NP203 carriers

[zac]

I got my Mile Marker 501 part-time conversion, be a couple weeks before I have time to install it. The instructions mention this kit is best used with the cast iron carrier as opposed to the stamped steel one. I've read about this before, my question is how would I know which one I have without pulling the tailhousing off the case? The case I'm using supposedly came out of a '79 K20 and it has a th400. My truck is a '79 K20 camper special with full floater. It would make sense if it had the heavy duty part, but I seriously doubt it's that simple. I have my old 203 and I will pull it apart before I tear into the good one. But the problem will be if I don't have the cast iron carrier in either, now my truck is disabled. I could run the steel one, but it would bug me to know it isn't how I want it. Is there some year range the cast iron carrier was used, or is it entirely random? I'm afraid it's like 4 bolt mains, you only know when you see them.

I would also appreciate any tips on other problem areas I might want to inspect when things are opened up. I will do an oil change as well. Thanks.

[LONGHAIR]

I wouldn't worry about it, which is exactly what I say about 4-bolt mains too...essentially for the same reason too.
The "weak-point" of the carrier section is not the main "ring" itself, it is the teeth that engage the chain mechanism. So the heavier carrier does no real good. Either works, but I would hold on to one for a back-up. Those inner teeth are far more of an issue than the ring itself.

[zac]

I agree. I've spent too much time worrying about this parts chaser/work truck, I've got more interesting projects to worry about.

I pulled apart the old 203 just to have a look. It has the steel carrier (when I actually read the instructions it said the cast 2 piece was 73-77). When I drove my truck home with that t-case installed, the truck was barely functional, the entire drivetrain has been replaced since. I remember wondering if it had the part time conversion, but everything was such a mess and the mechanical work so poor that I just ripped everything out and never thought about it again. So I was surprised when I pulled it apart this morning and the spider gears that Mile Marker said would be in there weren't. No wedges, either. Just this toothed ring in their place (made in Brazil). So I assume this is a different, older type conversion. When I dug deeper I found that flat bearing installed, just like the one in the MM kit (but different diameter for some reason), but all the rollers are gone. It's the one on the left in the picture. Also, instead of the 15 roller bearings that were supposed to be in the inside of the output shaft, I got 14. I counted several times, and I didn't drop any. You can see lots of shrapnel on the right in the other picture.

I was wondering if the bad engagement teeth you were talking about Longhair are the widely spaced ones on the outside in the second picture, the ones that engage the teeth on the carrier? That setup didn't impress me.

Is there any reason to try and salvage this part time kit? Were they any better or worse than the others--at least when installed correctly? Right now I'm thinking I'll just install the new kit in my good case and forget about this mess.

[LONGHAIR]

The teeth of the ring gear itself are the potential weak link, but it usually comes from "contact" with the mating gear. That happens when the torrington bearing fails.....the whole thing can get ugly, if that happens.

As far as the needle bearings, I'm pretty sure that 15 is correct. Maybe the last person in there lost it? If you place them around the inside of the cavity where they belong , they fit very closely. The last one has to "slide in" from the end, it will not push in from the side. A little bit of grease will help them stay in place until the last one goes in, at that point they are somewhat trapped and will not fall out.

There is nothing wrong with the kit you have. I have installed hundreds of them with very few issues. There were a few that failed, mostly because of the owner/driver. Lubrication is very important to these converted 'cases.

[74chevy4x4]

Longhair is correct, I believe. I did the conversion this summer and it worked out great. Mine was a text book conversion and it now has the blocks. I just did another upgrade, swapping the TH350 for a 700R4 and the NP203 for an NP208. I am looking for a new owner(no it's not for sale, I just don't need it anymore) for the NP 203 if you are interested. I see you aren't too far away. Let me know.