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April 2008 4x4 Tech Questions - Techline

Posted in How To: Tech Qa on April 1, 2008
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Address your correspondence to:
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.fourwheeler. com. Due to the volume of mail, electronic and otherwise, we cannot respond to every reader, but we do read everything.

Question: I need some help with a discbrake conversion. I purchased a '71 Bronco, and I'm trying to turn it into a functional trail vehicle. One of the things I want to do is convert the brakes from drums to discs. It has a Ford 9-inch in the rear and a Dana 44 in the front.

Everyone and their mother wants to sell me a kit to do this for several hundred dollars, which is more than I want to spend. Do you know how I can do this on the cheap? Which over-the-counter rotors and parts could I get and make work with the appropriate brackets or with a little fab work? I know I can not be alone in this, as the Dana 44 and Ford 9-inch are way popular.
Brian Wensel
Fort Mohave, AZ

Answer: I will have to agree that those early Bronco brakes leave a lot to be desired. A disc-brake conversion is not cheap, no matter how good of a scrounger you are. Brakes are a pretty important item, especially when your life depends on them. However, with a bit of forethought and maybe some luck in finding the parts, you can do the conversion without too big of a dent in your wallet.

The easiest way would be to obtain the complete front end and/or brake system from a '76-'77 Bronco. The chances of finding such are slim to none, and if you do get lucky, it's going to be pricey. So let's settle for second best.

There are several ways you can do the front conversion, but this seems to be one of the better ways. Starting out, you can't use the original master cylinder, so you will have to obtain one from a '76-'77 Bronco that was originally equipped with disc brakes, along with hubs and rotors. Then you're going to need a bunch of parts from a '74-'75 1/2-ton Chevy pickup or Blazer. Yes,said Chevy-sorry about that, Ford purists. This will include the spindles, calipers, backing plates, and a bunch of small parts. Take a look at node/73 and it will outline just what is necessary to make this all come together.

For the rear, things are also pretty easy. Rock Equipment (916/434-7887, sells some brackets you can use, and then you come up with your own parts, or you can buy the parts and pieces directly from them. Having an emergency brake is not only a necessity but the law, so keep this in mind when doing the rear conversion.

Keep in mind before you start on this kind of a project it is going to set you back a considerable amount of money to do it right, but there is only one way to do brakes, and that is the right way.

Question: I just recently bought a '99 Jeep Wrangler Sport with the threespeed auto tranny. It has 31x10.50 BFGoodrich A/T tires on it. It's not a daily driver, but when I do drive it to and from work, it chugs the gas. The last time I filled it up, I got 12 mpg. I looked at the original window sticker and it said it should get 15-19 mpg.

I plan to put the K&N filter on it, but I really want to get the revs down at highway speeds to help reduce the wear and tear on the motor. It only has 48,000 miles on it. The traf-fic flows between 75 and 80 mph to and from work. Is there a bolt-on overdrive that I could put on it? If so, about how much do they cost, and what are the pros and cons?
Brandon Spell
Silsbee, TX

Answer: Yep, your Jeep probably should be getting a lot better fuel mileage than 12, but not at 80 mph. To start off with, just because others are driving at 80 mph doesn't mean you have to. Have you ever thought about leaving for work, say, 10 to 20 minutes earlier and driving at a steady 60 to 65 mph? My guess is that your fuel mileage would then be about 18 mpg.

Oh, and something to keep in mind is that you can't figure fuel mileage off of just one tank fill-up and be accurate. Different nozzles shut off at different percentages of tank fullness. Even the air temperature can affect when the nozzle shuts off. Just a gallon more, or less, than the last fill-up can make a big difference when figuring fuel mileage.

An overdrive would be a great improvement, but unfortunately there is not a bolt-on unit for your Jeep's three-speed automatic or behind the transfer case. Gear Vendors (, 800/999-9555) lists one for the Dodge 203 transfer case (similar if not the same as the one in your Jeep), so you might want to contact them to see if your application would fit, which I am sure it would. The problem is that the overdrive unit is quite long, which would make for a very, very short and impractical-length driveshaft. Even so, you would have to drive a heck of a lot of miles to get any payback, as the price installed would most likely be in the $3,000 to $4,000 range.

