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NP203 Exposed

Discussion in 'The Garage' started by CooknwithGas, Sep 30, 2002.

  1. CooknwithGas

    CooknwithGas 1/2 ton status

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    OK, I just solved a mystery. I hope this is helpful to any of you with an NP203. I recently took on a relatively small task of replacing the rubber transmission mounts on my truck. Cheap enough. Didn't look like much work.

    Three weeks have gone by and the new rubber mounts are still in the box.

    While removing one of the two bolts that holds the transfer case adapter to the crossmember where the mount goes, the bolt broke off into the transfer case adapter. I couldn't get the broken fragment out with an extractor, so I had to remove the NP203 and adapter. One week goes by.

    I tried to extract the bolt (now with a broken extractor in it) with NO luck. I find another adapter from a guy on Ebay and get it home. Meanwhile I take a peek inside the NP203 on my garage floor and find some little roller bearings rolling around inside the case. I decide to disect the NP203.

    Another week goes by.

    Now the transfer case is completely dissassembled :

    http://www.cooknwithgas.com/NP203parts.jpg

    I realize right away that I have no idea how this thing works, so I start to study it. After reviewing the exploded view of the NP203 I realize that my NP203 is different and that these little bearings I found have no place in a factory NP203. Here is what the shrapnel looks like:

    http://www.cooknwithgas.com/badbearing.jpg

    It didn't take me long to see other differences with the factory NP203 and mine. Oh, yeah, another week has passed.

    The previous owner apparently installed an aftermarke kit (Nothing like I have heard of here) with a big metal contraption that mates to the output shaft and also required a cheap little thrust bearing to keep it away from the other gear. The bearing was chewed up by the differential gear that it was riding against. (Predictable)

    After studying the problem, I decided to weld the kit part to the output shaft to keep it away from the back diff. gear. This makes it similar to the "shaft" kits I keep reading about here on the board. It will also keep it away from the gear that chewed up the bearing.

    Everything else looks great inside, so I take back all the nasty things I have said about the NP203 and how the part time kit can ruin it due to lack of lubrication. I think this just might work.

    Conclusion - don't install one of those part-time kits that locks the spider gears. This kit also includs the thrust bearing that can get chewed up (see picture above). Go with the shaft kit if you want to convert to part time 2wd. This keeps everything in it's proper place.

    Thanks for all the help I received while looking into this.
     
  2. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Yep that's part of the part time kit. That part time kit blows! Welding it to the output shaft was probably the best thing you could have ever done. You do however need to find another one of those bearings. I'm sure you played 125 pickup with those bearings that the top chain sprocket rode on. That bearing is to keep that Sprocket in line and to keep those bearings from walking out.It looks like it was installed incorrectly because I don't see the second washer it was supose to be sandwiched beteween. It is not supose to be directly against the gear at all. The washer/race is supose to be against the gear.
    If you look at the cross shaft where the hokey part time kit mates too one side of the splies center has a raised area. Well since the partime kit removes the gears that use to maintain the spacing of that to retain the bearing you flip that section over and put the bearing in there to provide the thrust to keep the part time kit in tight contact with the output crown gear as weell as to keep the cage from waliking into the crown gear and the LOC cog
     
  3. CooknwithGas

    CooknwithGas 1/2 ton status

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    Grim:

    Your point about the bearings walking out is Excellent. I hadn't thought of that. A snap-ring would work if I can somehow groove the shaft.

    This is hard to explain, but here's what I did. The aftermarket part that mates to the crown gear is what I welded (See it in the middle of the picture above) It is a full "female" mate to the crown gear - the other side has four slots. No longer any need for the spacer to hold it against the crown gear (it's welded now).

    My next problem is to make sure the round, heavy thing (differential carrier assembly) stays away from the other crown gear. On my carrier assembly all of the gears, bearings, etc. had been removed from the carrier assembly - all there was left was four round posts in the center of the round part (the inner races).

    The aftermarket kit had four slots for these shafts (see it in the picture above in the middle) and that is what transfers the rotational motion from the carrier assembly to the output shaft. The Problem is that the carrier assembly now will hit the inboard crown gear. The cheap thrust bearing was between the carrier assembly and the inboard crown gear. The race to the thrust bearing was destroyed due to the gears - you said there was supposed to be a washer between the gears and the bearing race.

    Here's what I did to keep the carrier assembly from sliding back toward the crown gear - I placed it in the four slots of the part that was welded to the output shaft crown gear. I then took a large washer and cut it in two sort of a half-moon shapes. I placed these on top of the adapter, then welded these washer parts in place. Two of them across from each other. That way, the carrier assembly is trapped in the slots, yet can still wiggle a little for alignment, etc. This way it can't slide back into the crown gear and is forced to stay with the output shaft no matter what.

