Which transmission for 1984 GMC pu?

[used red MN]

I believe it came from a '78 1ton puckup. However the adapter I've found online comes with a new tail shaft for the 32 spline adaptation.

I am not sure what you mean by “tail shaft” but the tail shaft in those ATs as in the 350, 400, 700R4 is basically the last part out on tear down/ 1st part in for reassembly. As is the case with most RWD AT’s.

 

[ADoble]

I am not sure what you mean by “tail shaft” but the tail shaft in those ATs as in the 350, 400, 700R4 is basically the last part out on tear down/ 1st part in for reassembly. As is the case with most RWD AT’s.

Correct. It comes with a new one (requiring trans work) to get the 32 spline which is normal w/the th400 to match the np208, which i believe is a 27 spline.

this is the adapter: https://www.advanceadapters.com/th400-x-np208-tcrepl700r-4-long-foot

 

[fusion1]

There might be a simple solution
Retire the old girl

 

[matthies]

There might be a simple solution
Retire the old girl

NEVER, best trucks ever made.

 

[ADoble]

There might be a simple solution
Retire the old girl

Not in the relm of possibility

 

[ss55]

There might be a simple solution
Retire the old girl

I agree. Half ton pickups do not hold up well pushing snow plows, once the frame cracks they are pretty much disposable in that application. The original post is now eighteen years old. Odds are that pickup is long gone by now, unless it was used far south of the Mason-Dixon Line.

 

[scootergmc]

I reread your question.

You want to swap a 2wd TH400 transmission into a 4wd TH350 truck, yes?

Correct. It comes with a new one (requiring trans work) to get the 32 spline which is normal w/the th400 to match the np208, which i believe is a 27 spline.

this is the adapter: https://www.advanceadapters.com/th400-x-np208-tcrepl700r-4-long-foot

By the time you do and buy all the stuff that is required to be done, I think you would've been much further ahead just rebuilding the TH350 and a new torque converter. But if time is not money, then perhaps it is.

 

[ADoble]

I agree. Half ton pickups do not hold up well pushing snow plows, once the frame cracks they are pretty much disposable in that application. The original post is now eighteen years old. Odds are that pickup is long gone by now, unless it was used far south of the Mason-Dixon Line.

 

[ADoble]

It's a rust free GA truck it's whole life. Never touched a plow.

 

[ADoble]

I reread your question.

You want to swap a 2wd TH400 transmission into a 4wd TH350 truck, yes?



By the time you do and buy all the stuff that is required to be done, I think you would've been much further ahead just rebuilding the TH350 and a new torque converter. But if time is not money, then perhaps it is.

Well mostly yes. All the 6.2 diesel 1/2 tons as I understand it started life with 700r4's. Mine now has a th350 which is how I bought it. The th350 looks kinda rough they pulled peanut carts w/it on a farm (probobly why it's on it's second trans). I am the second owner and it is rust free w/80k original miles. The freshly rebuilt trans I have is a gm th400 from a 78 1 ton 2wd truck. I know it will fit w/the adapter kit listed in the post above. I was hoping someone had also done the th400 swap and might have some insight on what other things I will need that im not thinking of.

I am also looking into getting the th350 rebuilt instead, but the th400 is a much more bulletproof trans, and the top pic for me. This is a project truck not just reviving a junker. I'm from Maine so I understand the rust belt, but here in GA people still daily these square body's.

 

[used red MN]

I was hoping someone had also done the th400 swap and might have some insight on what other things I will need that im not thinking of.

What did they do with the vacuum modulator on the 350? Just leaving it unhooked is really not the right answer. There may be a work around in the valve body for your TH400 but you would have to know what it is and make the change. Or find out what they did with early HummVees that use the TH400 with the 6.2. They make these but the extra $200 probably isn’t part of your screaming deal transmission TH400 to TV vacuum modulator adapter
Also the TH400 uses an electric kick down but you got the gear shift for that.
Always fun to hear about those that tread on in oblivion.

 

[ADoble]

I reread your question.

You want to swap a 2wd TH400 transmission into a 4wd TH350 truck, yes?



By the time you do and buy all the stuff that is required to be done, I think you would've been much further ahead just rebuilding the TH350 and a new torque converter. But if time is not money, then perhaps it is.

Well mostly yes. All the 6.2 diesel 1/2 tons as I understand it started life with 700r4's. Mine now has a th350 which is how I bought it. The th350 looks kinda rough they pulled peanut carts w/it on a farm (probobly why it's on it's second trans). I am the second owner and it is rust free w/80k original miles. The freshly rebuilt trans I have is a gm th400 from a 78 1 ton 2wd truck. I know it will fit w/the adapter kit listed in the post above. I was hoping someone had also done the th400 swap and might have some insight on what other things I will need that im not thinking of.

I am also looking into getting the th350 rebuilt instead, but the th400 is a much more bulletproof trans, and the top pic for me. This is a project truck not just reviving a junker. I'm from Maine so I understand the rust belt, but here in GA people still daily these square body's

What did they do with the vacuum modulator on the 350? Just leaving it unhooked is really not the right answer. There may be a work around in the valve body for your TH400 but you would have to know what it is and make the change. Or find out what they did with early HummVees that use the TH400 with the 6.2. They make these but the extra $200 probably isn’t part of your screaming deal transmission TH400 to TV vacuum modulator adapter
Also the TH400 uses an electric kick down but you got the gear shift for that.
Always fun to hear about those that tread on in oblivion.

The modulator on the th350 was left unhooked. Again from what I understand they make a diesel specific one which is hooked to the injection pump to get its vacuum. I have a B&M floor shifter to go with it too. There may also be a manual kick down swap also but I am not positive.

 

[matthies]

Let's hope the new trans is a vac kickdown, as I don't like the electric kickdown on my 84 K10 but gas burner. If electric there is a switch to mount to your accelerator pedal. I know I had to change output shaft on mine but can't remember if it was the spline count or I had a long shaft output. 30 years ago. But thinking a short shaft 400 went right in, as what I have is a 400 trans.

 

[TheBartman47]

If you want to spend some money and have a reliable setup, AND want overdrive, then get a "bulletproof" built TH350 or a TH400 and a GearVendors under/overdrive bolted on replacing the tail housing. The TH700R4 is not a strong transmission, especially when towing, but with a GearVendors under/overdrive you can still tow with that with the overdrive engaged. My 1975 Monte Carlo is setup with a TH350 plus the GV under/overdrive...