Need help determining if this 700r4 will work for my set up

[conoco]

My truck
1972/k2500/th350/np205

There is a guy in my home town that is selling a 700r4 for $600. I am going to go look at it this week because those are few and far between where I am at. It is currently matted to a 1984 suburban and also to a np208.

My question is will this 700r4 mate to my np205? I understand the splines might be different. I just figured even if I had to buy some parts/adapters to make it work it would still be well under the gearvendors unit.

I know there are also some variables that I might need to work around. My understanding is the 6 inch tail th350 the 700r4 will swap right over and the short tail will need 2 or 3 inches cut off the drive line. I will measure mine when I get home but I am pretty sure its the short tail. I am just wondering if someone could let me know everything I would need to make this work. I don't want to waste this guys time or mine. I am all for buying the parts to make it work but I guess it all the depends on the modifications that would need to be done. If it gets to crazy ill just keep the th350 and get the gear vendors. Thanks everyone.

[57taskforce]

I’ll probably get flamed for saying this, I wouldn’t touch it. The turbo 350 is stronger and more reliable. I said it already in another thread earlier today. They don’t belong in a 3/4-1ton truck. Especially one that may have a lift and bigger tires. Save all that money up you would spend to rebuild it (not smart at all to swap a 700R in without going thru it regardless of what a po says about it) and the adaptors to make the 205 bolt up to it, buy the gear vendors and be done. Even when they are built up they don’t last behind bigger tires with stock gears or big horsepower. I’ve been bitten by more than one of them and am completely not a fan. Also 600 is steep for one down here in the continental states, AK might be different but even a built to hilt unit used down here run 3-500 at best. Not much demand for them anymore with all the never transmission options. And before anyone says it, my TV cables were set right and the three I’ve had fail had all the updates and were the later styler heavier duty K cases. If you aren’t going to use your truck very hard, you might survive. If your going to use your truck as a truck, I wouldn’t do it. The gear vendors units are damn near bomb proof.

Ok 700R rant over carry on everyone else

[kwmech]

There is no 'tail' if you have a 4wd Turbo 350. All the 4wd t350s are the same. The easy way to mate up the 700 is to get an adapter/spacer from Advance Adapters and bolt that in. It will move the t-case back, so some drilling on the frame will be required as well as shortening the rear shaft and stretching the front shaft. Fabrication of the 4wd shifter mount will need to happen also. The other way is to tear down the 700 and put in a comparable short shaft that mimics the 350 output shaft thus not needing the spacer--this would be my recommendation as I have never seen a 700 that didn't need something fixed inside it after being used for a while.

Edit: Everything 57 said above^^^. I'm not a fan either. I've put 2 700s in my Suburban and finally tossed them out for a 4l80e. Last one ran really well for quite a while until one night I came home and put it into park only to find out it wouldn't engage the parking pawl into the gear. Next morning I pulled the pan and noticed a 'washer' between the pawl and the gear preventing lock up. Yeah the washer looks likes one of the thrust washers that retains the needle bearings on the rear planetary gear set. Pulled the washer out so I had park for a couple of months while I got the parts together for the conversion. Still shifted great and drove nice. Now it is sitting on the side of my garage needing a tear down. It is an excellent core for somebody needing aggravation in their life

[Accelo]

The early 700's got a well deserved bad rap. By early I mean 1982-1986.
IMHO The 87-to 93 are a fine transmission. GM made so many changes in 1987 the manual that outlines the changes is larger than the rebuild manual.
If it has the original 1984 transmission in it I would pass.
You can learn how to decode the stamping on the net if interested.
However, I don't know your area. They are all over where I live.
A THM 350 is getting difficult to find. They were phased out of use and superseded by GM's 700R4 starting in 1982. So they are at lest 40 year old technology.
The parasitic loses are less in the 700. All have lock up converters and all have a lower first gear than the THM 350's. That is why I like them.
(not smart at all to swap a 700R in without going thru it regardless of what a pro says about it)
I agree, going through it is best practice and all pro's would say the same thing. Sometimes the Money is difficult to come by ($1700 or so for a rebuild) and you have to take chances.
Up to the buyer. As long as they go into it with open eyes. Kind of like knowing the odds before you enter a Casino?

