstand any punishment you can put to it.

Now about the case breaking--this usually happens when someone has been "jumping the truck." There are braces that extend from the motor to the lower part of the cast-aluminum dust cover on the front of the transmission. It's pretty common for these to be missing, especially if the motor has been replaced. It's important that these braces be in place to prevent the case from breaking as yours has.

Proper TJ Towing Techniques
Question: What is the proper method to tow my four-cylinder, standard-transmission Jeep TJ? I believe it has a 231 transfer case.
Steve Schardt

Answer: The rear driveline turns the internal pump in the transfer case and lubricates the sprockets and gears. Leaving the transmission in gear helps protect it by not letting the gears rotate. If they rotated, they would tend to seize the gears to the shaft due to lack of lubrication. I know you're going to say, "But the gears turn when the vehicle is being driven." Yes, that is right, but when it is being driven, all the gears are turning. When being towed, only a few gears are turning, and these don't provide enough movement of the gear lube to all the gears for full lubrication.

Wondering About "Questionable" Jeep V-6
Question: I was reading Willie's Workbench in the January issue ("Jeep Engines De-Mystified") and it seemed like a nice solid article about the engines until it got towards the end. I don't understand how an engine can be questionably 210 horsepower? Is it advertised as more powerful than it is? Less powerful? Isn't it against the law to falsely advertise something like that? I just didn't like how it was considered questionable without posting any facts or anything. (It was even called questionable twice in the article.) I would love to know more as I am on my third Jeep now, an '07 JK with this "questionable" engine in it. Thanks in advance.

Answer: Perhaps questionable was not the proper word to use. Most people, especially those with automatic transmissions, feel that the motor lacks the power of the 4.0-liter, which was rated at 190 horsepower. Yes, vehicle manufacturers have to adhere to certain guidelines when posting horsepower and torque figures, but I suppose likeeverything in the real world, there are some "fudge factors" involved. (Go check with your local tire dealer and ask him how many tires advertised as 35x12.50-15s actually measure a true 35 inches tall.)

Perhaps it's the higher weight of the JK versus the TJ, or the fact that the V-6 makes its horsepower and torque at a much higher rpm--the vehicle just seems to lack the power that it should have. There wasnothing derogatory being applied to the motor. The last "questionable" was because the motor has not proven itself to be as reliable as the 4.0L as of yet.

Just as a side note, I have driven and/or owned vehicles with every one of these engines that I listed over the years, so I have a pretty good handle on how they feel "rated," horsepower-wise, as well as their dependability.

Transfer Case for GM 5.3L Wrangler?
Question: I have a question about which transfer case I should use. I have an '88 Jeep Wrangler with a 6-inch lift and 35-inch tires. I bought a wrecked '07 Tahoe 4x4 with a 5.3 and auto trans. I'm going to put the 5.3 and auto trans in my Jeep, but am not sure which transfer case to use. The Tahoe transfer case also has the on-dash switch which I was thinking would be cool to have--a Jeep with no shifters in the floor at all. My stock transfer case is a NP231 with a 2.72 ratio. The Tahoe has a NP246 with a 2.72 ratio.

What are my options or what should I do? Do I get an adapter and use my NP231? Does the NP231 need to be "beefed" up? Is the NP246 stronger and ready to go? Do I need to get a second job and save for an Atlas II?
Aaron Miller
Marshall, TX

Answer: At first thought it just might be cool to have an electric-shifted 246 transfer case in your Jeep. This large heavy-duty transfer case was used by GM since about 1998 and is found in everything from Tahoes to Escalades. However, I could give you a million reasons why you don't want to use it in your Jeep. I don't have anywhere near that much time or space so I will just pass on some highlights.

To start out with, it uses an electric speedometer drive, while your Jeep uses a mechanical speedo. It's an active transfer case, which means that it has the ability to alter the amount of torque sent to the front axle when the computer senses wheel slippage. To do this, it has an internal clutch pack that relies on speed sensors that monitor the speed of each axle as well as that of the driveshaft, which feeds this information to a computer. This in turn locks up the clutch packs to provide the needed amount of power to the proper axle. The computer also tells the front axle when to engage the front axle shift motor to lock the axleshafts together. One of the big problems with this system is that all the tires must be the exact same height or it will trigger a trouble code. To say the least, it is a very complex operating system that requires a special scan tool to troubleshoot and quite a bit of experience using it. Sure it could be done, but the wiring would be truly a nightmare.

By all means stay with the 231 transfer case. It's simple, and surprisingly quite strong. If you're worried a bit about its overall strength, there are several modifications that can be made, such as replacing the planetary gears with the strong six-pinion system and wider chain from the 241 case, and using an aftermarket 32-spline output shaft. Rockland Standard Gear (877/774-4327, has some already built up that way or you can order the parts and do it yourself.

Now with that said, you still may have a problem with the automatic transmission control module trying to send some strange signals to the trans because the 246 transfer case is not wired into the system. You may have to end up using a 2WD ATC for things to function properly. Bet Mike Weinberg at Rockland could give you the proper information to make it all work together.

As to the engine swap, well that is pretty straight forward and there are several kits on the market to make the installation quite easy.

Letter Of The Month
"Low" vs. "High" Gear Ratios
Question: Here is a question that has always bugged me. When I read about changing ring and pinion ratios in a differential, I understand how you divide the number of teeth on the ring gear by the pinion gear to get the gear ratio. What I don't understand is why a lower gear ratio is not as strong as a higher gear ratio. Oh, and why is a 5:1 ratio considered a "lower" gear ratio while 3:1 is considered a "high" gear ratio?
Mark Casey
Belgrade, MT

Answer: The first question is pretty easy to answer. The ring gear is a given size in diameter. For instance, a Ford 9-inch rearend actually refers to the ring gear being nine inches in diameter, regardless of gear ratio. With the 3:1 ratio, for every three turns of the driveshaft (as it's connected directly to the pinion gear) the ring gear will turn one complete revolution. In this example, the ring gear will have 39 teeth and the pinion gear will have 13. Let's go to the extreme just to make it more dramatic, and pick a 6.50:1 gear ratio. The ring gear would still have 39 teeth on it, but the pinion gear will have less than half that many with only 6 teeth. What this also means is that to get a proper mesh of the gear teeth, the pinion has to be considerably smaller, which also means that there are not only fewer teeth but also a lot less contact area on the ring gear teeth, which also relates to less strength.

As to the second part of your question. When the driving gear has fewer teeth than the driven gear, then the driven gear will turn at a lower speed than the driving gear. So a 6.50:1 gear ratio turns at a lower speed than a 3:1 gear ratio, hence the term "lower" gear ratio. Think of a cement mixer. The electric motor has a very small pulley on it, while the pulley that turns the drum is quite large. The drum turns at a much lower speed than the electric motor does. Hopefully that clears it up for you.

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