203 trans case in 2 wheel drive

bill rogers

Junior Member
am putting 454 with th400 tranny in 81 2 wheel drive blazer for hunting rig and trailer puller have 203 transfer case with 27 tooth spline input .dose th400 have 27 tooth spline output that will mate up I can built the adaptor has anyone done this .will give me extra low for mt. trailering.. Bill......


i am not sure i completely understand what you are talking about, but, I have a th400 with a np203, the np 203 was only built one way so it will mate up with a th400, i dont know which adapter plate you need but, I know that they are around.<p>-abe??


Junior Member
You need a conversion kit for your 203. Mile marker makes 2 kinds. You need this because its not good to run the case in lock constantly.


Bill,<p>Sounds like you are trying to make your own gear reduction, or &quot;underdrive&quot; unit. There are many on the market. I know they are expensive, and understand you already have the NP 203. For any adapter you could possibly need, check out Advance Adapters. You'd ant the part time conversion kit fit it though. By installing it, you'd actually get an extra gear, when in 2wd, so to speak.<p>www.advanceadapters.com<p>~Chuck<p>----------<br>Chuck's Chevy Truck Pages - Snowplowing Central<br>http://members.aol.com/csmith669/plowcentral.html

bill rogers

Junior Member
yea ,chuck thats what i'm after an underdrive as I pull both fire wood and travel trailer in the coastal mountains here in oregon and its murder on transmissions . I have a good strong 454 and rebuilt 400 and np 203 so just figuring how to put them all together , am also doing a frame up on 73 3/4 4x4 with lots of rust. bill.......