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full time 4x4

Discussion in 'The Garage' started by drchan, Sep 27, 2002.

  1. drchan

    drchan Registered Member

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    i'm looking at a 75 jimmy and it has full time 4x4. my knowledge is limited on full time 4x4. does anyone have any opinions on the advantages or disadvantages of the full time 4x4 application. if it matters i don't go "wheelin" unless i have to when i'm fishing. any opinions would help.
     
  2. mudhog

    mudhog THEGAME Staff Member Super Moderator

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    put a part time kit in it /forums/images/icons/smile.gif full time 4x4 puts extra wear and tear on the front end and the t-case
     
  3. CooknwithGas

    CooknwithGas 1/2 ton status

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    I recently had this discussion with a long-time transmission rebuilder I happen to know. He really blasted the idea of making an NP203 (I assume that is the full time unit you are referring to) into a part time unit. Especially when using lockout hubs. He said that most of the NP203's that used lockout hubs are TOAST because it gets no lubrication to the bearings when locked out. The chain needs to turn in order to lubricate the hundreds of roller bearings that are in the case.

    It is suggested that you every-so-often lock the hubs in and turn the gears and chain, but according to this rebuilder, it is never enough and you go back to running without lubrication as soon as you unlock the hubs.

    I only asked this question when I removed my NP203 and found lots of little roller bearings rolling around in the bottom of the case. I asked this guy if I should try to find another NP203. He said if I did, it probably had lock-out hubs on the truck and would be equally Toasted on the inside.

    I recommend you go with an NP205 or 208 that has factory part time capability - I'm sure there will be those who disagree with me on this issue, but after looking into my problem, that is my conclusion. Of course drive shafts, transmission adapter and crossmembers have to be adjusted. (new driveshafts and adapters). You can move the crossmember with some frame drilling. Keep reading this board and you will find all sorts of ideas of what to look for.

    Be careful though - make sure you verify all the advise you get here.

    Good luck.
     
  4. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Cookn is dead on. The worst thing you can do to those cases is part time them. If the tires have equal wear then you do not gain much in the conversion. The only time I would recomend converting them is if you running a front locker.
    That said both my trucks are converted. My wifes 79 was converted when we bought it and it's obvious that it has been run long periods without locking it. You can lock it either with the hubs or leave the hubs unlocked and loc the case. Either way works. WHat happens is there is a reservior in the tail housing that feeds a pump that rides next to the speedometer gear. That pushes oil into the tail shaft bearings. THere is also a passage in the output shaft that feeds oil back up to the roller bearings for the top chain gear and the roller bearins where the shaft from the reduction box mates with the tail shaft.
    Cookn...those bearings came out because somebody screwed up and didn't put the part time kit in correctly.
    I'm doing a write up on the 203 and how it works and about both Partime kits Mile marker sells. Should have it out in a few weeks.
     
  5. drchan

    drchan Registered Member

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    ok i'm a novice at this. i guess that if a full time was manufactured then it should be ok to drive on the pavement a bunch. you know, in the city. i'm thinking if something goes wrong it would really be expensive to fix, say in comparison to one that is not a full time 4x4.
     
  6. CooknwithGas

    CooknwithGas 1/2 ton status

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    Grim:

    Do you know what size socket the rear yoke bolt requires? I tried a 1-1/4 and it was not large enough. The front yoke was small 1-1/8 I think. I need to take the rear section apart to see if there is anything rattling around in there also.

    The tiny bearings I found are in the center section where the chian is. I don't know, but I don't suppose this has anything to do with a part time kit. I think there is a problem in the Chain section of the transfer case.

    Thanks for the info. and I'll look forward to reading your article on the part time kits.
     
  7. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    1 5/16 /forums/images/icons/smile.gif Just had mine appart last Sunday.
     
  8. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    If you leave those cases full time the only thing other then chainging the oil that is needed is a new chain every 150k or so. Chain is about $100. With new housing gaskets and new output seals it going to be about $150.
    THe big thing is you have to replace all four tires at the same time and keep them rotated every 5k. If the tires get uneven tread depth front to rear it starts eating at the economy. If you live in a winter climate you will love that case. I have driven mine on ise cover trails and it's very solid feeling. The only case GM ever put in these trucks that was any stronger was the NP205.
    The only thing you want to avoid on dry pavement is putting the Case into the LOC posisiton. Only use LOC on loose surface conditions like dirt, snow or ice.
     
  9. drchan

    drchan Registered Member

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    i'm sorry, i know there is no such thing as a stupid question just stupid people, with that said here is a stupid person question. you say you don't want to drive in the LOC on dry pavement, if it is full time 4x4 it's not already in the LOC position all the time? sorry, my knowledge on this subject is limited.
     
  10. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    The NP203 has a differential in it like an axle. It keeps the drivetrain from binding when turning. The LOC possition on a NP203 locks the Diff in the case so both axles get positive drive even if one axle loses traction just like a locker would put equal power to both wheels on an axle even if one wheel had no traction.
    On pavement you don't want both axles to get the same power when turning. If they did the drivetrain would bind. If you tried to turn then the truck would have to spin tires to ovecome that bind. It would put a lot of stress on parts like front axle u-joints.
     

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