I think that the best thing to do would be to swap in an AW-4 four-speed overdrive automatic from a Jeep Cherokee. This is a very doable swap, but how much it would cost depends on just how good of a deal you get on the AW-4 and how much of the work you plan to do yourself. My guess is when it's all said and done, if you do the work it would be under $1,000. Under Google, I typed in "TJ transmission swap" and found several Web sites that could lead you through the process.

Question: I've got a question about headers for an '06 Dodge Ram 1500 4x4. I am thinking about replacing the stock exhaust manifolds on my Ram with headers. The only thing slowing me down is my lack of knowledge of the difference between shorty, mid-tube, and long-tube headers. What would be the best for a truck that is daily-driven?

The Ram already features an AEM intake and a Flowmaster Super 40 exhaust. In my mind the long-tube headers sound like they will hang too low, and the shorty headers might need some extra add-on pipe to get to the existing Y-tube. Is the mid-tube the answer for a direct replacement? What are the advantages of each type?
Nate Richmond
Huber Heights, OH

Answer: As a general rule for street and off-pavement performance, you want to go with small-diameter tubing, and the tubes should be as long as possible without interfering with any of the driveline components, as well as going into a long collector. The small diameter of the tubes keep the flow speed up, and the long tubes prevent the gases from a reverse flow under negative pressure waves. My opinion is that there is not a lot to be gained with short-tube headers. On a previous Dodge project vehicle, we put some very nice, and expensive, short-tube headers on the 360ci motor and in reality I felt that it was a waste of time, effort, and money for the little we gained in performance.

Naturally, long-tube headers will cost more because of the fact that there is more material, and a lot more time in the design. Long-tube headers sometimes can be a real pain to install, and in some instances it is even necessary to take off a motor mount and slightly lift the engine in order to gain installation clearance. The shorter the overall length of the header, the easier it is to install.

The Flowmaster 40-series muffl ers are an excellent choice. They will give some great sound and are great for a truck that sees off-pavement use as they are quite solidly built.

Question: I currently own a '97 Chevy Z71 and I have a set of older Rally rims off of an '86 fullsize Blazer. I was wondering if I will need a lift to clear a set of 32-inch tires.

I was hoping to go no higher than maybe a 3-inch body lift, if any at all, because this truck gets used a lot hauling trailers and also a slide-in camper.
Craig McKenzie
Carthage, NY

Answer: I know that the Z71 package carried a lot of options that were grouped together, and one was a higher ride height of about 2 inches. This should allow plenty of room for the 32-inch tires, and in fact most likely the tires on the truck in a metric size are pretty close to 32-inchers.

The wheels off the Blazer have a backspacing that was designed for a solid front axle. The IFS wheels have a lot more backspacing. In other words, the Blazer wheels will stick out past the fender opening and put more load on the suspension and steering components. There also may be a clearance issue around the front brake calipers, but perhaps not because of the backspacing. I asked Dennis Franklin of Franklin Tire and Suspension in Yuma, Arizona, for his opinion on such a wheel swap, and this is what he had to say:

"The old-style Rally has 4 inches of backspacing, and the 16-inch Z71 has almost 6 inches of backspacing. One must also keep in mind that the Z71 wheel is 7 inches wide and the 15-inch Rally wheel is 8 inches wide. Combine these, and it means that the center of the tire will stick out 21/2 inches beyond what the factory intended. To make matters worse, the scrub angle goes to pot, causing the tires to slide around a turn. Not good for long or smooth tire wear.

"The factory tire was a 32x10.50R16. You can put on a 32x11.50R15; just make sure that you trim the fenders both front and rear because the tire will now swing in an arc, taking up more room in the fenderwell.

"Oh yes, and your friendly frontend man will love you too. Whenever you tweak up the torsion bars a little, and add high-offset wheels and tires, this then causes the idler arms and pitman arms to go south before winter, and the upper ball joints and control-arm bushing will also be very unhappy. Not a very good idea to swap wheels, in my opinion."