    Now that you mention it, I do need to do something to prevent the bearings from coming out between the shaft and the hole. Another one of those sleeves may do it, but I don't know how much room there is between the hole and the carrier assembly.

    Thanks for pointing out that to me. I'll try to find something - PVC pipe? It will have no forces acting on it since all of the parts toward the output shaft are constrained and it will only serve to keep the roller bearings from coming out.

    Does any of this make sense to you? Sorry I don't have photos of exactly what I'm describing.

    Thanks for your help.
     
  4. CooknwithGas

    CooknwithGas 1/2 ton status

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    I re-read your post and I see another point you made. When you engage the LOC cog, it slides the whole assembly toward the carrier assembly. If there is nothing there to stop the sliding, it will pull the chain sprocket out of alignment. I see now what you were saying.

    I need something substantial between the carrier assembly and the crown gear to keep the chain sprocket in place when engaging the 4WD. I am assuming the shifter fork will hold it in place when in 2wd correct? Remember, my carrier assembly will not walk back toward the cog cause it is welded in place to the output shaft.

    I don't see why a bearing is needed cause when it is locked, it is all turning together in 4wd. When not locked, the shifter fork should hold it away from the carrier assembly, yes?

    Also, you mentioned you didn't see the other side of the race/washer - look closely. It is inside the bearing retainer in the "badbearing.jpg" picture. It is just eaten away by the crown gears and is much smaller now. There is a little recess in the crown gears and that is where this part was residing after letting all the tiny bearings to escape. This kit may have been installed 20 years ago.
     
  5. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    I still think something was not right with the install Either that or that case was not being put into LOC to get lubrication up to that bearing and it simply fried. Both my trucks have part time kits and both kits use that same (Torgensen?) bearing. Never had a problem with them. I just had my case apart a week ago and it was in purfect shape.
    See normaly that cage and the top chain gear would be turning together. So minimal issues. it was also getting plenty of oil dumped into it from the chain so nothing more than just the edge of the splined section was needed to keep the bearings from walking out. With the part time kits then are alwasy doing something different and need a bearing.
     
  6. CooknwithGas

    CooknwithGas 1/2 ton status

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    I made some modifications to the shaft to solve a few problems. First, I think the "Clunk" is solved with fixing the part-time adapter to the output shaft.

    Last night I used my dremel tool to make a groove on the shaft so I could install a retaining ring (snapring) so the chain gear can't walk toward the output shaft and also to hold the bearings in place. Take a look:

    http://www.cooknwithgas.com/snapring.jpg

    I still don't have the thrust bearing, so I will go by the auto parts store today and see if I can match one up. If not, I may just leave the washer/race from the old one in place and see if that works.

    Thanks Grim for setting me straight on the sprocket alignment. I would have learned the hard way and found out after it was all back together and in the truck.
     
  7. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Well the snap ring may negate the need for the thrust bearing.
    You have the wrong snap ring though. That's and inside snap ring. You need an outside snap ring that will be in full contact with the groove like the one used on on the end of the stub shaft where it connects to the locking hub.
    Let us know how it goes.
     
  8. CooknwithGas

    CooknwithGas 1/2 ton status

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    You are right about the snapring. That was the only one they had that would fit it. I'll try to find an outside snapring when I go in search of a bearing. I still can't find the right size socket for the output shaft, so I have it in my truck and plan to bring it to the autoparts store for a match. The 1-1/2" I bought yesterday didn't fit.
     
  9. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Rear output nut is a 1-5/16 I seem to recall.
     
  10. CooknwithGas

    CooknwithGas 1/2 ton status

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    You recall correctly! 1-5/16 did the trick. I found an extremely chewed up orange speedometer gear. I guess that will be my chore today to find one. What color should I buy for larger tires? (33")
     
  11. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Well the speedo gear also depends on the gear ratio. I would check with a speedo shop (yellow pages). Check the Speedp drive. only what that would get chewed up is if the ouput gear jammed.
     
  12. CooknwithGas

    CooknwithGas 1/2 ton status

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    Yeah, there could be lots of reasons it is all chewed up. I had a little fire that melted the speedo cable a while back (all better now), and also, I'm going to go through the entire output section (now that I got the 1-5/16 nut off). Sandblasted and clear-coated the entire aluminum section last night. Will take it apart soon. The plastic gear is Toast. They don't have them at the Chevy dealer, but they can order one for $5.26, so I'll probably do that.

    It will be spinning free, clean and lubed up before it all goes back in the truck.

