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June 2010 Techline

Posted in How To: Tech Qa on June 1, 2010
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Where To Write
Address all correspondence to: Techline Four Wheeler, 831 S. Douglas St., El Segundo, CA 90245. You can also reach us by e-mail at; be sure to type the words "Tech Line" in the subject line. All submissions 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 Due to the volume of mail, electronic and otherwise, we cannot respond to every reader, but we do read everything.

Unequal Gears in Fullsize Bronco
Q. I have a 1988 fullsize Bronco. I was mudding and broke the spider gears in the rearend, so I went to the junkyard and pulled a new one. Come to find out the rearend ratios do not match. I was thinking, "Well, what's going to happen next time I lock it in? Wouldn't it either push or pull the front end because they are not the same? Could it break the transfer case because of too much stress, or maybe the universal joints?" The old rearend was a 3.54:1 and the new one is a 3.55:1. Not much difference, but the new one is way heavier, and the gears look much bigger. To make things worse, it is sitting on 39.5 Super Swampers. It has a five-speed manual transmission. I am trying to see what I am up against with possible problems and/or solutions. I need it to be cheap because I am still in school. Would it be ok if it was only locked in on dirt or sand considering that the tires are always slipping and sliding anyways?
Tyler Zaneski

A. First, that little difference in gear ratio, front to back, will not make a bit of difference. Most likely, differences in tire diameter will make more of a difference in overall gearing than what you have in the difference in gears. Yes, having a different gear ratio, front to rear, is pretty common, especially when the front is a different manufacturer, model, or size. It just has to do with the number of teeth on the ring and pinion gear versus the overall diameter. If the gear ratio is radically different, like 3.54:1 and 3.73:1, then you have a problem with one axle trying to turn faster than the other. Then some thing has to give, be it tire slippage or breakage in the driveline.

Now, as to the gears in the new rearend being larger: your truck came from the factory with what Ford refers to as an 8.8-inch axle. The numbers stand for the diameter of the ring gear, 8.8 inches. My guess is that you put in a rearend out of something other than an '81-97 Ford F-150 or Bronco. If the rearend came from another Ford truck of a different year, then it just might be the more desirable Ford 9-inch. The 8.8 has a removable rear cover while the 9-inch has a complete differential that comes out the front of the housing. Some of the early Ford heavy-duty 1/2-tons also used a Dana 60 rearend, which also had a rear cover plate. If so, someplace on the housing casting you should see an embossed number "60."

Dana 60 Shoppers' Tips
Q. I am looking to build a beefier axle for my 2000 Dodge Ram 1/2-ton with the 9.25-inch rearend. I am looking for a Dana 60 rear. I'm on a budget, so I'm primarily looking for the housing first, and then I can get aftermarket parts after that. What vehicles has the Dana 60 rear been in?
Ben Bishop
Oak Grove, KY

A. The Dana 60 has been in a lot of vehicles and available with several different bolt patterns, as well as different widths and spring mounting locations. The number of applications is way too large to list here.

Probably the best thing for you to do is measure from the wheel mounting surface of one side to the wheel mounting surface of the other. Then, with this information, start your search in wrecking yards, keeping in mind the difference in the wheel bolt pattern you may find. The more common bolt pattern you're going to find is a standard 8-bolt pattern on a full-floating rearend. Any of the five-bolt pattern axles (5-on-51/2) will come from the '70s Fords, IHs, and some Dodges that had the 440ci engine package. Don't forget that you will also have to match the front and rear gear ratios.

Ford Tailpipe Louver Mysteries
Q. I just bought a used F-250 with the 6.4L Powerstroke diesel. I am really happy with the truck, but one thing really bugs me. The tailpipe tip has some funny louvers punched into it that extend into the tip. Just what are these for? No one at the dealership can tell me anything.
John Boyd
Santa Barbara, CA

A. They do look strange, don't they? But they do have a purpose, strange as it seems. Your truck has a particulate filter on it to catch what some people call diesel soot. Every once in a while, the computer says it's time to clean out the filter, so an extra amount of fuel is dumped into the filter and actually burns out the soot that it has caught. This causes the tailpipes to get extremely hot, and the louvers in the tip are designed to draw outside air into the tailpipe to cool off the exhaust and to prevent damaging the paint or anything that comes close to the exhaust. Unfortunately, this system also plays havoc with fuel mileage. (Just another measure that the EPA required truck manufacturers to add.) And to your next question, no, it cannot be removed.

Revisiting GM's Beloved Insta-Trac
Q. I bought a '90 Chevy 1/2-ton pickup from my uncle. Believe it or not, it has been stored in a barn for the last 10 years or so, and only has 56,000 miles on it. He got mad at it one day because he got stuck in a snowbank, and when he tried to put it in four-wheel drive, the front axle would not engage even though the transfer case was shifted. So he parked it. I've got it running and have replaced the tires and changed all the fluids, but I am finding that some days it will go into four-wheel drive, and some days it will not. I have been stuck enough times to the point where I'm about ready to again park it in the barn for another 10 years. I did notice that there appears to be some kind of a device on the axlehousing with some wires going to it. I did some asking around, and a mechanic told me the truck had a two-piece front axle on this side, and that this "motor" (that's what he called it) with wires coming out of it locks the two axle shafts together. Okay, but if this is the case, then why doesn't the other tire have traction? Can you help me out? I really like this truck but without four-wheel traction here in upper Michigan, the truck is worthless.
Josh Randal
Paradise, MI

A. It has been along time since I have received a question about the '88-'97 trucks not going into four-wheel drive. The first vacuum-shift four-wheel drive system that Chevy used was not the brightest idea, especially for a manufacturer building trucks in Michigan.

They use what they called a Thermal Linear Actuator. That "motor" is nothing more than a cylinder holding some special gas, a piston, and a heating element. When you shift into four-wheel drive, an electrical switch closes, allowing current to flow to this actuator. The current goes to a heating element that heats the gas, which then expands and pushes the piston down the cylinder. The piston is connected to linkage that engages a coupler that in turn connects the axle shafts together. In very cold weather, or when packed with snow, the thermal actuator does not get warm enough to heat the gas sufficiently to cause the piston to move.

The aftermarket, including companies like Warn, tried to solve the problem early on with an electric motor but ended up with strange RF signals that were picked up by the ECM, which in turn confused it, so they dropped the project. Then a guy whose name memory fails me at this time came up with a cable-operated manual engagement system and marketed it under the name "Posi-Lok." He has sold it to a company in Coldwater, Michigan, and you can read more about it at For those who drive Dodge trucks, Jeeps, S-10s and even a couple of Ford models with vacuum shifters, there are also Posi-Loks available.

It took Chevy until 1998 to solve the problem. A September, 1998 Technical Service Bulletin # 76-43-01A addresses the problem with a new-style front axle actuator including a new wiring harness kit. To get the proper one from your Chevy dealer, you need the three-letter axle code that starts with a "Z," as there are four different kits. Hopefully, the small metal tag is still attached to the axle by one of the cover bolts.

Between you and me, I think that the Posi-Lok is the better way to go.

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