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NP203 transfer case oil pump

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Leadfoot, Jun 6, 2002.

  1. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    In the Mile Marker conversion kit install article on www.offroad.com they say quote <blockquote><font class="small">In reply to:</font><hr>

    Before you install the MileMarker kit, we recommend you have the follow tools, and parts on hand: Sockets up to 1-1/2", NP203 plastic oil pump gear (GM PN 11801), RTV silicon sealer and a torque wrench. This will save you considerable frustration and having to run the dealer or the auto parts store in the middle

    <hr></blockquote> but when I called GM they have no listing for 11801 and don't have anything listed as an oil pump for an NP203. Can anyone give me a description of this part or the true GM part number?

    P.S. Is Shawn still the contact for the tech articles on the offroad website?

    Thanks in advance
     
  2. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    I've already tried more than once to contact Shawn about those articles being screwed up/missing. He no longer responds to emails or PMs on CK5 or ORC accounts. Steve Fox posted recently that (IIRC and paraphrasing) he had put 4x4 stuff on the back burner and was working on race/muscle cars or something of the sort...

    About the 203 oil pump, seems like it has an oil slinger/pump. After putting in the part time kit, I've seen statements that you must put it in 4x4 periodically for it to properly oil. That's all I can contribute...
     
  3. Redfrog

    Redfrog 1/2 ton status

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    I rebuilt my 203 last winter and used a shaft kit. GM does still carry the gear I will see if I can find the # for you. on the old shaft the gear was metal, the new one will be plastic...

    let me look I should still have the reciept
     
  4. Redfrog

    Redfrog 1/2 ton status

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    the new Part # is 376176 from the dealer that I called to get the # it costs $12.00 I looked it up at http://www.gmpartsdirect.com and it says it's $3.00
    Hope this helps
     
  5. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Dude, you are the man! I called my buddy at the local GM and that is the P/N. When I called the first time and gave them the 11801 number they couldn't find it, and thought it might be the 376176 but not sure. Again thanks for the confirmation! This site rocks.
     
  6. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    It's in the tail shaft next to the Speedo drive gear on the tail shaft. It looks simular to a speedo drive infact but it's about a 1/4 the width. I have had several of these cases apart and I have as yet to break one. Best thing to do is take the the yoke off the tail shaft housing. Take the last section of the housing off. The speedo drive gear will be clearly visiable and the pump will be right behind it in a machined hole. In the remaining part of the case. Also pay attentiuon to where the factory end play shims are in that tail shaft area. That's where the new shims that come with the MM kit also go.
    When you go to remove the larger section of the tail shaft housing push the exposed tail shaft in towards the tranny so that it stays with the case as you remove the rest of the tail housing. It will have enough shaft engagement that it will hang there no problem as long as the truck is nose down a little. THere are a bunch of roller bearings where the tail shaft joins the diff section. Stuff some paper towel in the open hole into the chain housing so they cant possibly fall into the case. Put you hand under the diff and watch where the shafts come apart. that's where the bearings will be falling from so catch them. Some axle grease will hold them in plase when you reinstall.
    Whatever you do do not spin the the chain while the case is appart. THere are 120 or so more roller bearings under the chains top gear and a thrust washer on the diff keeps them from coming out. That trust washer will come out with the tail shaft assembly. There will be a new thrust bearing (torgenson I think is the name) that will come with the MM kit that will be installed there.
    The job is not that bad. The thing to watch out for is some of the early cases made 73-74 there is a clearence issue in the housing and MM does not recomend using the cheaper kit with the tabs. They recomend the better kit that replaces the whole shaft. It doesn't have the interference problem. Be sure to sheck the end play in the tail shaft. Tighter is better. Add shims till it's only got about 1-2 thousandths end play. That is not very much at all. You could jest feel the shaft move a hair. Probably couldn't tell with your eyes that it had moved. If it has to much play the tabs on the kit can tun sideways and cause unusual wear or possbly allow some extra slop in the drive train that might become apparnet with a clunk when you drop it in gear. Well if your chain is worn your probably use to the clunk /forums/images/icons/smile.gif
    Now these cases run MOTOR OIL. Gear oil is too thick and Gear oil is what probably breaks the oil pump. OVER FILL THE CASE after you install the kit. Get the rear wheels up on a ramp and fill that sucker till it pours out the fill hole. What this will accomplish is you will notice the big section of the tail hoising has a lip. That lip forms a resivior to supply oil to that pump. The resivior gets filled by oil slinging off the chain. Well the chain isn't turning any more. So every couple hundred miles (and you need to do this right away after you install the kit) you need to throw it in high lock with the front hubs unlocked and drive it for a few miles like that. That will get the resivior refilled. Over filling the case will alow some oil to slosh over the lip and make it less likely that the pump runs out of oil.
    If you take a close look at that tail shaft when it's out you will notice it has a hole down the center. Well that pump also moves oil up to those bearings that fell out when you took it apart and the bearings in the top chain gear are also fed oil by that pump.
    Part time kit is the worst thing you can do to a 203. That said.... both my trucks are converted /forums/images/icons/smile.gif
     
  7. Redfrog

    Redfrog 1/2 ton status

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    were can the shims be bought? when I tore mine down they were gone(in little pieces) and where do they go? I don't have much slop but I don't like the idea of a $230 shaft going sought when it could be prevented...
     
  8. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Most large towns have a shop that rebuilds Manual transmissions and transfer cases. They will have them. The place I use in Atlanta is called Southern Gear. They use to have a web site but the URL no longer works. They sell a whole gasket set for a 203 (not including the input and output seals) for $5 last time I needed a set. Pep girls gets $40. Look in your local yellow pages under Gears. That's where it was located in mine. also try transmissions.
     
  9. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Sweet thanks Grim.
    I picked up this truck about 4 months ago (another to add to the "K" series collection /forums/images/icons/smile.gif). It already had the cheaper MM kit and has 80K+ on it and it has developed some slop (when going forward to reverse, I checked R&amp;P and put new u-joints in) so I am going to put the MM kit that has the replacement shaft. I have worked on several NP205 but have very little experience with the 203 (other than installing and removing whole cases, never got into the insides). Thanks for all the heads ups, I will need them.
     

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