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October 2002 4x4 Truck Repair Questions - Tech Line

Posted in How To: Tech Qa on October 1, 2002
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Address your correspondence to:
Techline
Four Wheeler
6420 Wilshire Blvd.
Los Angeles, CA 90048-5515.

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More Jump For A Jeep J-10
Question: I recently bought an '83 J-10 from the Nevada State Survey Crew, with the 360 V-8, no rust and just 76,000 miles showing on its odometer. The only thing wrong with it is that its oil pump went out. I'd like to replace it with a modern, more efficient six-cylinder engine and am looking for the most compatible swap.
Ross Erickson
via fourwheeler.com

Answer: Sure, the 360 isn't the most economical engine, but you have to take into consideration the Jeep pickup is like a brick going through the air when it comes to aerodynamics. Just how much better fuel mileage do you expect to get?

You're going to be money ahead in the long run if you just rebuild your present 360 or find another 360 to replace it with. As for a six-cylinder engine replacement, you have a couple of choices: Install an AMC six, which will bolt up to your present transmission; or adapt another brand. Add up the cost of an adapter to the transmission, the new engine, reworking the electrical system, relocating and modifying the radiator, building motor mounts plus the time involved. Now figure just how long it is going to take to pay back that investment. Seems like an easy choice.

Transfer Cases For The Uninitiated
Question: Here are some questions about transfer cases that probably are simple to you, but are way confusing to me:
What is meant by a "divorced" transfer case?
How do you "double-up" on transfer cases? Why? (i.e. TTC Challenger #7 lists a NP203/NP205 for its transfer case.)
What are twin sticks and why do people get them?
What is a slip-yoke eliminator?

And also some transmission and differential questions:
What does TTC Challenger #25 mean by "with Chelsea 350 directional PTO?"
What is a "Lincoln Locker?" Are there any benefits to having one of these?
What/Why/How on "welded gears."
What does "Lock-Right" mean?
Bruce Redmon
Kodiak, Alaska

Answer: These sound like good, reasonable questions to me. Let's start out with the divorced transfer case. To divorce is to separate. The transfer case and the transmission usually are coupled as one. There was a time when the transfer case was a separate gearbox that was connected to the transmission by a short driveshaft. This is still the case on some heavy AWD trucks. By directly mounting the transfer case to the transmission one less mounting crossmember is needed, thus the extra driveshaft with its slip-yoke and two U-joints are eliminated. Besides that, the rear driveshaft length is now longer for less angularity. I use divorced cases because doing so allows you to add a transfer case without having to buy an adapter-which is helpful when you choose an odd transmission, or when you're converting from 4x2 to 4x4. It isn't something I would recommend doing.

Doubling-up a pair of transfer cases is actually mounting two transfer cases together. The advantage is that you multiply the overall gearing again by the ratio in the second transfer case. For instance, both the NP203 and the NP205 transfer cases have a low-range ratio of about 2:1. Now with two transfer cases back to back, you can run one in high range and the other in low range for a 2:1 gear ratio, and by shifting the second one into low range, you can also have a 4:1 gear ratio. By using a 203 and a 205 you can also have a full-time system with differential action when needed, or a locked-up part-time system. The added length can be a deterrent for acceptable rear driveline angle unless it is in a long-wheelbase vehicle like a pickup. And no, you just can't bolt the two together; it takes some special machine work and a special adapter.

Twin sticks are nothing more than two shift levers that independently select four-wheel-drive engagement and low range. Sometimes internal modifications are made to the transfer case so that low range can be engaged while in two-wheel drive. Sometimes it's done so that one stick controls low and high range for the front axle and the other low and high range for the rear axle. Naturally, you can't put one axle in high and the other in low, so you have to actually think about what you're doing. Why would you want this? You'd want it so that you can disengage the rear axle and pull with the front if you have a spool or a Detroit Locker in the rear and you want to make an extremely tight turn (spools and lockers have a tendency to push the front tires instead of letting them turn).

