305 2wd 700R4 swapped to a 350 4x4 with ex fried TH350? - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 01-18-2009, 11:38 PM   #1 (permalink)
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Question 305 2wd 700R4 swapped to a 350 4x4 with ex fried TH350?

So I am posting for a friend.....he has a 1979 K5 with the 350 and TH350 transmission and transfer case. The TH350 is fried, so I know 700R4's are a popular and inexpensive upgrade. One of my other friends has two 305's and 2 700R4's available. The 700R4's are from a 2wd application. $400 all or nothing deal for 2 transmissions and 2 motors with all wiring included.

I believe 305 transmissions have a 21 spline output shaft and 350 transmissions have a 23 spline output, but as far as I know you can swap them . What has to be done to get the 2wd 700R4 to mount up to the transfer case? Since obviously a transfer case will be bolting up to the 700R4 instead of a driveshaft.

Also are there any length difference between a TH350 and 700R4 in terms of driveshaft length and crossmember mounting point?

Thanks in advance!

Last edited by Blaine B.; 01-18-2009 at 11:39 PM.
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Old 01-19-2009, 08:25 PM   #2 (permalink)
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Old 01-19-2009, 08:45 PM   #3 (permalink)
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First off there is no such thing as a 305 transmission. The th350 tranny is gonna have a 27spline output shaft going to the np203 that is in your buddys rig. Why don't you take the $400 and put it towards rebuilding the th350 that is already in the truck? You will be $$ ahead instead of trying to adapt the 2wd 700r4 to a np203, trust me.
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Old 01-19-2009, 08:49 PM   #4 (permalink)
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I did not mean a 305 transmission but rather meant the 700R4 that was paired up with the 305. I will pass your comments along to my friend here, thank you for replying!
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Old 02-05-2009, 12:49 PM   #5 (permalink)
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If it still helps...

The 2wd 700R4 will need the output shaft changed to a 4x4 shaft. ~$50 part, but it goes in through the front of the case. Whole thing comes apart for that.

700R4 is longer. Both driveshafts and crossmember will have to be changed.

TH350 uses a kickdown cable and 700R4 uses a TV cable. The bracket at the carb will have to be changed. Wrong or misadjusted TV cable will barbecue the transmission within minutes.

It's a good swap, but not the low buck alternative.
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Old 02-05-2009, 07:57 PM   #6 (permalink)
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He hasn't bought a transmission yet but thank you, it looks lik the 700R4 isn't the best choice....

Do you know anything about the TH400 swapping in? Is there any difference in the case length between a TH350 and TH400? He really wants that 4th gear if possible.

Thanks again!
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Old 02-06-2009, 11:03 AM   #7 (permalink)
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Quote:
Originally Posted by Blaine B. View Post
He hasn't bought a transmission yet but thank you, it looks lik the 700R4 isn't the best choice....

Do you know anything about the TH400 swapping in? Is there any difference in the case length between a TH350 and TH400? He really wants that 4th gear if possible.
TH400 is bigger, heavier, and longer. And it's a 3-speed. Uses an electric kick down and a vacuum modulator. As far as I know, they don't have a lockup torque converter so gas mileage will drop.

The 700R4 is certainly a good choice. Overdrive, and a lower 1st for better crawl speed and more launch off the line. Since newer K5's came with it, you can source bolt on driveshafts and a crossmember from a junk yard.

Still, likely pricier than just rebuilding the toasted TH350.
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Old 02-06-2009, 11:05 AM   #8 (permalink)
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Interesting, I was thinking the TH400 was a 4-speed. Oops!
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