If you should decide that you want more tire clearance, I wouldn't recommend a body lift if you plan to use a slide-in camper. Using body spacers under the bed would perhaps put more of a leverage load on the mounts than they were designed for.

Question: We have an '07 Wrangler Rubicon Unlimited with 35s and several hundred pounds of racks, winch, and gear. We tow a 3,500-pound camping trailer, but even with 5.13:1 gears, there just isn't enough power-really not even enough for daily driving without the trailer. I don't need to race anyone, but I do want to make it up hills. I need torque. Is there a turbodiesel swap that wouldn't require me to rob Fort Knox? Or another suggestion- maybe a blower?
Brian Dunning
Laguna Niguel, CA

Answer: Yep, you're right, that is the biggest complaint with the new JKs. The V-6 just doesn't make enough power. There are some headers available and an air filter change, but together, these really aren't gong to make the power you're looking for. I am sure in time that the aftermarket will be supplying a blower for the V-6. I understand that Adventure Innovations (805/322-7001, is in the process of developing a supercharger kit for the JK and may have it available by the time you read this.

The problem is that most of the diesels you could swap will not make the power you're looking for, or would not meet emissions standards. Burnsville Off Road ( has made some conversions using the '07 3.0L Mercedes engine. A really nice engine, but my guess is it's also really expensive.

You also might consider putting your Jeep on a "diet" if possible. You are towing the Unlimited's absolute maximum rated load (3,500 pounds) and with bigger tires, "several hundred pounds" of bolt-ons, a full tank of fuel, and a couple of full-grown adults and their gear riding inside, you may well be exceeding the vehicle's gross combined weight rating, which really hurts both power and fuel mileage.

Question: Regarding "Lower Gears for Durango Axles" (Techline, Jan. '08):

The front axle of the '05 Dodge Durango in question is the Corporate Chrysler 8.0 (205 mm), not a Dana 30. They have been using this axle beginning with the '00 model year in the first-generation Durangos, and it has continued in the second generation as well. The earliest Durangos ('97-'99) used a Dana 35. I've seen up to 4.56:1 gearing available for the Corporate 8.0 with no change to the carrier required. I've heard this is the same front axle that is used in late-model Ram 1500s. I don't have any input on the strength of this axle.

The 8.25 is used in the rear, which I find interesting, being that the first-generation models (which didn't offer Hemi power) were available with the larger 9.25 axles.

By the way, what is meant by a "floating" axle? I tested my 9.25 and it sunk.
Joel Smith

Answer: Yep, I blew it there with my answer. You're completely right. My only excuse is that I had some brain fade when I was in the process of answering three different letters on Chrysler axles and must have gotten my fingers on the wrong line of my gear chart.

Yes, there are some aftermarket 4.56:1 gears available from places like Randy's Ring & Pinion. The lowest factory gear is 3.92:1, and yes, the lower gears will bolt right up to the present carrier. And yes again, the Chrysler 8-inch is also used in the front of IFS Dodge 1500-series pickups starting in 2002.

As to the rear end, it could be either an 8.25 or the much stronger 9.25-inch with 31-spline C-clipstyle axles. Thanks for keeping me straight.

As to your question: A "full-floating axle" is one where the wheel is mounted to a hub with bearings on the inner and outer portions, which in turn rides on a hollow spindle that is either an integrated part of the axlehousing or bolted on. The spindle/hub carries all the weight, not the axleshaft. The axle is slid through the spindle and can be removed without taking the wheel off. In other words, the axle "floats" and carries no weight and just acts as a driver. This is common on 3/4- to 1-ton pickups.

On a "semi-floating" axle, the wheel is bolted directly to the axleshaft. The weight of the vehicle is carried on one bearing on the outer end of the shaft and by the differential assembly on the splined end of the axleshaft.

Question: I've been a loyal reader of your magazine since I was 14 years old when I became bitten with the 'wheeling bug. Probably the part of your magazine I have enjoyed the most over the years is "Techline." I have always found the advice given in your column to be quite informative.

