Where To Write
Address your correspondence to:
Techline
Four Wheeler
6420 Wilshire Blvd.
Los Angeles, CA 90048-5515.
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 or otherwise, we cannot respond to every reader, but we do read everything.
Axle Curiosity
Question: I have an '83 Ford F-350 dualie. What axles are in this truck, and how do you tell the difference? How many splines do they have? I am planning to replace the gears and I would appreciate your opinion on which gears to use.
Trey Jenke
Via the Internet
Answer: Ford offered many options and packages during the '80s, so what I am going to tell you may be wrong, but there is a better chance that it is right. If I'm right, the frontend should be a Dana model 60 and the rearend a Dana model 70. The front has a 9 3/4-inch ring-gear and 1 1/2-inch 35-spline axles. The rear also has the same size axleshafts but the ring-gear measures 10 1/2 inches. You can confirm this by taking a look in the support web of the housing or on the front's top, as there should be a #70 (rear) and a #60 (front) cast into it.
Trim Them Fenders
Question: I have a 1985 fullsize GMC Jimmy. I have already purchased a 6-inch Skyjacker lift for it. I would like to run 38x15x15 tires. Is this enough lift, or am I going to need a body lift as well?
Roger Basso
Prince Rupert, British Columbia, Canada
Answer: According to the folks at Skyjacker, you should be able to run the 38-inchers with just some slight fender trimming. However, a lot depends on the wheel's backspacing and the tire's width. I would suggest that you get the lift installed, then mount up the tires and wheels and see what happens. If you need to add a 2-inch body lift for additional clearance, then you can always cool your hardcore trail rides for a bit while you install the body lift.
Air It Up!
Question: I recently installed a set of BFGoodrich All-Terrain KO tires on my '01 Jeep Wrangler Sport. They are 33-10.50x15s mounted on the stock Jeep 15x8 aluminum wheels. My problem is that in order to obtain a flat footprint, I have to run the tires at 20 psi. This seems awfully low to me for street operation. I would certainly appreciate your opinion and recommendations.
D.A. Anderson
Via the Internet
Answer: That's about right for the air pressure. Perhaps a bit higher, like 22 to 24 psi, would be even better, though at such pressures the footprint might round out at the corners. My guess is that the tires will flatten out a bit after you get a few miles on them. Here are a couple of things that you need to do: Check the temperature of the sidewalls after a good, hard, long, high-speed drive. If the sidewalls feel hot to the touch, then perhaps they're flexing too much and developing heat. In this case you would need to increase the tire pressure, as heat is a tire's worst enemy. Additionally, if the sidewalls flex too much, street handling deteriorates. Then, measure the tread depth across the face of the tire every couple of thousand miles. The wear pattern will give you an idea if you're running too much or too little pressure in them.
Mix Ratios? Don't Do It!
Question: In relation to gearing, I've heard that having a higher ratio in the front and a lower one in the rear will help you out in the mud. Is this true? My '89 3/4-ton Suburban had 3.73s with the stock 31-inch tires. I'm going up to 35-inch tires and was wondering if 4.56s would be good for a daily driver/mud/off-highway truck.
Scott Martin
Via the Internet
Answer: I understand that some mud racers run a different ratio in the front than in the rear. Sometimes this is done to compensate for differences in front-to-rear tire sizes, sometimes they want one end to pull harder than the other to improve handling, and sometimes it is because of the combination of axles used don't allow the ratios to be matched exactly.
Front and rear axle ratios actually have to be pretty darn close to matching-like within a couple of percentage points, at most. It is not uncommon to have a slightly different ratio between the front and rear axle. This can be for several reasons; they came from different manufacturers, such as a Ford-built rearend and a Spicer-built frontend, or because the difference in ring-gear sizes doesn't make for exactly the same ratio, such as a Dana 60 rear with a 9.75-inch ring gear and a Dana 44 up front with a 8.5 ring-gear.
Keep in mind that the front wheels must turn the same speed as the rear when in four-wheel drive, as they are directly connected together by the transfer case. But of course they don't actually turn at exactly the same speed, because of slight variations in tire wear, and also because when the vehicle turns, each of the front tires moves in a different arc from each other, and from the rear, making for a number of different tire speeds. That is why you can't use four-wheel drive on a hard-surfaced road unless your truck's system has some type of differential or slippage unit in the transfer case. Without that, there must be some tire slippage or something will break. Usually it's a driveshaft U-joint but it could be an axle or even a drive gear.
As to your choice of gear ratios, if your truck is mainly used for off-highway excursions, 4.56s will be ideal. Keep in mind that it will put the engine rpm at approximately 3,000 rpm at 65 mph.
What's In The Locker?
Question: I know that automatic lockers, such as a Detroit, will make your vehicle handle differently on the road, and can reduce tire-tread life. If you have manual locking hubs in the front axle with, say, a Detroit, will those same problems exist if the hubs are unlocked?
Nick Gerbino
Via the Internet
Answer: What you need to keep in mind, Nick, is that when you put the hubs in the unlocked or "free" position, you are disconnecting the wheel assembly from the axleshaft. This allows the wheel to rotate freely on the spindle without driving the axleshaft, which in turn is connected to the differential, locker or otherwise. If you put the transfer case in four-wheel drive with the hubs in the free position, power goes to the differential and on to the axleshafts but the shafts just turn within the unlocked hub. So as you can see, there is no problem on the highway using a Detroit Locker in the frontend of a part-time four-wheel-drive system. In fact, with the new Soft Locker, I often leave my hubs locked in but the transfer case in two-wheel drive on the street with little change in driving feel.
However, I do caution anyone about driving with a front Detroit Locker in four-wheel drive at above-trail speeds as there are some handling differences. In fact, a Detroit Locker in the rear alone will often unload when coasting out of a turn and cause a jerk to one side or the other. In icy road conditions this can lead to a spin-out. I speak from experience as this has happened to me on several occasions over the 20-year period that I have used Detroit Lockers.
There also will be instances where you can't turn quite as sharp in a tight turn. However, this hasn't kept me from installing Detroits in just about every 4x4 I have ever owned. If you plan to use your four-wheel-drive capabilities on snowy roads, then I suggest that you use the Truetrac differential up front instead, as it is a lot more forgiving.
Torsion-Bar Lift
Question: I have a 2000 GMC Sierra 4x4 extended cab with the 5.3L engine, automatic transmission, locking rear differential, and trailer package. I'd like to gain a little more clearance (1 to 2 inches). Can this be accomplished by adjusting/replacing the torsion bars?
Craig Breckenridge
Via the Internet
Answer: This is a question we get asked several times each month. You can gain some additional height by adjusting your truck's torsion bars, but remember, any time you get more downward wheel travel by either using a stronger torsion bar or putting more tension on the bar, you're reducing the amount of wheel travel available in the other direction. This makes for not only a stiffer ride but the reduced travel can hinder off-road performance by holding the tire in the air. If the tire isn't on the ground, it doesn't grip very well.
