OK. I'm swapping a 383 into my 69 which has a T400. The 383 had a T350 with a Hughes 3000 RPM TC attached.

I want to keep the T400 in there, as this swap is temporary. If I go with a T350, I'd need a different driveshaft (T350, out of a 3rd gen, is shorter.) I researched the crap out of swapping the flexplate since both engines are externally balanced, to discover that's a no-go.

But then, I stumbled on to the conventional knowledge that a T350 TC will fit on a T400. If I could swap the TC's that would solve a lot of issues, making this swap essentially a bolt in (I also scored SBC headers for a 69)

So, I attempted to make the TC swap. I'd looked at the pump shafts and on a quick inspection, they appeared to be identical.

Well, as it turned out, that requires the word "almost."

I took pictures as I'm kinda keeping a journal for all of this so my daughter, who will ultimately get the 69, can understand what's happening... and also for any further mechanical issues down the road.

That said, I cannot get the donor (T350) TC to seat on the T400.

I can get it on the shaft. I feel it engage the serrated edge. But I can't get that final "thunk", and the distance between the front pump and the end of the shaft on the TC is about an inch, the surface of the TC itself and the edge of the bell housing is about a half inch inside.

When I look at the output shafts, I notice a substantial "nose" on the end of the T400 shaft,, maybe 3/8's of an inch.

Is that what keeps it from seating?

Anyway, at this point, I'm open for suggestions. Am I overlooking something? The T350 TC is SUPPOSED to fit, Is that incorrect? Can the front of the T350 TC be enlarged a small amount so the shaft can get that last, critical space?

I don't speak transmission or torque converter, so thanks in advance for your help.



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Is the 383 externally balanced because of the stroker crank?
Just wondering,you didn't say what engine you have in there now so wondering why it's externally balanced.
Is it a 400 SBC? All other SBC 1986 and earlier are external,something later?
Sorry I'm no help here,I'd probably just try and pick up another driveline myself.
That or get the correct flexplate,there must be a flexplate for that application available somewhere.
Here's what you need I believe assuming you have the two piece rear main seal.
https://www.skipwhiteperformance.com...4002-fp_94795/

 

Yeah... 383's are externally balanced, so this one is as well.

Because it has vortec heads on it, I'm thinking it was a 350 with a stroker kit. I can double check the casting number.

And, I've been looking those over.... it looks like the direction I'm going to go.

Thanks!

 

Basically a 383 is a 350 with a 400 crank,Chevy never made a 383 from the factory.
If the deck hasn't been resurfaced you can find what year model car or truck it came in on the pad in front of the passenger side head.
https://www.nastyz28.com/chevy-engin...-stampings.php
Here's some good info once you discover what block you have.
https://helpcenter.jegs.com/hc/en-us...ce-Cheat-Sheet

 

it may gave been decked, there's no visible number on that pad.

The number on the back of the block is 14093638. Also has 57 LG SGI.

The flex plate is externally balanced, so I'm thinking in terms of getting an externally balanced flex plate for a 400 that has the dual set of holes for both a T350 TC and for a T400 TC...

Then using the TC that was already in the T400. There wasn't any issue with it... I was only doing the TC swap to fit the flex plate already on the 383.

So now, maybe a dual, externally balanced flex plate is the way to go?

 

I think that's your best bet,doesn't matter much what the block is if it has an externally balanced 400 crank in it anyway.

 

The Th350 is out of a third gen, It would be a lock up converter. Its been a long time since I messed swapping parts around on the older cars but I seem to recall running a lock up converter on a trans that did not support it was bad. If pressure got into that circuit and locked the converter up it would send clutch material all through the trans. Don't take my word for but I would focus on that in my research.

If I remember right, you could go 350 converter in a 400 but if you tried to go the other way you could have a size problem.

 

In this case, it was a 3 speed as opposed to a 4 (OD). I was running a Hughes 3000 stall in it.