In the April '06 issue someone with a Suzuki/Ford 302 had a question as to which transmission/transfer case combination would suit him best. I'm sorry to say that your response had a few errors in it. First, the low range of the NP207 transfer case is not 2.72:1, it is only 2.61:1. The 2.72:1 ratio was used in the NP231 and 241 transfer cases. Second, you stated that you would not use the C4 transmission but rather swap in an AOD because it offered a lower First gear and an overdrive. While the AOD does offer an overdrive, the First gear ratio is actu-ally slightly higher than a C4. The AOD uses a 2.40:1 first and a 1.47:1 second while the C4 uses a 2.46:1 first and 1.46:1 second gear. The only Ford automatic that uses substantially lower gearing than this was the 4R70W (for all purposes, an electronically controlled AOD that utilized a wide-ratio gearset), which used a 2.84:1 first and 1.55:1 second. The 4R70W's overdrive isn't nearly as steep either at 0.70:1 compared to the AOD's 0.67:1.

In my opinion, he should use the C4.While only being a three-speed auto, it is very light and saps very little torque from the engine. In fact, it is in the same class as the Powerglide in the amount of power it uses to operate. Durability shouldn't be a serious issue either, because the C4 can be seriously beefed up with better turbine (input) shafts, larger servo piston(s), and replacement steel six-pinion input planetaries to replace the failure-prone stock aluminum three-pinion planetary. The C4 doesn't require a computer to operate it, either (neither does an AOD, I guess).

Even if the AOD was geared lower, I wouldn't use it due to the power flow in Third and Fourth gears, non-selectable lockup feature, and the fact that its shift pattern uses a crappy three-quadrant setup which only offers Overdrive, Drive, and First, with no selection available for Second. While you can get a Second gear by manually shifting from First to Drive and then back into First before the transmission can make the shift into Third, this is not a good idea. It will quickly fry the OD band and direct clutch, as well as eliminate engine braking in second.

You also can't get away from the lockup feature due to its entirely mechanical nature. Plus the 60/40 (60 percent mechanical, 40 percent hydraulic) torque flow in Third gear isn't the best either, especially in high-load, low-speed situations when a vehicle would need all of the torque multiplication of the torque converter in these situations (or at least more multiplication than this setup will offer). There is an aftermarket turbine (input) shaft offered that will entirely eliminate the OD lockup feature and split torque flow in Third, but this can add a lot of heat to the transmission, especially during extended cruises in OD. All of these problems are addressed by certain aftermarket companies, but the cost of all of these modifications usually raises the cost of a rebuilt AOD to anywhere from $1,200 to $2,000. Ouch! You could use a later-model version of an AOD (an AODE is better, but the 4R70W is best), but it would necessitate the use of an aftermarket stand-alone computer or swapping in a new engine/transmission combo from a donor vehicle.

I think he should stick with the C4. It's lighter, just as strong, sucks less power, is simpler in design, doesn't need a computer, and costs much less to rebuild/modify. And if you want a lockup torque converter, get a C5. The C5 is nothing more then a C4 with a lockup torque converter.
S. Krein

Answer: Thanks for catching me on this. You seem to be very knowledgeable about Ford automatics. You're right, I did make two mistakes, though I should have gone into more detail in my answer. I say most AODs because there were actually some AODs that had the 2.84:1 ratio right from the factory. Even if they are hard to locate, the parts are not. I don't have a current SVO Ford Racing Catalog, but my old one lists an AOD wide-ratio upgrade kit that basically uses the 4R70W transmission gearset. Art Carr has a similar kit available.

Yes, you did point out some problems with the AOD transmission and how expensive it would be to rebuild to solve these problems, but you also made note of the modifications needed to beef up the C4. I don't think that $1,200 to $2,000 is out of the ballpark when it comes to a performance automatic transmission. The performance transmission guys tell me that the AOD can be made plenty stout and handle any amount of power that the 302 could put out.

Oh, I will agree with you as to the C4 being the better transmission to use for his conversion.

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