Author Topic: th350 to np208 and new member introduction  (Read 16567 times)

Offline jamiebarnesjr3

  • Newbie
  • Posts: 37
th350 to np208 and new member introduction
« on: March 02, 2009, 08:03:18 AM »
hey everyone i have 1984 k10 scottsdale with a 350/700r4/np208 setup with 33 inch tires and dual exhaust im 24 years old and have owned this truck since i was 16. now the question i have is its on ot 5yh 700r4 and i want to swap it out with a th350 but im not sure how to ive googled the heck out of and now im even more confused 2 million differant opinions and im lost. what i need to know is a cut and dry way to do this as cheeap as possible. will a 2 wheel drive tranny really bolt right up or will a 4x4 tranny bolt right up, do i have to change shafts or buy adaptors. please help im tired of riding the old ppl bus to work thanks everyone.

Offline jamiebarnesjr3

  • Newbie
  • Posts: 37
Re: th350 to np208 and new member introduction
« Reply #1 on: March 02, 2009, 08:43:27 AM »
also while im here the other day i decided to put my truck in 4x4 moved about 40 feet backed up took it out and now when i drive down the road im getting a clunking sound and cant pin point it. i just need some professional help ive got over 7 grand in this thing in the last 8 years new everything please help

Offline Blazin

  • Blazin new trails!
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 6129
Re: th350 to np208 and new member introduction
« Reply #2 on: March 02, 2009, 09:15:25 AM »
First off welcome from New Hampshaa:
Pop into the Welcome thread and introduce yourself.
As far as the TH 350 swap, you say 5th 700R4. Are they used, or rebuilt / new. A 700R4 is a great trans if they are rebuilt and updated correctly.
(1) there are adaptors available from several different companies to swap a 700R4 for a TH 350. 81, and part of 82 1/2 tons came with a TH 350 and a 208. If, and I say if you can find one of these stock pieces, and a short shaft two wheel drive TH 350 it will be a bolt in swap, with a little bit cut off the output shaft. You will need to modify the rear drive shaft length. Can't remember, but also need to move the cross member too, I think.
« Last Edit: March 08, 2009, 01:22:40 AM by Blazin »
Some people are like Slinkies. Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs

Offline Captkaos

  • OWNER and Administrator
  • Administrator
  • Senior Member
  • *****
  • Posts: 18118
    • http://www.73-87chevytrucks.com
Re: th350 to np208 and new member introduction
« Reply #3 on: March 02, 2009, 05:45:33 PM »
If you are replacing it with 700R4's that are used, you are going to be disappointed everytime, I would say the same would happen on any trans from the Salvage yard unless you saw the truck drive in the same day.

Only other thing I would add is a 2WD trans WON'T work on a 4WD application unless you tear it completely down and replace the outputshaft.  If you are going to do that, rebuild it.

Offline joesgarage71

  • Wrench
  • Senior Member
  • ****
  • Posts: 1157
Re: th350 to np208 and new member introduction
« Reply #4 on: March 02, 2009, 05:48:27 PM »
You should be able to get a used Adapter (GM)  350/208 there out there check your local boneyard.
 Sell all the 700 stuff there is someone wanting that to do that swap(350 to 700. Maybe you can find someone to swap parts with you.
 Steve
78' K-20 355/SM465/twin stick 205 6" on 36's
14 bolt FF/big bearing Dana 44 4.56 gears

92' GMC C-1500 454/4L80E/14 bolt

Offline werewolfx13

  • Junior Member
  • ***
  • Posts: 831
Re: th350 to np208 and new member introduction
« Reply #5 on: March 02, 2009, 08:34:33 PM »
If it were me, I'd build an updated 700r4 for it and not worry about it. A th350 isn't much if any stronger than an 87-92 700r4 (4l60), and you'll lose overdrive and a lower starting gear. Auto transmissions aren't that hard or complicated to work on, sit down with a quality book (VileZambonie can recommend a good one if he pops in here), read through it, and then tear into it. You'll need a clutch press, torque wrench, snap ring pliers, a short chunk of a 2x4, about 6" long is plenty, a rubber mallet, and some basic sockets. A tub of Vaseline, and a few quarts of transmission fluid to soak the new friction plates in overnight are also needed. A small pick set comes in handy as well.
Chris
'83 Chevy c10 Silverado SWB
'76 Chevy k20 LWB 6.5'x8' Flatbed
I know that you believe you understand what you think I said, but I'm not sure you realize that what you heard is not what I meant.

