Th350 to 700 swap?

**rebel4wd** · 03-03-2009, 11:41 AM

Hello all, new to the forums. My buddy has an 86 GMC 2500 van with the 350 and a TH350 with 9" tailshaft. The trans. just went out, and we cannot find a used long tail Th350 anywhere. Heres my question- can we swap in a 700R-4 out of a similar van like 84-87 with the driveshaft and vacuum switch for the lockup converter? Any other mods we need to make to speedo/ tv cable? Thanks for any input.

**Jimmiee** · 03-03-2009, 01:25 PM

Originally Posted by rebel4wd

Hello all, new to the forums. My buddy has an 86 GMC 2500 van with the 350 and a TH350 with 9" tailshaft. The trans. just went out, and we cannot find a used long tail Th350 anywhere. Heres my question- can we swap in a 700R-4 out of a similar van like 84-87 with the driveshaft and vacuum switch for the lockup converter? Any other mods we need to make to speedo/ tv cable? Thanks for any input.

You can swap in a 700. You may need a new flex plate unless the one you have is drilled for the 700 converter. You will also need the dipstick, dust shield, and TV cable. The drive shaft may or may not work depending on the length of the yoke. Sometimes the drive shaft will just drop in and other times you will need to have it lengthened. The shifter <prndl> will be missing OD but thats no big deal.

Keep in mind the early 700's have governor controlled lock-up and later 700's do not. If you get a later 700 without the governor controlled lock-up you will need a conversion kit to make the lock up come on in 4th gear. Otherwise without the governor control lock up you will have lock up right on top of 2nd gear. The kits are available on line and some come with the vacuum switch which is desirable. You may also need an adapter on the carb where the cable attaches in order for the TV geometry to be correct. Some Quadra-Jets have the correct geomerty and some do not. Most other carbs need this adapter. Edlebrock and others make a kit.