    Thanks for your help.
     
  13. weisel

    weisel 1/2 ton status

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    Ok, now I am confused. I am about to put in the part time kit (the crown looking gear one)
    in my 203 and I don't know what you guys are talking about. Why the snap ring? What will
    happen if I just take out the spider gears and put the gear in its place? Why weld it to the
    output shaft? I don't mean to steal the thread, just would like to gain knowledge.
     
  14. CooknwithGas

    CooknwithGas 1/2 ton status

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    Sorry for the confusion. If you install yours according to the instructions, maybe it will last 15 years or so. I doubt you will have the truck 15 years and the next poor guy will have to worry about the POS bearing. In that case, don't sweat it. Mine is probably a real early version of what you have and it was on there a long time.

    Mine had a beefier kit than the spider thing you have. Instead of the small parts you have, it has a round, thick female version of the crown gear that fits completely over the output shaft. It may have been installed incorrectly, but that little, DINKY, POS, (Can you tell I don't like it?) Thrust washer you have in your kit was put on mine between the rear crown gear and the carrier assembly. I don't know if this is the right place, but I think it is.

    Anyway, it self-destructed and left shrapnel all in my case. Remember that this thing may be 20 years old, but comparing it to all the other components in the T-case, it is a piece of junk. I chose to modify mine to make it more like the solid shaft kit by welding the crown thing to the output shaft (I don't think you can do this with the little pieces you have). Since I did that, I need something to stop the part time shaft - the one with the chain sprocket from sliding around - this is what the bearing was for, but it disentigrated. You will see what I mean when you get it all opened up.

    I solved this by putting a groove in the shaft and a snapring in place. It appears to be a good solution to MY problem.

    One more thing. The kit you are putting in may cause a little slop in your driveline. I noticed that mine had a big "clunk" when putting in drive or reverse. Since I welded this thing, the clunk seems to be gone (I can tell because there is no more play in from the front yoke to the back yoke.

    You need to see if there is a lot of play between the front yoke and the rear yoke after you put your kit it. If so, you may have to put some shims in the area where I put the snapring. I have a part number for you for a thrust washer you can buy for $1.95 each from a parts house. It has the right inside diameter for the shaft and is hardened steel.

    Good luck.
     
  15. weisel

    weisel 1/2 ton status

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    I have a round, thick female version of the crown gear that fits completely over the output shaft, but got it out of another 203, so I don't have any instructions. Can I make it work in mine? I don't have the bearing thing that exploded in yours. Where would this bearing go? Does the snap ring eliminate the bearing?
     
  16. CooknwithGas

    CooknwithGas 1/2 ton status

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    It sounds like you are in luck! This is a much better answer than the little peices you got for your kit. Look at my pictures and I'll try to post some more next week (travelling tomorrow and Fri.) You can do the install the same way, but just remove all of the bearings (and gears) from the carrier and install the solid part instead of the little peices. It fits snug with the "cross" part of the carrier after the gears and bearings are removed. You can use the new thrust bearing that came in your kit and don't worry about the snapring if you don't want to. I just think it adds a more sturdy separation between the chain sprocket assembly and the output shaft.

    Let me know how your install goes. You can always re-do it without much trouble cause your t-case is still in the truck. Mine is out and all apart.
     
  17. weisel

    weisel 1/2 ton status

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    Well I'm happy that I have the "good" kit. I don't have a new thrust bearing though. It is not a new kit. Can I use the old one out of the case that the crown gear came out of? Where dose the thrust bearing go? Thanks for helping me out here.
     
  18. CooknwithGas

    CooknwithGas 1/2 ton status

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    I'm not sure about using the old thrust bearing. Mine was toast. The transfer case is all back together now. It wasn't an easy chore. There must be a trick to connecting the shifter linkage between the two cases, but I just had to put it together and blindly catch it in the shifter mechanism.

    You need some kind of spacer between the output shaft and the chain drive shaft after you remove all the spider gears from your t-case to install the kit. You can use the thrust bearing if it is in good shape. I just used a hardened thrust washer and the snapring to keep the chain shaft from moving out of place.

    If you don't put the spacer there, you will have a lot of "slop" in your drive train - something needs to hold the crown gear parts close to the output shaft. Remember from above, Mine is welded. If you have extra parts, you can weld yours to another output shaft and try it. If it gives you trouble, just go back to the original plan of using the other kit you have.

    Take some pictures when you open everything up.

    Good luck.
     
  19. weisel

    weisel 1/2 ton status

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    Thanks. Going to rip into it soon hopefully. I will take pics also.
    Is there a place to get a new thrust berring?
     

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