Th350 to 700R? or Th400? HELP!

[Charles90706]

So in the the 3 months I have owned my 86 GMC shortbed I have done some major work with the most recent being the flip kit in the rear and 6inchs off the front.

Two days ago the transmission completely failed. it started slipping and finally didnt engage the gear at all... I added 3 quarts of fresh fluid and made it home to where it is resting in my back yard.

It is currently equipped with a TH350 (which SUCKS because it doesnt have overdrive)

I WAS A TRANSMISSION WITH OVERDRIVE!!!

I have had corvettes and each can with a 700R that shifted great both before and after being rebuilt.

I know the 700R is a option but I am not sure what kinda of price range for supporting parts (torque converter, flex plate, starter, crossmember, tranny mount, drive shaft, etc) it will need new and which ones I will be able to re-use

Is there another option perhaps a TH400? if so what will i need with that?

Main goal is to make this truck more highway friendly, The most it will be towing is a car dolly in southern california...

Thanks in advance for all your help!~

[83burban]

Putting a rebuilt 350 will be your cheapest option, since you wont have to swap any parts over.

Putting a 400 in would be kind of pointless IMO since you are only towing a car dolly and wouldn't really need the added heft of the 400 unless you were towing on a more regular basis. Plus the 400 has different output shafts that would need to be swapped.

I have a very highly built 700 in my suburban - but that's because it sees cross country drives and will be getting a very healthy big-block in the next year or so. The overdrive is very nice - and when I tow anything - I just keep it in 3rd gear to prevent it from overheating. When towing it acts like a 350 only it has a lower first gear to aid in take-off.

As far as swapping in a 700 - Here's the scoop:
1) Felxplate
2) Cross-member (just need to move it back and re-drill holes I believe)
3) Starter
4) Drive shaft if your 350 is a long tail - if not you can pick one up from the junkyard and put new joints in it, get yours lengthened, or get a custom one
5) Torque Converter - You would want to get a new one regardless since you have to rebuild the tranny and shouldn't reuse the old one - at least you'll be able to pick something that matches your camshaft or a future addition of one.
6) You should get a new trans mount regardless - they're only 30 bucks right?
7) Get the biggest trans cooler that you can fit in the rad support area - it will prolong the life of your trans by a lot.

[Charles90706]

Originally Posted by 83burban

Putting a rebuilt 350 will be your cheapest option, since you wont have to swap any parts over.

Putting a 400 in would be kind of pointless IMO since you are only towing a car dolly and wouldn't really need the added heft of the 400 unless you were towing on a more regular basis. Plus the 400 has different output shafts that would need to be swapped.

I have a very highly built 700 in my suburban - but that's because it sees cross country drives and will be getting a very healthy big-block in the next year or so. The overdrive is very nice - and when I tow anything - I just keep it in 3rd gear to prevent it from overheating. When towing it acts like a 350 only it has a lower first gear to aid in take-off.

As far as swapping in a 700 - Here's the scoop:
1) Felxplate
2) Cross-member (just need to move it back and re-drill holes I believe)
3) Starter
4) Drive shaft if your 350 is a long tail - if not you can pick one up from the junkyard and put new joints in it, get yours lengthened, or get a custom one
5) Torque Converter - You would want to get a new one regardless since you have to rebuild the tranny and shouldn't reuse the old one - at least you'll be able to pick something that matches your camshaft or a future addition of one.
6) You should get a new trans mount regardless - they're only 30 bucks right?
7) Get the biggest trans cooler that you can fit in the rad support area - it will prolong the life of your trans by a lot.

Can I just go pull of everything I need from a 3rd gen camaro? (700r, flexplate, starter) or is there a special one i need for my 350ci motor?

How do i tell if the 350 is a short or long tail?

What trans mount do i get?

I have a VERY large cooler as it is so i think ill just use a compressor and blow it out to clean it

[Tx Firefighter]

I can't imagine why you'd have to mess with the starter or flexplate. We used to do the 700 to TH350 swap a lot in the past and always left the flexplate and starter alone. The 700R4 torque converter bolts right to it.

If your current TH350 has a 9 inch tailshaft, there will be no driveshaft mods needed at all. The length is the same and the yoke interchanges directly into the overdrive. Only a 6 or 12 inch tail TH350 would need driveshaft mods.

