TH400 to700R4 swapdriveshaft question

[72 K20]

Hi every body !! I have a question !!
I have a 72 C20 with a big block ,,, I am swapping the big block out for a small block. The truck has a TH400 in it now and I am putting in a 700R4.

My question :
If I install the small block frame mounts in the stock location will the original driveshaft from the TH400 work with the 700R4 ?

Thank you in advance for any and all information !!!

Have a great day !
Tom

[LockDoc]

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I don't know about length but the front yoke is different. The TH400 is bigger in diameter than the th350/700r4.

LockDoc

[michael bustamante]

Length will be different and you will probably have to relocate the cross member too

[davischevy]

I had to relocate the crossmember and shorten the driveshaft and the front yoke is different.

[72 K20]

Thank you for the replies !!! I was thinking wrong ,,,, I thought the th400 and the 700 were the same length and same yoke. That's why I asked here ,,, to get straightened out ! Thanks guys ! Now I know what I need to do !

Take care everybody !!!
Tom

[wbc409]

TH700R4 uses the same slip yoke as th350. If you are going to do any towing the th400 is a much stronger transmission. I would recommend upgrading, I believe it's the sun shell. The original 's are stamped steel and prone to cracking.

[wbc409]

Before you sell your th400 it may have some expensive factory installed parts. Namely the clutch hubs. If you know a tyranny guy it may be worth it to open it up to see what's in there. It's out of a big block 3/4 ton it most likely has the heavy duty 5 clutch hubs.

[70's luvr]

I just did this. I used the 700r4 drive shaft (you have to) and had the back half shortened. Napa supplied the conversion u-joint and I move both the trans cross member and the carrier bearing cross member forward.
Save that turbo 400..you just never know.

[Bigdav160]

The torque of a big block is HARD on a 700R4. Even built ones.

[tranz am]

For the 454, only one overdrive will handle that. The 4L80E .

[71K20chevy]

Here's a few tips if you're keeping the 700R4.

The sunshell should absolutely be replaced with at the very least a GM heat treated one. Borg Warner High Energy frictions are said to be some of the best 700R4/4L60E clutches there are. Also check with a straightedge the reverse input drum where the band clamps. If there's any cupping at all, it has to be replaced.

Just my experience with a 4L60E (basically the same as 700R4). Mine has been pulled 3 times and this time I did a ton of research to find out what the problems were. Works fine now!

[70's luvr]

Good advice Andy. I'm doing this as a "proof of concept" with the Dana 60/4:10 gears then pulling the whole truck apart to build it right.

[Turbo1dr]

A 200-4R would be a direct bolt in. Just move the cross member back and change the yolk.
Plus, it has a better gear ratio spread than the 700.

And before anyone says the 200-4R is weak, I have one behind a 600 rear wheel horsepower engine and I've never had problems yet.