TH400 to 700r4 swap questions

[dtaylor7897]

Hi. I'm new here so lemme know if something's out of order.

I have a 79 K20 Suburban with a 350, TH400, NP203 (with part time kit), Dana 44, 14 bolt, and 4.10s. I recently purchased a rebuilt 700r4 that is already mated with a NP241. It came with driveshafts from a 85 K10 shortbox.

So my question is, what am I going to have to do to make this swap work. Will I need to swap the driveshafts, or have new ones made? Am I gunna have to do something with the vacuum lines? I just wanna get as much advice before i start tearing things apart and am left without my daily. If there's anything at all I need to know to do this swap correctly please let me know. Thanks. Call me Drew.

[plik]

I believe the fit to the body is different. You might have to cut into the frame and weld on different mounts.

[1967KaiserM715]

Must have got distracted, had this whole reply saved.

New driveshafts, need longer front and shorter rear if I remember right- the ones you got with the transmission won't work for 2 reasons- one is u-joint size, the other is length.

Shift linkage may be different but it is all bolt on-drilling holes, same with transmission crossmember-needs to move back about 2".

Chances are its a np208 as well, a 241 was typically a driver drop, but they made a few passenger drop.

Cap the vacuum lines-is your truck AC? Also you need the TV cable and correct bracket for your engine, wrong cable or bracket will fry the 700 in a few miles.

This is a fairly common swap, and there are a few things to watch out for-planning ahead and comparing what you have to parts diagrams can help a lot.


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[XrayTedd]

Running the 241c tcase you might end up losing a speedometer if it is a vss tail cone. A passenger drop 241c with mechanical speedo was only made in 89. Even at that they were optional depending on whether or not the vehicle came with ABS. I know they make adapters to go frome mechanical speedo to vss. But not sure about the other way around.
You'll want the "W" shaped cross member for the 241c and the 208 tcases.

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[dtaylor7897]

Must have got distracted, had this whole reply saved.

New driveshafts, need longer front and shorter rear if I remember right- the ones you got with the transmission won't work for 2 reasons- one is u-joint size, the other is length.

Shift linkage may be different but it is all bolt on-drilling holes, same with transmission crossmember-needs to move back about 2".

Chances are its a np208 as well, a 241 was typically a driver drop, but they made a few passenger drop.

Cap the vacuum lines-is your truck AC? Also you need the TV cable and correct bracket for your engine, wrong cable or bracket will fry the 700 in a few miles.

This is a fairly common swap, and there are a few things to watch out for-planning ahead and comparing what you have to parts diagrams can help a lot.


Sent from my iPhone using Tapatalk

Where should i go for a TV cable and bracket and where do i hook that up? Also what does driver drop and passenger drop mean? And yea my truck has AC.


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[XrayTedd]

Must have got distracted, had this whole reply saved.

New driveshafts, need longer front and shorter rear if I remember right- the ones you got with the transmission won't work for 2 reasons- one is u-joint size, the other is length.

Shift linkage may be different but it is all bolt on-drilling holes, same with transmission crossmember-needs to move back about 2".

Chances are its a np208 as well, a 241 was typically a driver drop, but they made a few passenger drop.

Cap the vacuum lines-is your truck AC? Also you need the TV cable and correct bracket for your engine, wrong cable or bracket will fry the 700 in a few miles.

This is a fairly common swap, and there are a few things to watch out for-planning ahead and comparing what you have to parts diagrams can help a lot.


Sent from my iPhone using Tapatalk

Where should i go for a TV cable and bracket and where do i hook that up? Also what does driver drop and passenger drop mean? And yea my truck has AC.


Sent from my iPhone using Tapatalk

Driver and passenger drop is which side the front drive shaft comes from the tcase.
As far as the bracket you need the one correct for your carb/throttle body. The TV cable must be the correct length to give you the adjustments needed to set the cable correctly. They're not too difficult to set. They just have to be set correctly.
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[dtaylor7897]

Must have got distracted, had this whole reply saved.

New driveshafts, need longer front and shorter rear if I remember right- the ones you got with the transmission won't work for 2 reasons- one is u-joint size, the other is length.

Shift linkage may be different but it is all bolt on-drilling holes, same with transmission crossmember-needs to move back about 2".

Chances are its a np208 as well, a 241 was typically a driver drop, but they made a few passenger drop.