[jimijam00]

I'd run a 700 before I'd ran a 350. The 350 was no powerhouse. There is a reason all the vehicles with more power came with the 400.

Anyone that does not understand how to adjust a TV cable has no business installing a transmission.

[kwmech]

Originally Posted by Accelo

The early 700's got a well deserved bad rap. By early I mean 1982-1986.
IMHO The 87-to 93 are a fine transmission. GM made so many changes in 1987 the manual that outlines the changes is larger than the rebuild manual.
If it has the original 1984 transmission in it I would pass.

All of my issues have been in 1990 and 1991. Replacements have been GM replacements with a FACTORY warranty. I've even rebuilt a couple of my own for other vehicles with all kinds of updates with drive shells, extra clutches, 5 pinion planetaries, corvette servos valve body updates etc. THEY DON'T LAST long term in trucks --furthest I made it in my Suburban was about 60k miles when things started getting weird and of course at that point it is out of warranty. Sorry I'm used to autos lasting upwards of 200k and I take care of my stuff with servicing. I converted a full size van I owned years ago from a 350 to a 700 and it was one of the best things I did. So I got 1 "good one" so-to-speak out of 6. That trans came out of a wrecking yard with 50k on it. I serviced it and bolted it in. Ran awesome until I sold it, and it had a 400 small block in it.

Why GM put passenger car running gear in a Suburban I'll never know, worst decision ever.

[57taskforce]

Originally Posted by kwmech

All of my issues have been in 1990 and 1991. Replacements have been GM replacements with a FACTORY warranty. I've even rebuilt a couple of my own for other vehicles with all kinds of updates with drive shells, extra clutches, 5 pinion planetaries, corvette servos valve body updates etc. THEY DON'T LAST long term in trucks --furthest I made it in my Suburban was about 60k miles when things started getting weird and of course at that point it is out of warranty. Sorry I'm used to autos lasting upwards of 200k and I take care of my stuff with servicing. I converted a full size van I owned years ago from a 350 to a 700 and it was one of the best things I did. So I got 1 "good one" so-to-speak out of 6. That trans came out of a wrecking yard with 50k on it. I serviced it and bolted it in. Ran awesome until I sold it, and it had a 400 small block in it.

Why GM put passenger car running gear in a Suburban I'll never know, worst decision ever.

Exactly!!!!

[Accelo]

If I was dead set on something that held up to more torque I would step up to the 4L80 or the 6L80. My preference is something with OD.

[Bigdav160]

I have a 4L60 in my '72 K20 ton Suburban. I like it.

But having been a transmission guy for a couple decades I've had my hands in many hundreds of 700r4, 4L60 and 4L60e's.

I'll agree that there are inherent weaknesses in the design but they all don't break at 60k either. I sold a Suburban with 250k and the only transmission repair was a 1-2 accumulator seal. My spouse's S10 Blazer went 225k before the seals got so hard it would take a while in the morning to go into gear. The key to longevity is no abuse and low torque applications.

I built a 700r4 to go behind my big block '67 C-10. It performed well but when I pulled it out to refresh (maybe 10k miles) the steel part of the clutches were beat to death.

If you search you'll find all the details what it takes to make it fit. It's not a straight bolt in.

[MARKDTN]

I'm going to also go on the 700R4 is good side. I have an '83 K20. The original weak 700R4 went 75K miles towing trailers and the pump died. GM dealer put a pump in it and it went another 10K or so before it died again. This time they put a later reman in it and it lasted 75K miles and a pinion seal died in the rearend which eventually took out a pinion gear tooth. This was mis-diagnosed as a bad transmission and it was built again so I can't say it would have lasted forever but it was doing fine. I know people have bad luck with these, but I really have not.

But, if this is an original '84 transmission, I would not do that one. You really need '87 and newer to get the upgrades. But it might be a GM reman with a newer core so worth checking out.