2wd th350 in place of 4wd 700r4

[PrairieDrifter]

I have a decent TH350 from a 2wd, and id like to swap it in place of my 700r4. I don't see much life in the future for the 700r4, its just too sensitive of a transmission for me.

My question is what ill need for the 2wd 350 to bolt up to the np208,My understanding is that the 700's output shaft is about two inches longer than the 350's. So that said, I would have to either get a longer output shaft for the 350, or I would have to bring the transfer case closer to the transmission with a different spacer and move the crossmember? Also needing an extended driveshaft.

Also is there a difference in the output shaft of a 2wd th350 vs. a 4wd th350? Would the 2wd 350 possibly have a longer output shaft?

ORD has some transfer case to transmission adapters being offered now but I didn't see one for this swap. I'd like to avoid having to rebuild the transmission which would take the extended output shaft option away, if possible.

If anything I wouldn't mind finding a np205 to rebuild and swap in along with the TH350, they have a 350 to np 205 case adapter, which im assuming would move the transfer case closer to the transmission which would mess with my driveshaft but that's not a huge problem for me.

As of right now im thinking its not possible to mate an np208 to a 2wd 350, I know the bolt patter for the tailcone is the same its just the output shaft and the total driveline lengths are tripping me up and confusing me

 

[PrairieDrifter]

I learned a couple more things. The 700's overall length is a couple inches longer, which is why you need a spacer and the adapter for it to bolt up without moving the crossmember or modifying the driveshafts. So ive got that figured out, now the only thing is the output shaft. From what I understand the 4wd transmission output shafts are shorter than any of the two wheel drive options, that being said I could basically use any 2wd 350 and all I would have to do is cut down the output shaft. But it cant be cut to the same length as a 4wd 350 because the transfer case adapter is setup for that extra 2 inches of length from the 700. But both the 700 and its shaft are 2 inches longer that means the 350 shaft would end up 2 inches shorter maybe 4? This is where I get confused lol

 

[bucket]

You would need a "short tail" 2wd th350 and a fitsall spacer to go between the trans and adapter. HRPC has a thread about the swap... It might even be a sticky.

 

[Swims350]

you can buy the kit and use any th350 you want if you tear the whole trans down and swap shafts. They also include the spacer,

OR

you can cut around an inch or so off the 6 inch short tail th350 use the spacer and bolt the rest up and be done. 1 to 1-1/2 or so last I checked th eone I had. If you get the spacer, throw it on and measure the shaft sticking out, then measure inside the t-case and see what it needs to be. I'm sure mine needed like an inch to maybe inch and half cut off and would work. That shaft can be cut off with the trans all together very carefully. Most would not recomend it, and if you're going to tear it down and swap shafts might as well get the kit.

 

[Swims350]

the adapter for the 700r4 to np208 is the exact same as a th350 it will bolt right on, been there done that. I had a 700r4 in my 99 k1500 with a 241 case, used the same adapter and it's the same as a 208 was going to do my 83 the same way but traded it off before I got around to it, even picked up a checy th350 short shaft to do so.

 

[PrairieDrifter]

the adapter for the 700r4 to np208 is the exact same as a th350 it will bolt right on, been there done that. I had a 700r4 in my 99 k1500 with a 241 case, used the same adapter and it's the same as a 208 was going to do my 83 the same way but traded it off before I got around to it, even picked up a checy th350 short shaft to do so.

Wouldn’t the crossmember have to be moved because the 350 is shorter than the 700? Or did you get the spacer?

 

[PrairieDrifter]

Alright so my th350 has a 6 inch tail cone so it looks like I’m good to go!

Also I found a used 208 about 50 miles from me out of an 87 suburban I think he said, he said it worked fine and the fluid was red when pulled. I offered him 100 bucks.

You guys think that’s a good deal? I’m gonna ask if he has the adapter and the brace for it still, maybe he’ll throw it in for free or like 20 more bucks or something who knows. But I’m looking at a spare one because mine is cracked at the support brace mount.

My plan is to run it until the trans or transfer case goes, and in the mean time get my transmission and other transfer case freshened up and mated together so it can go straight in when the current setup fails.

 

[Swims350]

on a 4wd the trans mount is where the transfer case adapter is. Using the spacer puts that adapter right where it has to be in order to reuse everything.

2wds however the difference is like 3 inches since they mount on the trans body.

 

[bucket]

100 bucks seems good. I know I wouldn't part with mine for that little.

