i have 87 blazer with bad tranny i have a 91 two wheel drive chevy with good tranny that i would like to swap into blazer both are 700r4 my question is do i have to disassemble the whole tranny to change tail shafts and does anyone know of good manuals to walk a person through a rebuild of these transmissions i would like to rebuild the one that i am going to pull out of blazer for spare  

Forget this idea unless you plan to completely gut 87 case and put 91 parts in it. The cases are thicker and stronger on 4x4 trannies to control Tcase counter torque in low range. It is easy to spot a heavy cased tranny. It has a cast bolt on lower torque converter cover, LD case is stamped steel.  

changing the shaft and using the 87 case is fairly easy, you don't need to dissasemble the drums, pistons or remove the valve body. only pull a few retaining rings, thrust washers, reverse clutches and the governor so the gear doesn't get broken.

as far as that goes, unless the reverse is out on the 87 you don't need to go beyond the center support to fix the 87 with the 91 drums.

be sure to flush the cooler lines and convertor.  

thanks alot guys sounds like from what i am understanding that i can use all the stuff out of two wheel drive one and put in four wheel one right if i do this should i use the two wheel converter also i traded for this from a buddy and was there when tranny went out it is no good at all no gears would like to have it redone just cant afford it right now and i have this other tranny that is good just trying to get one together to ride this winter thanks for the help  

Do not underestimate the need for the stronger tranny case design. Some might get by but the ONLY thing that keeps Tcase when twisting out of truck in low range is tranny which transfer this to engine and engine mounts, nothing else. When you make 2 or 3000 ft lbs of drive shaft torque that means there is about 2 or 3000 ft lbs of counter torque trying to twist Tcase off. Especially if you are one of the big tires and tall gears guys as many never consider the impact of counter torque or driveline torque. You will have a very bad day if you use a 2wd tranny case and break/twist it off.  

thanks again for info i only running 36s with 513 gears so not to much stress but i am going to find a way to use the stronger case one way or another didnt know till today there was any difference i have about three of these laying around so i will use what i can to put one good one together again thanks alot  

here's a 2wd th400 that was mated to a 205 t-case..

the conditions of the bell getting busted were a little extreme, I should add....

 

i am definetly convinced!!!!! heavier case for sure but i bet what ever caused that was awesome  

lol, yeah, it was a 427bbc negotiating 39.5" swampers on a hill climb, it did last for two years tho, mostly daily driven, then I got the notion to play go play with a jeep.  

You should warn us before posting graphic images! My kid gets on here for Pete's sake!  

omg thats bad @ss  

well mudb8 did you make it up the hill before it came from together!!!  

yep, a few times, just not the last time!  

what you use that for now Mud, a paper weight? If you also lean toward th400, not only make sure you get the 4x4 case, try and find a th425,450, or 475. They're have heavier planetaries tha their th400 little brother. You can find them in alot of military K5's and even some civilian models. You can also find them in delivery vans and bread trucks.  

well, its just a core with good parts in it now.

the 425 is a frontwheel drive 66-79, not all the 475's have the heavy straight cut low gear planetaries, they are the same standard 32 spline th400 with a heavy case and some have a bolt on yolk and a drum e-brake mounted on em, started in 71'. the th400 was born in 64'
the 450 is basicly something guys dreamed up for what they call a beefed th400. down the line the 375 is a 2wd th 400 from 72-76 with 1 less friction in the drums and has a long output shaft the same 27 spline count and diameter as the th350 which some also call a beefed up th350 a 375. theres alot of confusion on the matter from people who just don't know.  basicly if ya run across a dude with a fullsize thats bragging about having a 450 tranny laugh it up and pass it by unless they can produce a reciept for the straight cut planetaries or you think ya can tell the difference by how it feels in first gear, cuz it's a joke and prolly got abused badly and has a gear hamering shift kit in it, don't buy it expecting it to live long.

the diesel blazers and trucks have deep pan/heavy case th400s, none of em ever saw a low gear planetary set, motorcoaches, box vans, and busses are where to find a th475 gear set.