[ol yellow 72]

i did this swap in a 77 lwb i had and it was pretty simple went from 350 turbo to 700r4 and all i did was move the crossmember, bolt in the new tranny, with the tourque converter, used my same drive shaft, no need to change flex plate or starter, main key is to get the passing gear cable set exactly perfect, because that shift off it and they will burn up fast if they aint right

but its a pretty simple swap, cost my under $100 considering i used pull-a-part for the tranny

[Charles90706]

thats exactly what i was wondering it the th350 components were the same... so basically the only thing i need is the 700r and the converter? and depending on the output shaft length possibly drive shaft

[Charles90706]

One more question... In a worst case scenario the th350 is a "long" one what can i pull the drive shaft out of that will bolt in? camaro? vantura? I dont want to put the 700 in and only need a drive shaft holding me up from driving to and from school

also are there different tail lengths of 700s? what would be the best years to pull a 700 out of a camaro of other chevy...?

how easy is it to install a "corvette servo"?

[PRattenbury]

You shouldn't have to mess with your starter or your flex plate, as stated earlier. You might get lucky with the driveshaft, also stated earlier. What you will face, that was not mentioned so far, is the provisions needed on your carburetor/throttle body for your TV cable that goes to the 700R4. Additionally, your torque converter will likely be a lockup converter, and you will need some way to control it. This is often done by adding a vacuum switch. If you bring it to a tranny shop the whole deal should cost you about $1500. Thatta way you know it's done right. And if the shop is worth its salt, it will stand behind its work.

[mooseknuckles]

If you want to make it more highway friendly you will need an overdrive tranny. a 700r4 is prob your best option, used or rebuilt is up to you....if your gonna tow, put tranny a cooler on it, and never tow anything in OVERDRIVE!!!

[Charles90706]

Originally Posted by PRattenbury

You shouldn't have to mess with your starter or your flex plate, as stated earlier. You might get lucky with the driveshaft, also stated earlier. What you will face, that was not mentioned so far, is the provisions needed on your carburetor/throttle body for your TV cable that goes to the 700R4. Additionally, your torque converter will likely be a lockup converter, and you will need some way to control it. This is often done by adding a vacuum switch. If you bring it to a tranny shop the whole deal should cost you about $1500. Thatta way you know it's done right. And if the shop is worth its salt, it will stand behind its work.

bringing it to a shop is completely out of the question... I do not have the funds to do that. Times are hard and being out of work since july is tearing me up!

Let me clarify my set up a little bit more...

the truck was originally a v6 fuel injected truck with a standard trans

I bought it with a 4 bolt main 350 with a 4 barrel alum. intake but it has a 2 barrel w/ adapter. there is absolutely NO smog equipment on this thing. It has a place for the trans TV line to hook up to but it was not connected at my time of purchase. When i got the truck it wouldnt shift out of first except when it was nearly floored and manually shifted. I looked it over and figured out that the vacuum line was not installed. I hooked it up and the TV line and prefect shifts.

I want to get it running before i put a 4 barrel on.

[PRattenbury]

if you have a th350 now you have a passing gear cable, not a TV cable. They aren't the same. If you don't adjust the TV cable correctly your transmission will eat itself immediately. If you are not familiar with overdrive automatics, don't bother with it. replace your regular automatic.

[Charles90706]

if all i need is an adjustment then i will take it into a shop for the adjustment... as far as the wrench turning part i am fully willing and capable of doing that

[staggerd86c-10]

3.83 gears + 700r4 = 80mph @ 2200rpms(in my truck at least)
Nuff said
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[DetroitDan]

Hey Tx firefighter (or any other who may have the knowledge), what do you know about this swap for a 4wd? I have a th400 and 4:10 gears, love the truck but hate only 3 gears. Here's the thing, my truck has a somewhat rare 205 transfer case that I'm told is different from regular 205s, but I don't know exactly what is different about it. I have automatic hubs in the front. I want to keep the transfer case, in fact I wouldnt consider changing to a different case, unless perhaps this one blew up which seems unlikely.

If I couldn't change to a 700 and keep this case, then I'll probably keep thinking about a gear vendors OD, although I'll never be able to afford one.

thanks