Ok, I have posted in other parts of this forum but haven't updated this to tell what my new plan on the tranny is. After doing a crazy amount of research (more than I care to admit), I decided the allison is really not worth the trouble for me. The tunnel isn't big enough for the allison so floor modifications would be needed, would have to figure out shifters, crossmember modifications, my current 205 would need a new input shaft (the allison is a 29 spline output while I have the 32 spline input 205), redoing shafts front and rear, plus additional costs for a harness job on the tranny too. For what I want, this wasn't really worth it to me.
A 4l80e/4l85e is very doable with less headach then the allison, but with what a tuned 8.1 is going to put out, it would need to be beefed up to handle the power for sure.
Then I had the thought, "What about an NV4500?" I hadn't thought about swapping to a manual, but after doing the research, it will actually be a lot easier for me to do this swap from my current th400 than any of the aboved named options. And I am pretty sure I can make this whole set up a bolt in, while now having a tranny that I am confident will handle the tuned 8.1 power with getting my desired O/D for highway use.
So this is what I have gathered to be able to do the swap: Pick up an NV4500 (pre 1996 model means I could use the bell off a hydro SM465 and drill/tap one or two new wholes in the trans case just to get it to fit, or just use the Adavanced Adapters bell kit which is some money but looks to be a solid kit, or I could use the factory NV4500 bell housing that has external slave on it, but would probably need to lift the truck a few inches to make sure the front shaft clears everything. 1996 and up it sounds like the easiest thing to do is use the Advanced Adapters bell kit since those years are internal slaves and that won't really work with the pedals needed on the truck. I can swap any 85-91 hydro clutch pedal assembly/slave/master/line setup and it should just bolt into my truck (with little modifications) and it will work with either the AA bell kit or the SM465 bell (depending on what yr tranny I find), my round pattern 32 spline 205 will bolt to the back of the gm 4x4 NV4500 with little modifications to the casing to clear the shift rail and a coule other small bolts. The overall length of both trannys (with bell attached) seems to be extremely close, less than an inch off, so I can use my factory crossmemeber and maybe just drill new holes to line it up and driveshafts shouldn't need to be changed (should have enough slip to handle this offage). The NV4500 will bolt up to the 8.1 just fine, just need to get the correct flywheel and a clutch setup. This way I can keep a 100% stand alone harness on the motor and keep everything very simple, and also have availiable replacement OEM parts with whatever I am looking at (motor, tranny, clutch, ect...) as close as the parts store down the road.
Can anyone tell if I am missing something? I am planning to drive to Idaho and meet my brother to pick up the truck next weekend and get it back to CO. So over the next couple months I am going to be gathering all the parts necessary to do both motor/tranny swap and keep it all in my garage. Then when I am ready I will do the entire swap hopefully in a couple weekends.
Anywho, that's my plan now
