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transmission options and opinions

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I've been through this debacle so I know a little bit (assuming you have the JTR crossmember or something similar). I was running a TH350 but I can't stand turning 3200 down the highway. 


700R4 is further back by about an inch if you run the tailshaft housing JTR says not to (early caprice style). It'll be about 3-4" back if you run the JTR recommended tailshaft housing (from the late model caprice). The 700R4 however allows you to keep the same length driveshaft (it's a slightly longer transmission but it won't bottom out). You may find you'll need to also modify your exhaust routing and hammer the tunnel out a bit more because of how large the 700R4 is compared to the TH350. 


Muncie 4-speed of certain years will bolt up in the stock location. I've read they changed the length of the muncie some year and the mount moved slightly. The later model will be in the same location as the TH350. The earlier ones I believe are a little forward as they are like an inch shorter than the later model ones. However, the Muncie is shorter overall than the TH350 in most applications (some say its the same length. The general consensus including me find they're around 2-3" shorter) so you'll need to modify your driveshaft.

A muncie doesn't gain you anything as it's still a 1:1 final drive just like the TH350. I'm running an NP440 out of an '80's Chevy pickup (you can find my thread in this subforum covering my swap) and the transmount bolted right up to the stock TH350 crossmember and in the same TH350 location. I did however have to get a new driveshaft 3" longer than my TH350 one and a small modification to the shifter box placement.


T5 and T56 I'm almost certain are further back but I could be wrong here (these pull big money around me so I never looked into them).


So in the end it's what do you want. Stay auto or go manual? 4-5-6 gears? Either way something will need modifying.

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I recently swapped out my TH350 for a built 200-4R in my late '74 260.  The transmission crossmember was the only major change required, as the mounting points on the 200-4R are a few inches further aft than on the TH350.  I fabricated a new trans mount, but you can purchase pre-made mounts from a variety of sources.  


A 700-R4 might be a pretty tight fit in your '71, especially if you're running a JTR-style mounting position for the engine.  Typically requires widening the trans tunnel...some do it with a BF hammer; others actually fabricate a new tunnel.

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I don't think that's possible to do. I say "think" because I'm sure somewhere on the "interwebs" someone has done it.

But there isn't enough case space nor the correct fluid passages or anything of that nature to support an internal overdrive (why the 700R4 is so much larger). It's easier to just swap in a 700R4 or 200R4 (if space is a concern) and be done with it. Yes you'll have to move your crossmember but that's not the end of the world. It's an easy job. About as easy as replacing the transmission. Few new holes and you're good.


If you have a built TH350 you can always tack on a gear vendors overdrive unit behind it. It'll make the driveshaft super super short (probably around 10"-12" with the factory R200 longnose) but if you have a ton of money invested in the trans it's an option. They aren't cheap though. For the money a gear vendors cost you could sell your built TH350 and buy a built 700R4. But for most just swapping is way easier.

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