As for the slip-yoke eliminator, as an axle goes up and down, the length of the driveshaft changes. To make up for this constantly changing length, a slip-yoke is installed within the driveshaft itself. To cut costs and simplify manufacturing, almost all of the new transfer cases use a slip-yoke attached to the driveshaft that slides into the transfer case's output shaft. If you should have to take the driveshaft out, the fluid will leak out the end of the transfer case as there is a seal that the slip-yoke slides into that prevents this when the shaft is in place. A major benefit on Jeep vehicles is that a new output shaft and bearing housing is used which shortens the overall length of the transfer case by approximately 4 inches. This translates into a 4-inch-longer rear driveshaft, which greatly eliminates some of the driveline angle, especially on lifted vehicles.

To is the abbreviation for "power take-off." This is a special gearbox that mounts to either the transfer case or the transmission, and provides power to a separate driveshaft that is used to drive some type of an accessory, such as a winch. Not all transmissions or transfer cases have this provision.

A "Lincoln Locker" is the same thing as "welded gears." That's when the differential's gears are welded solid and can no longer function. The axleshafts are now connected directly together so that both wheels will drive at all times. This is a cheap replacement for a locking differential. Whenever a turn is made, one wheel will have to slip and skid. I don't recommend doing this, especially on a street-driven vehicle, as this arrangement will promote unpredictable handling and excessive tire wear, and there is always the possibility of the weld breaking and damaging the ring-and-pinion gears and the bearings.

Lock-Right is a trade name for a specialized differential kit that can be installed in an open differential to convert it into a mechanical locking differential.

Hope this clears things up for you.

Shafts And Ratios
Question: I own a '92 Ford F-250 Extended Cab 4WD with a stock 460 V-8 and a five-speed stick and a 1011/44-inch rearend. I've been thinking of installing a 6-inch suspension lift and a 2- or 3-inch body lift to accommodate 36- to 38-inch Super Swamper TSLs. If I do install this lift, will I have to move my rearend forward to compensate for the lift or get a new driveshaft made? Would I have to change from the stock 3.73:1 ratio to maybe a 4.10? If you can give me any guidance that would be a big help.
Brian Safick
Thompson, Ohio

Answer: Most likely, a 6-inch lift will require longer driveshafts front and rear. You just can't move the rear axle forward. Doing so would require all new spring mounts. Also, you would move the wheels so far forward in the wheelwells that there wouldn't be enough room for the larger tires.

As to gear ratio, I would suggest a 4.56:1 ratio. Let's just say your present tires are 32 inches tall. In direct gear, not Overdrive, the engine speed would be about 2,375 rpm at 60 mph. Going with a 4.11 ratio and 38-inch tires, the engine speed would be only be 2,150. The 4.56 ratio would put the engine speed at 2,425. While that is a bit more than it was originally, it actually will be better because the larger tires will have more drag and the lift kit will set the truck higher, thus exposing more driveline components resulting in more drag. The higher rpm will put the engine in a better torque range, especially in Overdrive, to handle this extra drag.

Bolt It In
Question: Can you point me in the direction to install a Dana 60 in place of a Dana 44 on a '74 Blazer? What problems will I have?
Jonas Smith
Los Angeles, CA

Answer: This is almost a bolt-in, but because the D60 has larger-diameter axletubes than the D44, you will have to use U-bolts and plates that accommodate the D60. You also will need to have the driveshaft shortened, as the larger centersection moves the pinion yoke rearward. You may also have to change the pinion yoke out to the 44 style or change the end on your driveshaft, as most likely the 60 uses a 1350 U-joint instead of the 1310 series.

There is a larger problem, however. Unless you're going to go with one of the aftermarket rearends, the 60 has an eight-bolt wheel pattern and your Blazer has a 6-bolt wheel pattern and this assumes that you're putting the D60 in the rear. Or do I assume that you have already changed the rearend to a 60 or Corporate 14-bolt, and are considering this swap for your Blazer's front axle? In any case, don't forget that you have to match front and rear gear ratios.

See Our Website!
Want your tech questions answered on the Internet? Is so, just log onto www.fourwheeler.com and click on "Text Exchange" to get the scoop from readers with the same problems you have. It won't cost you a nickel.

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