 

[Swims350]

let me break some of this down more for you as well, the swap kit from tekpak fitzal or whatever worked with any th350 as it has the right shaft to mate up and go in place of a 700r4 which uses the same adapter to the t-case and usually is a 208 behind a 700r4.

To use a 6 inch short shaft 2wd th350 that shaft can be cut down as I mentioned above and work with a stock 700r4 adapter to a 208 transfer case.

for a 4wd th350 they had like 3 different length shafts for tt- case setups.

very short 203 shaft that barely sticks out or so from the transmission case.

a lil longer 205 setup that uses the coupling sleeve.

the longest of the th350 4wd's would be a somewhat rare th350-208 setup which was an option in the 80's That shaft is still shorter then a th350 that will go in place of a 700r4 and works with of course a 208, doing this would require the crossmember to move forward some. My guess is 1-1/2 to 2 inches whatever the thickness of the spacer for the swap is. by the swap I mean the spacer for the 350 in place of a 700r4. that is also how much shorter the stock 4wd th350 shaft to 208 setup is then the one needed for the 350 in place of a 700.

I have found those spacers by itself on ebay and then they come in the swap kit, which is almost 200, comes with the spacer, studs, nuts, flywheel dust cover, dipstick and maybe other pieces? I forget now.


If you cannot hunt down an adapter for the 208 try ebay for one or even a 241 case, the 88 I had was a 700 and 241, and I put in a th350 to the 241 and it was the exact same as my 208 from what I could see. The 241 is a driver's side drop t-case with electric speedo, and the 208 of course the opposite.

 

[PrairieDrifter]

on a 4wd the trans mount is where the transfer case adapter is. Using the spacer puts that adapter right where it has to be in order to reuse everything.

2wds however the difference is like 3 inches since they mount on the trans body.

Yes I understand that, the 350 is shorter than the 700 so it needs the spacer between the original adapter. I was mainly concerned with the shaft issue.

You guys have got me sorted out pretty much. I was just having issues understanding the shaft lengths and what not. But now I know I’ve got the right 2wd drive trans to just be able to cut some of the shaft off instead of swapping out the shaft.

Thank you guys

 

[PrairieDrifter]

let me break some of this down more for you as well, the swap kit from tekpak fitzal or whatever worked with any th350 as it has the right shaft to mate up and go in place of a 700r4 which uses the same adapter to the t-case and usually is a 208 behind a 700r4.

To use a 6 inch short shaft 2wd th350 that shaft can be cut down as I mentioned above and work with a stock 700r4 adapter to a 208 transfer case.

for a 4wd th350 they had like 3 different length shafts for tt- case setups.

very short 203 shaft that barely sticks out or so from the transmission case.

a lil longer 205 setup that uses the coupling sleeve.

the longest of the th350 4wd's would be a somewhat rare th350-208 setup which was an option in the 80's That shaft is still shorter then a th350 that will go in place of a 700r4 and works with of course a 208, doing this would require the crossmember to move forward some. My guess is 1-1/2 to 2 inches whatever the thickness of the spacer for the swap is. by the swap I mean the spacer for the 350 in place of a 700r4. that is also how much shorter the stock 4wd th350 shaft to 208 setup is then the one needed for the 350 in place of a 700.

I have found those spacers by itself on ebay and then they come in the swap kit, which is almost 200, comes with the spacer, studs, nuts, flywheel dust cover, dipstick and maybe other pieces? I forget now.


If you cannot hunt down an adapter for the 208 try ebay for one or even a 241 case, the 88 I had was a 700 and 241, and I put in a th350 to the 241 and it was the exact same as my 208 from what I could see. The 241 is a driver's side drop t-case with electric speedo, and the 208 of course the opposite.

Thank you for this info as well!

 

[PrairieDrifter]

100 bucks seems good. I know I wouldn't part with mine for that little.

He says he’s got the trans adapter and the support rod. I won’t say anything about it and see if he’s throwing those in with it. I’ll pull the trigger on it

 

[Swims350]

good deal. I just wanted to give some info that I learned about them just in the last year or so having mine with a 208 and wanting to do a th350, then having a 88 years back that we did have the swap kit in and was on a 241 case.

IMO th350, alot better trans then a 700r4.

A built 700r4 yea probably good, ad overdrive, if ya need it good, but we just never use OD around here much we just use em for play toys around town.

 

[PrairieDrifter]

I need reliability. I don’t like having to worry about the trans going every time I drive the thing. In the not too horribly distant future I would like to do a gear vendors and call that good.