Full-time 4x4 advantage

Discussion in 'Trucks and Trailers' started by Houlihan, Mar 24, 2001.

  1. Houlihan

    Houlihan LawnSite Member
    Messages: 26

    Hi, some of you guy's seem to really know you're K-Trucks. I'm hoping you might be able to help me out with my research, any info would be greatly appreciated.

    I'm planning on buying a 73-87 K10 LB 350/auto/NP 203 T-case

    I want the full-time 4x4 because of the superior and safer road handling that comes with this system. I currently own a 98 Jeep Grand Cherokee with Select-Trac which gives me the option of full-time, part-time, or 2wd. I leave it in full-time 4x4 since it is very clearly more stable when cornering at speed, and there is little or no difference in fuel economy, just as the manufacturer claims.

    However, I'm hearing that the NP 203 is a real gas guzzler. How bad is it? Are there any other problems with this T-case? does it give the same handling advantages that I get from my Jeep? Or, are there any other full-time systems available to fit the K-Trucks?

  2. reallyrusty

    reallyrusty LawnSite Member
    Messages: 40

    I have a 74 k20 with the np203 case which I converted
    to part time about 2 years ago. I presently get 13mpg on a good day 12 on a bad with sm465 4 speed and 4.10 gears. I drove it for a year before converting the case and the truck did stick to the road like flypaper but the best i ever did for mpg was 10.
    The case is also VERY heavy weighing in at about 170 #s

    hope this helps
  3. Houlihan

    Houlihan LawnSite Member
    Messages: 26

    Thanks for your reply. Yeah 10mpg is very dismal, I could'nt live with that. Doing 20k miles/yr it would cost about $1,500/yr more on gas than what I spend on my Jeep which averages 18mpg. But I'll bet a Chevy K10 could squeeze at least 15mpg with a modern V6, 3.08 final drive in the lighter GM 10-bolts, even with the NP203?
  4. mike reeh

    mike reeh LawnSite Member
    Messages: 229

    yeah i had a swb full time truck with stock sized tires.. it definately stuck to the road.. but gas mileage suffered.. I dont necessarily think its because of the case.. most people over the years have said the coversion for the 203 case does *not* make a significant dent on gas mileage. in other words that would not have been the reason to convert.. saving on drivetrain wear was the main reason...

    i dont think 15mpg would be an unreasonable goal to set if you're putting together a truck, especially with overdrive.. but I dont know if Id even bother with a V6 :) also your choices are limited to less than 73-87 trucks.. it was not offered all those years (the 203). I forget the years exactly, but its well documented, if you do a search (on say, google). you could also not get a 6cyl (I6) in 4wd.. not while the 203 was offered, at least. of course you could put it together, but would it really be worth the $ and trouble for a few mpg? definately your choice, but thats about all I can add.. I definately like the 203 case though..

    good luck-

  5. Alan

    Alan Member
    Messages: 1,185

    I had a '78 K10 with 350/350/230/3.08 and it got 12 mpg. Didn't seem to matter how hard I drove it, it got 12 mpg. Loaded or empty it got 12 mpg. I wish I had it back, I loved the fulltime system and am seriously considering finding another one and bringing the body back from the grave so I can drive it for a few years again.
  6. reallyrusty

    reallyrusty LawnSite Member
    Messages: 40

    Mike is absolutely correct but there is one more thing i would like to add. I don't want to offend any Six cylinder people out there but the whole family of Chevrolet big and small blocks are the best choice for these trucks. There are literally books of parts and knowledge to change the personality of these engines to fit your needs. Anything from low end torque to high end horsepower and at prices that are easier on your wallet than other brands.
    I owned a 292 "6" in a 67 c10 and a 235 "6" in a 57 3600. They were great engines but they were no where near as adaptable as the V-8s.

    Just a thought
  7. Houlihan

    Houlihan LawnSite Member
    Messages: 26

    You were right about the years Mike. I've since learned that 73-79 was the run for NP203's.And you both make a good case for the V8, these trucks are heavy and a '6' would have to work harder than it was designed for. I read somewhere here that an engine is most fuel efficient when it's operating near peak torque. Most of my driving is highway so I guess I need to select a V8 that peaks out somewhere between 2000-3000 RPM. I stumbled across this very useful formula: RPM=(336/tire diameter)x MPH x gear ratio. with the 35" tires I plan on using x 65MPH x (3.08 final drive x 0.70 overdrive)= 1345 RPM!!! Either this formula is bunk! or a 3.08 with 35" tires and an OD tranny aint gonna work. More like 4.10 or 4.56 even, what say you?

  8. reallyrusty

    reallyrusty LawnSite Member
    Messages: 40

    4.10 sounds pretty good to me using your formula
    thats about 1800rpm in overdrive and you still have low range for hauling (thats about 3600rpm in overdrive)

    hope this helps
  9. RTallday

    RTallday LawnSite Member
    Messages: 214

    I hate to be the bearer of bad news, but the OD tranny you speak of is the 700R4. Couple of things here...First, i dont think it was avalable til the early 80s, however im not sure, so if this is the case, you are going to have to swap a tranny and so on if you want to use the 203. Second, if you do get a 700R4, its only a matter of time before you need to rebuild it. They were updated several times on the old units, but they were always a problem. This would mean you have to settle for the good ol TH400 or TH350. I would go for the TH400, cause for the most part, she is bulletproof. It is up to you what to do, but if you want my opinion, here it is. I would go with the NP205 case, its cast iron and gear driven. They are the strongest out there i believe. Also, as Mike Reeh and reallyrusty pointed out, a six just doesnt have enough power. Even if they were offered with 4 wheel drive, just pulling the truck is a chore for the 6 cylinder, ESPECIALLY in 4 wheel drive. Good luck to you and i hope i have helped out a bit.

  10. plowjockey

    plowjockey LawnSite Senior Member
    Messages: 332


    Isn't the 700R4 also computer controlled?


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