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Full time and part time 4wd

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by codeman, Aug 20, 2002.

  1. codeman

    codeman Registered Member

    May 8, 2002
    Likes Received:
    Lincoln, Nebraska
    I have read a lot about full time 4wd. I have an '89 Blazer with a NP241 Transfer Case and manual hubs. Will I ruin anything if I drive on the street with it in 4wd? And what makes a full time 4wd transfer case different from the NP241?
  2. dremu

    dremu Officious Thread Derailer Premium Member

    Feb 27, 2000
    Likes Received:
    East of San Francisco
    What makes a full-time case different is the center differential, which allows the front and rear to spin at different speeds (which they do when you're turning). On flat ground pointed straight ahead, all four wheels spin at the same speed, but when turning, the outer set of wheels go over more ground than the inside set.

    Now, there are differentials on each end to allow the side-to-side variation necessary to steer on the road, on both full and part time.

    Anyway, your part-time case is either 2WD, where the front axle isn't driven at all, or 4WD, where the front and rear are locked together. The front wheels won't spin unless you lock the hubs, but the front axle will spin anyway.

    It is not recommend that you lock the hubs and run in 4WD on dry pavement -- the locked system won't allow for that natural difference in spin, in turns as above, and ... something has to go. Hopefully it's just tires, but on dry pavement you have good traction, so you'll stress the drivetrain. In the long-term, bad.

    Some folks drive with the hubs locked and just pop the t-case in and out of 4WD. This means your half shafts up front are always turning, which will in turn spin the front driveshaft, but the t-case won't be connected to it. Advantage here is not having to get out and lock the hubs; disadvantage is increased wear on the front axle.

    My only truck with a t-case like yours is my Burb, which doesn't go off-road. I switched out the auto hubs for manual 'cuz I distrusted the autos, but other than that, I am OK with hopping out, locking the hubs, and shifting the t-case on the few times I'll need it.

    Both my Blazers are converted full-times (NP-203's) with manual hubs as well. The Chalet stays in 2WD unlocked for least wear and maximum fuel economy -- I mean, who's gonna mud-drag or rock-crawl in a Chalet?

    The regular Blazer spends wintertime with the hubs locked 'cuz I'm lazy and don't mind a little extra noise and drag, so then I just pop her into N, slam the t-case level forward and I can get out of the driveway (gets muddy enough to slick up my street tires in 2Hi! ;-)

    I am debating un-converting it back to full-time so I have the center diff.

    Hope this helps.
  3. 79Silv4x4

    79Silv4x4 Registered Member

    Aug 14, 2002
    Likes Received:
    Lawton, OK
    Out of curiosity, why would want to drive on the street in 4wd?

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