TH350 to TH400 swap - whats needed?

[demian5]

Hey Im sure this has been beat to death. I currently have a short shaft 350 in my long bed. I need a trans rebuild and have a short shaft 400 in the garage I could get rebuilt and get the parts together for a swap. I just blew up the motor and plan on a different motor with added HP. 350 is great cause it doesn't take as much power as the 400 to turn, but the 400 would be pretty bulletrpoof.

What do I need for the swap? The truck is currently a column shift and id like to keep it that way. I know Ill need to put the kickdown switch on the pedal assembly.

What else?
New front driveshaft?
Shift linkage? - Can I just move mounting in the frame?
Cross member?
Flex plate? (I wouldn't think so)
Dipstick?

Thanks!

[demian5]

I shoulda done the search. I'm finding articles and posts all over for it now. If you have an additional feedback, Im welcome to it.

Maybe I should just rebuild the 350 so its not such a pig.

[trac209]

Originally Posted by demian5

I shoulda done the search. I'm finding articles and posts all over for it now. If you have an additional feedback, Im welcome to it.

Maybe I should just rebuild the 350 so its not such a pig.

I went from a turbo 350 to a turbo 400 in my nova and I noticed the seat of pants change somewhat. The engine was fairly stock though but in a light car like that I did see a difference. If your engine is really torquey I wouldn’t worry about the power loss as it’s minor.

[weim55]

Maybe I should just rebuild the 350 so its not such a pig.[/QUOTE]

X2 there's really no reason to upgrade to the TH400 unless you're towing heavy stuff constantly or couple hundred horsepower above stock and running it HARD. I've used-built many TH350s for various mild-medium above stock applications with zero failures.

Steve weim55 Colorado

[Coley]

...you'll need more money for gas.
The TH400 uses more energy to run it so that shows up in reduced gas mileage.

All good
Coley

[slocityk20]

So in my understanding, if the truck is 4x4 you will have to move the cross member that is riveted to the truck that the transfer case sits on back. You will have to change the shaft on the transfercase (assuming NP205 27 spline) to be compatible. The TH400 is about 10'' or so longer so you will more than likely have to shorten the rear driveline and lengthen the front drive line.

Now as far as a 2wd application I goes I would just assume you would have to move the transmission crossmember and shorten the rear drive line.

I am by no means an expert but that was the research that I found when i was thinking about doing the same thing.

Thanks!

[kwmech]

Originally Posted by slocityk20

Now as far as a 2wd application I goes I would just assume you would have to move the transmission crossmember and shorten the rear drive line.

Thanks!

That's 'bout it, the cross member will move to next set of holes in the frame. Cooler lines will bolt up, linkage is in the same spot, same dust cover, same flex plate, same rubber mount. Front of the driveshaft upgraded to a 1350 joint.