Offline Captkaos

  • OWNER and Administrator
  • Administrator
  • Senior Member
  • *****
  • Posts: 18118
    • http://www.73-87chevytrucks.com
Re: th350 to np208 and new member introduction
« Reply #6 on: March 02, 2009, 08:54:35 PM »
http://atsg.biz/ has the book that I recommend.

Offline Blazin

  • Blazin new trails!
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 6129
Re: th350 to np208 and new member introduction
« Reply #7 on: March 03, 2009, 03:44:11 AM »
Not sure about other areas of the country, but factory GM TH 350 to NP 208 adapters are about as easy to find as hens teeth around here as they were only used for the two model year run.
That being said.
With a factory GM TH 350 to a NP 208 adapter a 2 wheel drive short tail shaft TH 350 WILL work. Only modification needed to the transmission is the output shaft. You have to remove the tail shaft housing, and cut about 3/4" cut off of the output shaft. This can be done without removing the output shaft.
My 81 Blazer has a short tail shaft 2 wheel drive TH 350 in it. I removed it from my 74 Malibu, did the above mentioned tail shaft mod, and installed it in  my Blazer.
« Last Edit: March 08, 2009, 01:24:30 AM by Blazin »
Some people are like Slinkies. Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs

Offline fitz

  • Senior Member
  • ****
  • Posts: 1990
Re: th350 to np208 and new member introduction
« Reply #8 on: March 03, 2009, 09:15:26 PM »
Check with Captkaos and see if he deals with Advanced Adapters products.
I pulled this turbo 350 from a 91 Full size Blazer. It's a 2 W.D. turbo 350 with an adapter kit to replace a 700R4/4L60 mated to a 208/241(I'm not sure who made this kit). It consist of a replacement output shaft(You have to brake down the trans to install it) and an aluminum spacer. This set up uses the stock 700R4/208 adapter and lets you use the original driveshafts. 
If you want a 350/208 set up this may be the way to go. Like Blazin said the 350/208 adapter is a rare item.   

Offline choptop

  • Senior Member
  • ****
  • Posts: 2476
  • Extended cab fanatic
    • conversiontrucks
Re: th350 to np208 and new member introduction
« Reply #9 on: March 03, 2009, 09:40:20 PM »
I never thought about the th350/208 being rare. I have that setup in my 85 excab that the previous owner installed inplace of the 700r4. With the 35's, I dont miss it much.
76 C10 Choptop,76 C10 Swb
85 C10, 85 K10, 85 K20,86 C10,86 K10 (all extended cabs)
86 C30 extended crewcab

Offline Blazin

  • Blazin new trails!
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 6129
Re: th350 to np208 and new member introduction
« Reply #10 on: March 03, 2009, 10:26:37 PM »
GM only used the TH 350 with the 208 for two model years, and only in 1/2 tons.
Some people are like Slinkies. Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs

Offline joesgarage71

  • Wrench
  • Senior Member
  • ****
  • Posts: 1157
Re: th350 to np208 and new member introduction
« Reply #11 on: March 07, 2009, 06:35:36 PM »
 Acording to this the 700 and the 350 share the same bolt pattern, So the adapter you have should bolt to the back of a 350.
http://advanceadapters.com/product/2328/%28P/N-AS-6800%29-1.5%22-TH350/700R-ATLAS-ADAPTER.html
78' K-20 355/SM465/twin stick 205 6" on 36's
14 bolt FF/big bearing Dana 44 4.56 gears

92' GMC C-1500 454/4L80E/14 bolt

Offline 85 1 ton 4x4

  • Newbie
  • Posts: 3
Re: th350 to np208 and new member introduction
« Reply #12 on: March 07, 2009, 07:17:00 PM »
all the tranny shops i haved talk to said a 700r4 is a turbo 350 with overdrive.just build your 700r4 to hold the power better.but if you have to switch go with a turbo 400.it will take any abuse you can throw at it if built right.turbo 400 and 205 transfer case is a good combo.

Offline Blazin

  • Blazin new trails!
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 6129
Re: th350 to np208 and new member introduction
« Reply #13 on: March 08, 2009, 11:39:20 AM »
Bolt pattern is the same, but you need a longer adapter to use the TH 350.
Some people are like Slinkies. Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs