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September 2005 4x4 Tech Questions - Techline

Posted September 1, 2005

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Question: I have an NP205 transfer case from a '79 Ford F-150. Isn't this case supposed to be able to shift from 2-Hi into 4-Hi at speeds up to 50 mph? What would cause the transfer case not to? Would a rebuild be in order?
Trent Moore
via e-mail

Answer: Well kind of, but not always. It depends on the condition of the 'case-they like 30 mph better. You kind of have to back off the throttle a bit until you find a neutral load condition and sort of "feel" the shifter into gear.

Question: I am 15 and own a '98 Jeep Wrangler. I have been reading your magazine for about two years now and think you guys do a great job. I am currently considering swapping in a TBI 383 small-block Chevy, a TH700R4, a Dana 300, and 35-spline Dana 44s front and rear. Do you think the transfer case can handle the power?
Stephen Hooper
via fourwheeler.com

Answer: Shouldn't be a problem at all if you have an easy right foot and don't go super-big on tire size. The Dana 300 is a really nice compact transfer case that is quite strong. I ran one for a lot of years behind a very high-horsepower 383 and a 6:1 ratio four-speed trans without a problem. Do rebuild the case before the install, and in fact if you're worried, Novak Adapters (www.novak-adapt.com) has a shorter-than-stock rear bearing housing that uses a larger-diameter 32-spline output shaft and yoke. They also have a rebuilding kit for the case. An added advantage to the shorter and stronger output shaft is a longer rear driveshaft, which cuts down on driveshaft angularity.

Question: I have a '74 Chevy with a 350ci V-8, Turbo 350 trans, and NP203 transfer case. The trans is only a three-speed, and when I go down the highway, my foot is all the way down to the floor (it gets a couple mpg), and I would like something with more gears.

My buddies told me to go to a TH700R4 because that has an overdrive gear, and I have one sittin' in the back of the garage, but another mud bogger told me that a 700R4 would not hold up in my 3/4-ton off-pavement.

Will the 700R4 bolt onto the adapter plate that's between my 350 trans and 203 'case or should I stick with my "pedal-to-the-metal" trans?

I also have an NP208 'case. Should I just switch my 350 and 203 to the 700R4 and 208?
Chris G.
Michigan

Answer: I would say you need more than an overdrive transmission. It sounds like you need a new engine. It shouldn't take full throttle to cruise down the highway. The first thing to do is to find out just why your motor is lacking power and getting poor fuel mileage. Maybe the engine isn't all that tired but just needs a major tune-up that includes a carburetor rebuild and some ignition reworking.

You also don't say what size tires you are running or the axle gearing. Could it be that you are running something like 39-inch tires and a 3.07:1 axle gear? Matching proper tire size to gear ratio is just as important as transmission choice and engine power.

Once you've solved the engine problems, do consider the transmission swap. The 700R4 is a great trans if properly built, as it has a much lower First gear ratio and an overdrive in Fourth. However, unless you know the history of the transmission, you should take it to a reputable trans shop for a complete rebuild, using all the good aftermarket components (see Jimmy Nylund's story, "Building a Better 700R4" in the May '05 issue for suggestions).

Most likely, it will cost you about $1,200 to $1,500 for a standard rebuild, and more to make it really stand up to hard use with a lot of horsepower and torque going through it. I am sure that you can find cheaper prices on a rebuild, but you just may get a "cheap" rebuild that won't hold up.

No, the adapter for the 350 to the 203 won't fit the 700R4 trans. Your choice is to buy a new adapter, or you will have to use the 208. OK, the 208 isn't as strong as a 205 or the NV241, but I think that it should hold up fine behind even a mildly built 350. You also get the advantage of a lower low-range gear. If you want to use the lockup torque converter, then you have to do some easy modifications to the trans, and this can be done during the rebuild. Summit Racing (www.summitracing.com) offers a kit to handle this modification.

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