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700r4 into a CUCV

K

K5dreamer

1/2 ton status
Joined
Mar 14, 2005
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Location
Alexandria, Va
Hey guys and gals. I wanted to ask if anyone had replaced the TH400 in a M1009 CUCV with a 700R4, and if it was as strait forward a process as i seem to think it is.

I have the chance to get a great price on a trans and t-case from a 1988 2500 pickup (mental note, forgot to ask if it was driver or passenger side drop) that has been wrecked. And am strongly considering it but dont know if ill run into any problems. My primary concern is driveshaft length.

The reason for the swap is my TH400 is starting to act up, im pretty sure its a failing pump, but not being a tranny guy, and not having the money to drop the truck off and have a trans tech tear it apart and rebuild it, i dont really know for sure. Also ive been driving it for a long time with these issues and they have been getting worse, so im sure at this point, if its a bad pump, the clutches dont have alot of life left either. So were probably looking at a total rebuild, where the 700R4 in question has less than 1k miles on it.

My truck is a 90% daily driver, and only occasionally sees dirt and mud, but not rocks, and nothing very serious, and its a stock N/A 6.2L diesel, and only has 33in tires, so im not worried about overpowering or abusing the tranny. it may be getting a cheap 4in lift kit sometime in the near future (birthday present) but nothing set in stone.

So if anyone could tell me if i can keep my current driveshafts or not, it would be greatly appriciated. Im pretty sure though that even if i cant use my current driveshafts, i can just find the driveshafts from a mid to late 80's blazer, civilian version with the 700R4 and put those in, right?
 
ok well, at the very least i can probably get the tranny at a good price, and spend the money for the kit from advanced adapters. fit my 32 spline np208 to the 700r4, at least then i know i can keep my current driveshafts and everything. its just gonna cost a few hundred more, still way less than a total rebuild on a th400. the guy wanted 400 for the tranny and tcase from his truck, maybe i can get the tranny for 200 :) rougly 480 for the kit from advanced adaptors, do the swap myself, and spend less then 700 bucks, for better gearing, and overdrive, deeper first gear should improove around town mileage, and overdrive should improove highway mileage.

seems like a worthwhile investment to me.
 
This is just my .02 cents but with stock gearing, 33s, and a possible 4" lift, I would think OD would be pretty much useless on that truck and that would be the only reason to go with the 700R4. Swapping to the 700R4 would likely cost more than just getting your TH400 checked out. If it was a M1008 it might be a different story. That truck definitely needs an OD.
 
Yah, 3.08's + 33's + 6.2L (even with the J-code engine) + 700R4 = trouble.

Good time to consider axle upgrades though.
 
wait, now im confused. the civilian version of the blazer ran the 6.2L and 700R4, why would it be a problem to put the 700R4 behind the 6.2L in my truck??? remember, i dont push my truck, i dont crawl, i dont sledpull, its really mostly a daily driver that i use for camping and trails. i wont deny the 700r4 isnt as strong as the th400, but really the th400 is overkill for my needs. as to the cost, the 700r4 with only 1k miles since a rebuild is gonna cost me $300, and the 27 spline np208 from the local junkyard is $300 with a guarantee. I dont know of any shops in my area that will rebuild a th400 with parts and labor for less than $600.00.

running the numbers the overdrive with 3.08 gears and 33's gives me 1450 rpms at around 60mph on the highway. opposed to the 1880 im getting now. although i certainly wouldnt be opposed to regearing for 3.73 gears in the axles, which would still be around 1750rpm.

so for less money im getting a lower first gear, and an overdrive... but if its not going to survive, i need to know, i just need to know why.
 
well, something else came up to complicate matters. i forgot about the TV cable, and adjustments. i have no idea how to mount or adjust the cable on my diesel, and without that, the tranny will eat itself alive.

guess ill just have to eat the rebuild cost of the th400, and save my pennies for a manual valvebody 4l80e with a np205 adaptor, and some custom driveshafts..... and some 1 ton axles :)
 
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