TH700R4 Tailshaft from 2wd to 4wd?

Hello Everyone,

  Im Back again. My truck is a 1984 Chevrolet K5 Blazer with a 305cid, TH700R4, NP208T-case, Dana44 front and 12bolt rear with 3.73:1 Gears. The truck has currently about 158,000 miles on it.
  Well a few days ago the transmission quit on me, it started shifing rough from 1st to 2nd and then finally nothing at all when I put it into drive. Its like I have two neutrals when I drop it into drive. Well I have another project, a 1983 Trans Am that has a 383 Stroker and a TH700R4. This drivetrain has zero miles on it and has yet to be fired.
  My question is can I replace the 700R4 in my Blazer with the one from the Trans Am? Ive heard about this being done by switching out the output shafts. Have any of you done this before? I would apreciate any info you all may have. If I can swap the tranny I'll swap in the Stroker as well. No use putting a brand new built Tranny behind a tired engine.

Thanks Again all

WarpVelocity9.9  

Sorry, bad idea. There is more to a 4x4 tranny than tail shaft. 4x4 version of 700R4 have a much stronger housing to contain/control counter torque from Tcase bolted to rear of it as it alone keeps Tcase when twisting out and off back of tranny from high counter torque in low range. It is easy to spot these trannies with heavy cases as a few on them made it into 2wd apps too. They have a thick cast and bolted on lower torque converter shield while 2wd trannies have a simple thin stamped one.  

this came from a jeep swap from another site:

I've noticed a trend towards the General Motors automatic transmissions both on the trail and in the extreme rock crawling events put on by ARCA. One of these automatic transmissions, the TH-700R4, is a 4 speed with a 3.06 first gear. By using this transmission, I would have the overdrive for highway use, a decent first gear, and a future swap to a small block motor would be easier.

There is a lot of information available about the 700R4 since it was used in so many different vehicles. I tried to sift through all of it to find out what would be the best donor vehicle. The 700R4 was introduced in 1982 and was used in both cars and trucks. The early versions had some durability issues, but most of those had been take care of by the 1987 model year. The non-computer controlled 700R4s out of V-8 vehicles up to the end of production in 1993 are the most desirable. The transmission came in both 2-wheel and 4-wheel drive versions. Like most GM transmissions the difference is the added tail shaft housing on the 2-wheel drive version.

A rebuilt 700R4 can run quite a bit of money so my goal was to find a core and have it rebuilt. I was lucky enough to have a friend of a friend who is a transmission tech and was willing to rebuild a transmission for a reasonable price. I was unable to locate a 4-wheel drive core, but a local salvage yard had a 1990 Caprice police cruiser equipped with a V-8 and a 700R4. The cruiser was in rough shape but it drove so there wasn't anything major broken in the transmission. I ordered a B&M 700R4 Super Transkit which included pretty much everything to overhaul the transmission and sent it off to the rebuilder.

aparently it does not sound like a big deal. you have the parts allready I would say its possible. sorry this is so long but I thought it had alot of good info. hope this helps. dont mean to disagree with you snoman. I thouhgt from reading this it was possable  

hey i need to get my 700r rebuilt any one have any ideas im in whittier k5 4x4  
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You know I love you all (in a manly non sexual way) Spawn_X

Hey Guys,
  I appreciate the Info. SnoMan, I had no idea there were differences in the case also. Very interesting.
  Any thoughts on getting mine rebuilt or just to purchase a rebuilt unit, like one from Summit Racing, such as their TCI Maximizer 4x4 Transmissions.  

Hey Guys,
 I appreciate the Info. SnoMan, I had no idea there were differences in the case also. Very interesting.
 Any thoughts on getting mine rebuilt or just to purchase a rebuilt unit, like one from Summit Racing, such as their TCI Maximizer 4x4 Transmissions.  

There a few aftermarket builder that make some very serious 700R4 rebuilds. I would look at other than just Summit. A quick google search will reveal a several builders. BTW, if you have oversized tires with your 3.73 gear it is slow death to a 700R4 even with a custom rebuild because the tall OD will ride stall a lot and slow bake tranny. With 33's you should have at least 4.56 and with 35's try 4.88's. Those gear are quite tame cruising with a 700R4 and those tire sizes. Wrong axle ratio for tire size and usage is the leading cause of tranny failures with 700R4's.  

yep its possible to swap the tailshafts but don't do it!!! the tranny won't wisthand all the extra force put on it from the t case hanging off it and all the twisting tourqe it creates....look up on the web bulletproof 700r4 then you will find a seriously built tranny from other than the mainstream ones from summit and such.....and tire size is a crucial factor in your tranny life....if the tires are too big with gears too tall then you will shorten its life unless you regear and put on a good tranny cooler......  
solid axle chevys cant be beat
78 K5: 350 V8,700r4,np208, 8 lug D44 4:88, 14 bolt 10.5 4:88 with detroit locker and 35 inc parenelli jones dirt grip tires

I have an 89 k5 700R4 was rebilt 3year ago when you put it in drive an go it shuders. just started year ago.  
if I shift it my self it dose not shudder. It has a built 350 456gears an 35s 4in lift. any ideas?          

thanks david































i  

Clutches are chattering from wear or low pressure. I know a 4.56 sound low but with 35's and a 700R4 it is really kinda tall and not a good combo.  

Thank you guys for all of your help. I really appreciate it. My 700R4 started to shudder from 1st to 2nd gear and sounded kind of like the tranny of porkchop08.

I'll check out some websites for a seriously built 700R4 since I'm going to drop that stroker from my other project into my Blazer now. It makes no sense to keep a 158,000 mile 305cid with a brand new built Tranny. The 383 Stroker that I have has recently been purchased and has yet to be fired. My dyno sheet shows 490HP and 511 lb-ft of torque. I'll have to now upgrade my axles along with the engine and tranny swap. With the Stroker I know I wont get the great gas mileage of the 305 but with my future plans the 305 wont cut it.

Thanks again and I'll keep you posted.

Good Luck Porkchop08 on your 700R4 Gremlins

Take care guys  

WarpVelocity9.9  

Low pressure im thinkn need to change fluid an filter may help is ther any thing else I can look for to bring up line pressure? truck sat in back yard most of that time waiting on money an parts to build eng an drive train.  i also have brake problems brake light stays on all the time. would like to get rid of c clips an put rear disks brakes on truck.   thanks to all for your help.  

yea thanks on the good luck im probley going to need it they say you play you pay and I love to play cant help it its my dads falt. But why have a 4x4 if your not going to use it. good luck to you on your project 490 hp sweet. An thanks again  

Oh I know that saying well, My K5 will probably be sitting for a while I save up for that new 700R4. Ive been collecting parts such as my lift, gears, etc. I still need to save up for my wheels and tires but hopefully by summmer I'll have my baby back ready for summer palyin. Take care guys and thanks again!
WarpVelocity9.9  

Is the 4L60E ever a suitable option if you need heavy duty trans?