November 2006 4x4 Tech Questions - TechlinePosted in How To: Tech Qa on November 1, 2006
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Question: I own an '83 Chevy pickup with 160,000 miles on a 305. It seems to still run well, but it gets terrible fuel mileage. The truck is lifted, with a winch bumper and 33-inch tires with a 3.73:1 gear ratio. Back when fuel was $1.50 a gallon or less, I could live with that, but now that the price has doubled and may stay that way, I am a lot more concerned. I am really thinking of dumping my old tired Quadrajet carburetor and replacing it with something more modern like Edelbrock's Performer carb and intake manifold-or maybe forget the manifold and put on an adapter. Right now I get 11 mpg and hope with the change that I can up it to the 15-17 mpg range. I have about 500 bucks to spend.
Answer: Let's start with the truck first. The combination of lift, winch bumper, and larger tires are part of what's hurting your fuel mileage right now. First, there is the matter of wind resistance and/or what I like to call "dirty air." That winch bumper and the exposed axle and transfer case cause a lot of air disturbance that prevents a smooth airflow under and around the truck. Have you noticed how all the late-model trucks now have wraparound bumpers and low-hanging air spoilers up front? You got it-they want the air to flow smoothly around the truck, not under it. However, even with these changes and electronic fuel-management systems, I get complaints about new 4x4 trucks only getting 14 mpg, or sometimes less. Let's face it-trucks are big ugly boxes that move a lot of air at highway speeds.
The tires add more rolling resistance along with a higher gear ratio, which just may be putting your engine out of its proper rpm range.
As to your carburetor and manifold changes: if you really want to do it right, I would suggest that you hit the wrecking yard and go with a GM throttle-body fuel injection, manifold, and matching distributor, and one of the aftermarket wiring harnesses. A Painless harness is about $300; the wrecking-yard pieces are most likely under $200.
You have a couple of choices in Edelbrock carburetors. While the Performer series works well on the highway and can be had for as little as about $225, I have found through testing that the Thunder series AVS version may be better off-pavement-its price is in the $350 range. A Performer manifold and the gaskets will run you about $185, so you're right into your budget. I am not a real fan of carburetor-to-manifold adapters.
Another carburetor I would consider would be a Holley Off Road Avenger. I have used it with great success, but it's not the best for fuel mileage, and again you would need a manifold change.
Overall, instead of a carb/manifold change, I would consider either having your present carburetor professionally rebuilt, or buying a quality aftermarket rebuild. Jeg's and Summit, for instance, have some remanufactured Quadrajets in the $300 range-right within your budget, with money left over for a nice open-element air filter. Quadrajets work great off-pavement and get probably the best fuel mileage of any carb, due to their small primary venturis. It is something that I would recommend.
The bottom line is I don't think that you will ever reach that 15 to 17 mpg range, but hopefully I am wrong. I ran some figures through my spread sheet and came up with gas at $3 a gallon and a $500 expenditure. To jump from 11 to 13 mpg will take about 12,000 miles before you reach the break-even point, money-wise.
Question: I recently acquired a '75 Ford F-100 4x4. This truck is in fairly good shape for my purposes but for one problem: the steering is shot. It needs all new tie rods, ends, drag links, and so on. I have been unable to locate these parts through Ford, Moog, TRW, Napa, and everywhere else I could think of.
I was wondering about a conversion from another truck that I might be able to do. Ford only made this style of steering system for about 2 1/2 years and no longer has replacement parts. This truck will never see the highway and will only be used around the farm/ranch for work purposes, so I do not want to spend big dollars fixing it. If I can't find something that will work, I will be forced to part it out.
Lacadena, Saskatchewan, Canada
Answer: The first place to look is at Ford Truck Parts (www.7379fordtrucks.com). They specialize in '73-'79 Ford truck parts of all kinds. If they don't have what you need, I am sure that they can direct you to a proper source.
Another place to try would be Sacramento Vintage Ford (www.vintage-ford.com) or LMC Truck (www.lmctruck.com). I would also suggest that you pick up a copy of Hemmings Motor News at your local bookstore. If you're not familiar with it, you should be-it's a monthly publication that is full of ads for all types of vehicles, plus repair parts for sale.
Question: I own an '01 Ford Excursion 4x4. While it is a great truck, the brakes leave a little to be desired with the heavy diesel in front and an automatic transmission.
Can you recommend a product to improve my vehicle's braking performance? I am running the stock wheel diameter. There are a lot of companies advertising rotors, but I don't know what benefit I will get if I do not also replace the calipers.
Answer: There can be a considerable amount of braking performance gained by replacing the rotors with ones with the proper finish and cut-in grooves radiating out from the center to the rotor's edge.
When brakes get really hot, the pads (or the lining on drum brakes) give off a gas that can be trapped between the two friction surfaces. This gas prevents the brake pads from making positive contact and causes what is often referred to as "brake fade." The grooves-or sometimes, holes-release the gas.
A quality friction material can also make a huge difference in braking performance. With some of these performance pads, you may or may not experience some noise or more brake dust, or even the need for more pedal pressure. You could go to larger (and more expensive) rotors, but that would most likely also require new larger-diameter rims and new tires.
You could also consider an exhaust brake. The one I use from BD Power (www.bd-power.com) works great for those steep downgrades with or without a trailer in tow. I sometimes even use mine to save on brakes when getting off the interstate. It's most likely the best accessory I have added to my truck.
Question: I'm trying to find out how you can fit 15-inch wheels on a big-hub Dana 44 (eight-lug) and the GM 14-bolt, because of a much, much better bead than 16.5s. I've been told that you need 3.75- to 4.0-inch backspacing and/or wheel spacers. If so, where can I get wheel spacers?
Answer: It's a really tight clearance issue on several counts. First is the clearance around the calipers. Some people grind the calipers for more clearance, but my thought on this is that if the manufacturer of the calipers wanted them that thick for a reason, they should stay that thick. On the rear, the problem is the size of the drums. Even with about 3.5 inches of backspacing, things are close. It's not only the backspacing, but how the rim's drop center has been designed. Another problem is that the calipers and drums are so close to the wheel rims that they don't cool properly, and in reality transfer a lot of heat to the rim and on to the tire. There is also the problem of not enough clearance for balance weights.
Stockton Wheel (800/395-9433, www.stockton wheel.com) can build a custom set of wheels for your application. I really think that you should consider going to perhaps a 16-inch wheel. There are a lot of tires in various sizes for light trucks offered now in the 16-inch rim size, and there will be more in the future. My guess is that there will come the day when there won't be anywhere near the variety of tires in the 15-inch rim size available.