Cap the vacuum lines-is your truck AC? Also you need the TV cable and correct bracket for your engine, wrong cable or bracket will fry the 700 in a few miles.

This is a fairly common swap, and there are a few things to watch out for-planning ahead and comparing what you have to parts diagrams can help a lot.


Sent from my iPhone using Tapatalk

Where should i go for a TV cable and bracket and where do i hook that up? Also what does driver drop and passenger drop mean? And yea my truck has AC.


Sent from my iPhone using Tapatalk

Driver and passenger drop is which side the front drive shaft comes from the tcase.
As far as the bracket you need the one correct for your carb/throttle body. The TV cable must be the correct length to give you the adjustments needed to set the cable correctly. They're not too difficult to set. They just have to be set correctly.
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where can i get one of those? junkyard?  ? jc whitney? trans shop?


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[XrayTedd]

Any of those places. If you're running the qjet carb. I'd recommend the junk yard. You can probably pull the bracket and cable off one vehicle. Just make sure it's coming off a 350 engine.

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[Captkaos]

A TV bracket is not specific to the engine displacement.  Aftermarket companies make universal TV brackets that work fine too.

[hatzie]

Drew
The V8 displacement shouldn't matter.  You should be able to use the Rochester Quadrajet TH700R4 TV Cable Bracket from any mid-1980's Chevy CK series with a V8 305, 350, or even a 454.  Make sure it's for a TH700R4 Throttle Valve cable and not a TH350C Kickdown cable.  If you can find an original GM part I'd grab that over one from TCI etc.
I wouldn't get a used TV cable.  Splurge and get a new one.

You will probably run into trouble with the throttle arm on your 1979 Rochester Quadrajet.  It will probably not have provision for the correct TV cable hookup point.  There are various commercially available adapters but I cringe when I see some of these cheezy "professionally engineered" solutions.  The guaranteed-to-work, most long-term reliable, and easiest to install solution... is to replace your 1979 carburetor with Quadrajet from a mid 1980's K20 that was equipped with HD emissions and a TH700R4... If it has Metripack electrical connectors on top for the feedback controls it's not the carb you want.  You can still get quality rebuilt Rochester Quadrajet Carbs for around $250.

If your prop shaft(s) are the right length but the Universal Joint caps are the wrong diameter for one or more of your existing axle or new transfer case yokes... you can purchase hybrid universal joints from good names like Precision and Spicer to mate them with the offending axle and/or front transfer case yokes.
I would take this opportunity to replace the 14bolt Yoke straps with original GM parts or upgrade to a U-Bolt Yoke on the axle...  The parts store "equivalents" don't fit as well as the poor GM parts so don't go there.
A short quote from the Pirate 4x4 14bolt yoke article.  NOTE The following is not family friendly because of some well placed curse words...  http://www.pirate4x4.com/tech/billavista/PR-1410_Yoke/
"No parts store I have ever tried, from NAPA to Car Quest ever has them.  That leaves only the GM dealership, where the strap (GM p/n: 3920486) will set you back $3 EACH! and the bolts (GM p/n: 458300 or 14018700) another $2 EACH."

You probably have an NP208C.  There's a round aluminum tag on the rear face of the case with the transfer case model stamped into it. 

You will need to match the speedometer drive and driven gears to your axle ratio and tire size.  Your setup may require a ratio adapter box as well.  If the NP203 has a speedometer ratio adapter box keep it... some of them are getting difficult to find and you may need it to put back on your truck or trade to someone else. If you can provide the axle ratio and the tire size I can probably dig the speedometer gear info out of the parts book speedo gear tables.  If you feel confident you can find this information yourself.  I scanned and posted all six of the 1973-1991 GM parts and illustration books.

[dtaylor7897]

I think I'm going to try to make a bracket and cable from some metal and some throttle or parking brake cables I have around the shop. I don't have time to order one (and no stores have one in stock) as I have to get back to college Saturday and my father said he has fabbed a bracket for the 700r4 on his LeMans. I measured the U-joint caps and they seem to be the same diameter. I took some pictures of the things you mentioned as I'm not sure what exactly I have.

It was 10 pictures so I threw them on iCloud. Lemme know if you have any trouble viewing them. https://www.icloud.com/sharedalbum/#B0SGqkRUiG7FW5N