TH350 to 700r4 swap

[R8rPhan]

Starting to sound like I won't need to change much except move the cross member, add a tranny cooler, and buy a tail housing and output shaft..

Is this correct? If so, I'm a happy camper...

 

[HotRodPC]

To be clear, you're saying I already have the brackets/cable I need, but just have to make sure it is adjusted properly once the new tranny is in?

I am 90% certain the same exact Th350 brackets work and I'm 100% positive on the carb you're running is the right geometry that is the same as Th350. I'm pretty certain on the brackets too, but the conversions I did for people, I let them install it and I never heard of anyone coming back saying there was a problem. You'll know if it doesn't adjust right. You'll be able to tell pretty quick cuz the trans will likely shift very very early or very late and you won't have enough adjustment in the cable to make it right if the brackets were wrong.

Curious.. Will my existing 3 speed column and linkage work with a 700r4? I don't care about the shift indicator on the column.. I've already yanked that out anyways...

Or is the total shift linkage travel amount different for the 2 transmissions and the linkage/column will need to be changed to allow that?

Yes, it'll work. Worse case scenario, you might not be able to select Manual 1st gear, but I'm pretty sure you can. I don't recall any detent bracket in the steering column that would keep it from working. If so, just a matter of swapping one from a 700r4 column and changing the indicator in the dash. That's all easy stuff.

 

[HotRodPC]

Starting to sound like I won't need to change much except move the cross member, add a tranny cooler, and buy a tail housing and output shaft..

Is this correct? If so, I'm a happy camper...

I see so many threads and help so many, I forgot that your donor trans is a 4x4 transmission. So yes, you'd need the output shaft changed and add the tailshaft housing then you're good to go. To swap the output shaft though the whole transmission has to be taken apart, the output shaft pulled out and the new one put in. That's all the way to the back of the tranmission so when I say all the way apart, I mean all the way apart with exception of the low/reverse piston which requires a special tool. You won't need to take it out unless you want to replace the seals behind it. Otherwise it's just take it apart, no need to break down any drums or anything, but the front pump will have to come off, the valve body has to come off to pull servos that will hold the bands etc, so it's a bit of a job.

If you don't want to go through all that, see about finding a more common to find working 2wd unit that just slap it in the truck and roll. Just an FYI, the 87 and up units are better and had more bug fixes. 88 had another change that I don't recall now, but 87's up are the way to go. From 88-93 you pretty much have all the good bug fixes.

 

[R8rPhan]

To swap the output shaft though the whole transmission has to be taken apart, the output shaft pulled out and the new one put in. That's all the way to the back of the tranmission so when I say all the way apart, I mean all the way apart with exception of the low/reverse piston which requires a special tool. You won't need to take it out unless you want to replace the seals behind it. Otherwise it's just take it apart, no need to break down any drums or anything, but the front pump will have to come off, the valve body has to come off to pull servos that will hold the bands etc, so it's a bit of a job.

So, it sounds like I might want to look into what it costs to have it rebuilt with all heavy duty clutches, pump and what not if I can get a good price... Just having it out of the truck already would save me several hundred dollars at least...

I know a kid that went to school for auto trans rebuilding, and is a certified tech, but is not working in the industry (Jobs of any kind are few and far between around here for the last 6-10 years)...

So 'maybe' I'll have him come over and help replace the shaft, or even buy a rebuild kit and have him do it here while I watch so I can learn a thing or two...

 

[HotRodPC]

To upgrade the pump and input shaft, buy the output shaft and tailshaft housing, you're probably going to be better off to find a more fitted core, like a 87 or 88 and up 2wd unit. You'd probably spend a fortune getting those other parts when the 87 and up need less updates and are better cores to start with.


As always, you're to far away or I'd have a 2wd early 93 core I'd probably cut loose of for $75 or even another early 93 2wd core that has a break in the bell housing that you could use for your hard part updates for $50.

 

[R8rPhan]

To upgrade the pump and input shaft, buy the output shaft and tailshaft housing, you're probably going to be better off to find a more fitted core, like a 87 or 88 and up 2wd unit. You'd probably spend a fortune getting those other parts when the 87 and up need less updates and are better cores to start with.


As always, you're to far away or I'd have a 2wd early 93 core I'd probably cut loose of for $75 or even another early 93 2wd core that has a break in the bell housing that you could use for your hard part updates for $50.

Why do I need to update the input shaft? It's an 89 tranny.. I thought they had the updated ones?

I'm seeing rebuilt tail housings and shafts going for $65-110 on eBay (for both)... Rebuilt tail housings by themselves for as little as $35

Maybe it would be worth the shipping on one of yours?

 

[HotRodPC]

They do, I thought the first post you said you had donor 4x4 trans from an 84. If it's an 89 then you'll just need the output shaft and tailshaft housing.

 

[R8rPhan]

They do, I thought the first post you said you had donor 4x4 trans from an 84. If it's an 89 then you'll just need the output shaft and tailshaft housing.

Whew!

 

[74 Shortbed]

WOW, my head is spinning

 

[HotRodPC]

The last time I seen someone's head spinning, they needed an Exorcism. You might want to talk to someone.

 

[74 Shortbed]

The last time I seen someone's head spinning, they needed an Exorcism. You might want to talk to someone.

 

[R8rPhan]

WOW, my head is spinning

Stand up slower?

 

[74 Shortbed]

Stand up slower?

That's funny.

 

[Noco77gmc4x4]

Th350 swap to 700r4

I have a 1977 gmc sierra classic 4x4 with a sbc 400 and a th350 automatic tranny. I recently lost my forward gears in my th350. Still has reverse but when I put it on drive it won't go faster than 2mph. I replaced my shift cylanoid, filter and new tranny fluid. All vacuum lines are hooked up, cooling lines, etc. I shifted trough the gears to pump fluid into each gear and checked my fluid level and everything checks out fine but still having issues. Now my question is would i be able to direct swap the th350 out with a the 700r4 that came out of an 85 k5 blazer or would it be easier to fix the th350?

 

[HotRodPC]

I have a 1977 gmc sierra classic 4x4 with a sbc 400 and a th350 automatic tranny. I recently lost my forward gears in my th350. Still has reverse but when I put it on drive it won't go faster than 2mph. I replaced my shift cylanoid, filter and new tranny fluid. All vacuum lines are hooked up, cooling lines, etc. I shifted trough the gears to pump fluid into each gear and checked my fluid level and everything checks out fine but still having issues. Now my question is would i be able to direct swap the th350 out with a the 700r4 that came out of an 85 k5 blazer or would it be easier to fix the th350?

What transfer case do you have? I'm thinking an NP203. If you want the 700r4, it might be a good time to swap to a 700r4/NP208 Combo. Try to find the Transmission, Transfer Case, Crossmember and driveshafts out of a later model truck then it will be fairly easy.

Th350 is done. Forward clutches are worn out.