Th350 to a np205?

[Magic1]

Ok. So I've got a th350 bolted to a bad np203 and am wanting to swap it for a 205 case. I've found what I need from advanced adapters to make it work but what I want to know is are all the np205 cases that came bolted to a 4 speed gm tranny set up with a 10 spline output shaft?

[Blazin]

SM 465s had 10 spline output until 78, or 79 I believe.
Then they went to if I remember correctly a 32 spline, or the same as a TH400.
TH 350s, and 700R4s are 28 spline if I remember correct.

[Magic1]

Ok. I think I can get the rite adapters regardless of which spline count it has, I was just curious as to how easy it was going to make the process of finding what I need. I'm gonna find the case first I guess and then get whatever adapters I need to fit.

[Jason S]

If you are in an area with wrecking yards that still have these trucks: You may consider, as an alternative to the Advance Adapters route, looking for a factory setup TH350 mated to a NP205. You'd be looking for '80 model trucks as well as '73 and back trucks.

[Magic1]

If you are in an area with wrecking yards that still have these trucks: You may consider, as an alternative to the Advance Adapters route, looking for a factory setup TH350 mated to a NP205. You'd be looking for '80 model trucks as well as '73 and back trucks.

I see you've got two trucks with the 203 case. What do you think about them? Have yours given you many problems? I actually found a 203 case that's been twin sticked for 50$ and the guy said it works fine but I was just gonna get away from that style and go with what's known to be a better one. Is it worth it to just stay with my original tcase or swap it? I've had some friends that have told me that my 203 isn't worth putting any money into but I'm not sure

[Jason S]

Before I get into my usual long winded reply: I would suggest you think about exactly what you want as your end result; Research and consider all your options to reach that result and the cost of such options; then select parts that will achieve the end result within your cost parameters.

That being said:

I see you've got two trucks with the 203 case.

Yes, both trucks ('73 and '74) have the NP203.

Have yours given you many problems?

  No, I have not had any problems out of the NP203 transfer cases. The NP203's in both trucks had been converted to part operation prior to me owning either truck. I have had both trucks for over a decade and change the oil in the T-cases fairly regular and will operate them in 4wd to keep them lubricated.

  I actually found a 203 case that's been twin sticked for 50$ and the guy said it works fine but I was just gonna get away from that style and go with what's known to be a better one.

As with any used parts, I'd say it is "buyer beware."  Are you having any problems out of your current NP203?  For $50.00, you could at least have a spare transfer case for parts and the twin stick setup (if that is what you desire).

Is it worth it to just stay with my original tcase or swap it?

Honestly, that will depend upon what you desire as the final goal.  I have had the '73 GMC with the NP203 (part-time conversion) for about 15 years.  During those 15 years, I put well over 100,000 miles on it with no problems.  Most of the miles were highway miles. However, there have been a lot of miles off-road going places that I probably shouldn't have; pulling 90's Z-71's out of the mud, exploring in Canada, having fun in Texas, etc.    My opinion is that if it is good working order, especially bearings and chain) and regularly maintained, then you shouldn't have any problems.

I've had some friends that have told me that my 203 isn't worth putting any money into but I'm not sure

That decision ultimately depends upon what you want. If rebuilding the NP203 in your truck costs you $400, versus spending $500 to just bolt an NP205 to the TH350, plus any rebuild costs for the NP205, plus an additional $200-400 or more to modify driveshafts, then you may be money ahead keeping the NP203. As for me, I have had many trouble free miles out of my NP203's and don't regret having kept them.

I will say that I neither love the NP203, nor do I hate it.  For what it was designed to do (i.e., full-time 4-wheel drive), it was a particularly good transfer case.  Since most people desire to have a part-time operation option for the transfer case, including me, the NP203 becomes a modified transfer case operating in modes that it was not originally designed to perform.  Due to lack of maintenance, misunderstanding, etc. the NP203 has been derided. While the NP205 is an excellent transfer case, I considered the cost of swapping the NP205 versus keeping the NP203.  In my opinion the primary drawback of the NP203 is that it is extremely heavy. Since mine are both part time converted, I have the 2-Lo feature in addition to the deeper low gearing of the NP203 (versus the 205) and it will do what I try to do with it. In addition to regular maintenance, I have pulled the T-case shifters and completely torn them down for cleaning and greasing and reassembled them. The T-case shifter cleanup (and adjusting the shifter to case linkages) has helped tremendously in shifting the T-case.
 

[Magic1]

That helps a lot buddy. I haven't really found anyone to ask about their experiences with the 203 but have gotten several opinions about them. Mine has been converted to part time and am not real sure what's going on with it. The truck has had the tranny recently rebuilt and new ujoints installed but makes a thunking noise when put into drive. It will go into 2hi neutral and 4 low but when put into high or low lock the truck won't move like its stuck in neutral. That's about as far as I've gotten into it because at the present time I'm working on putting a new engine in it. But that's my next project. As far as my goal for the truck I'm not making a rock crawler or mud bogger out of it. I just want the 4x4 capability when conditions demand it and want it to be reliable. You say yours has been converted also. Do you know which kit was used? I've read that the mile marker kit that replaces the output shaft and basically does away with the differential in it solves a lot of problems. I also see where you compared the deeper low gearing of the 203 to the 205 and if that's the case then that may also be a problem with mine now. When you put it into 4 low it certainly isn't low. You can barely tell it's any lower than the truck would be in drive.

[Jason S]

I'm glad I could help.

I don't know what part time kits went into either of the 203's. The part time kits were in the t-cases before I owned either truck.  They are the type that locks the "differential" in the back of the t-case. Mile Marker kits seem to be the standard kit for part time conversions.

I really like what I have seen about the Mile Marker shaft kit, but last I saw it had been discontinued. I'd say that if you decide to keep the NP203 and find one of the shaft kits, buy it.  I did a quick search and only saw one company listing it, but that doesn't mean they have them... Mile Marker didn't list it on their website.

If you are not getting all ranges when you shift, you may want to first take the shifter apart and clean up everything inside and put fresh grease on the internal parts of the shifter. Once that is done, check the adjustment on the shifter arms. 

A number of things in the driveline, including the pinion could cause the thunking noise. Did the TH350 get a "shift kit" when it was rebuilt?

Whether it is in 2-Lo or 4-Lo, you should definitely get a deep gear reduction. The transmission would shift quickly into 3rd as you drive down the road, you may not notice it so much at slow speeds with an automatic transmission. On the '74 Chevy, while in granny gear and 4-Lo, I can really feel the low gearing.

[Magic1]

Yeah the tranny was beefed up a bit and had a moderate shift kit installed. But like I said earlier I haven't really been able to get into the problems with the case cause the truck has been undrivable with the motor being in the shape it's in. I think I will try cleaning and adjusting the linkage and buy the other case that guy has for 50$. At least that way ill have a spare and save money on adapters/driveline mods. I think the 203 will work for what I'm looking for. Just gotta get it shape.