What every astro should have had as an option...nice clean install....now where is (as Paul Harvey would say) the rest of the story....
Easy manual shift NP-231C T-case swap How-to
OK, I've been meaning to do this, so here goes....
I found out about this swap on the S-10 forums, and once I heard about it, I couldn't get it out of my mind.... So finally I just did it. Since I already had a completed 233 swap that had been working for years, a logical question is "Why?"
Well, it was precipitated by my electronic shift setup failing once, which honestly wasn't that big a deal, just a loose connection, but somehow that got my mind to chewing on it and one thing led to another..... Once I read about this swap, I just had to find out if it was doable....
Well, it is.....
And it's pretty slick, all the way around. The downside is that the parts are a bit harder to source than the 233 t-case - not by any means unavailable, just less common.
The basis for this swap is the transfer case from 95-97 S-10s and Blazers with manual shifted 4x4. Didn't know they made those? Me either, but it turns out they did, and quite a few of them. It was an option for those buyers who were skeptical of the newfangled electronic shifted system GM was moving into. I found quite a few of them listed on car-part.com and eBay, some with pretty low miles as they were removed from vehicles a while back and are just sitting on shelves waiting for new homes. The listings will most often say "without option F-46, floor shift"... I'm not sure why they specify without F-46 (AWD) but they usually do. The floor shift part is the key. That will get you an NP231 case instead of an NP233. Be careful to double check, though, because there was also an option for a floor shifted auto trans, and I saw at least one listing for the floor shift t-case that was actually out of an electronic shift 4x4 that had the floor shifted tranny....
So on to the case. It's a 231-C that has a splined front output instead of the yoke we usually associate with the 231. It doesn't have a separate designation because New Process just considered it a running change to the same transfer case rather than a new configuration. And it has the same 32 spline rear output as Astros.
![case.jpg]()
![tag.jpg]()
![outputspline.jpg]()
Inside, it's a beefy case with the 1.25 inch chain and a 4-gear planetary.
![caseinside.jpg]()
Outside, it's virtually identical to the NP-233, except just over by where the shift lever is. Here's a picture of them together, the 233 is on top:
![casescompared.jpg]()
To go with it, I got the shifter and cable from a 96 Blazer at Pick'n'Pull. This is what the donor looks like:
![donorinstallation.jpg]()
And here are the parts removed. Basically, there is just a shifter assembly, a cable, and a bracket.
![shiftercomplete.jpg]()
![bracket.jpg]()
I don't see any reason why you couldn't use this case with the shifter from any NP231 equipped vehicle, if you can't find the S-10 shifter setup, though it might take a little fiddling. Because this case is meant to be manually shifted, the tension on the shift mechanism is lighter than the 233 and it has neutral position, which all the factory shifters are set up for.
The GM shifter is nice because it attaches directly and works without any mods, plus it has a built in range switch that gives you your 4LO ground signal for the ECU. If your donor is complete, you can also use this slick range indicator thing that is in the front part of the console:
![indicator.jpg]()
Once you have the parts, you can install this directly, with no more complex fabrication than just using a hole saw.
I found out about this swap on the S-10 forums, and once I heard about it, I couldn't get it out of my mind.... So finally I just did it. Since I already had a completed 233 swap that had been working for years, a logical question is "Why?"
Well, it was precipitated by my electronic shift setup failing once, which honestly wasn't that big a deal, just a loose connection, but somehow that got my mind to chewing on it and one thing led to another..... Once I read about this swap, I just had to find out if it was doable....
Well, it is.....
And it's pretty slick, all the way around. The downside is that the parts are a bit harder to source than the 233 t-case - not by any means unavailable, just less common.
The basis for this swap is the transfer case from 95-97 S-10s and Blazers with manual shifted 4x4. Didn't know they made those? Me either, but it turns out they did, and quite a few of them. It was an option for those buyers who were skeptical of the newfangled electronic shifted system GM was moving into. I found quite a few of them listed on car-part.com and eBay, some with pretty low miles as they were removed from vehicles a while back and are just sitting on shelves waiting for new homes. The listings will most often say "without option F-46, floor shift"... I'm not sure why they specify without F-46 (AWD) but they usually do. The floor shift part is the key. That will get you an NP231 case instead of an NP233. Be careful to double check, though, because there was also an option for a floor shifted auto trans, and I saw at least one listing for the floor shift t-case that was actually out of an electronic shift 4x4 that had the floor shifted tranny....
So on to the case. It's a 231-C that has a splined front output instead of the yoke we usually associate with the 231. It doesn't have a separate designation because New Process just considered it a running change to the same transfer case rather than a new configuration. And it has the same 32 spline rear output as Astros.
Inside, it's a beefy case with the 1.25 inch chain and a 4-gear planetary.
Outside, it's virtually identical to the NP-233, except just over by where the shift lever is. Here's a picture of them together, the 233 is on top:
To go with it, I got the shifter and cable from a 96 Blazer at Pick'n'Pull. This is what the donor looks like:
And here are the parts removed. Basically, there is just a shifter assembly, a cable, and a bracket.
I don't see any reason why you couldn't use this case with the shifter from any NP231 equipped vehicle, if you can't find the S-10 shifter setup, though it might take a little fiddling. Because this case is meant to be manually shifted, the tension on the shift mechanism is lighter than the 233 and it has neutral position, which all the factory shifters are set up for.
The GM shifter is nice because it attaches directly and works without any mods, plus it has a built in range switch that gives you your 4LO ground signal for the ECU. If your donor is complete, you can also use this slick range indicator thing that is in the front part of the console:
Once you have the parts, you can install this directly, with no more complex fabrication than just using a hole saw.
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