thm 350 to thm 400 driveline

[toolboxchev]

So I am thinking to replace the 350 for a 400. Would there be a difference in a stock C20 drive line?

Looking to keep costs to a minimum and spend it on the trans!

[James the III]

The th350 is smaller than the th400..
1)cross member moves iirc
2)th400 uses a different yoke on drive shaft
3) drive shaft (one piece) needs to be cut..
4)modulator valve hook up is different so you'll have to account for that..(easy to move)
5) depending what speedo gear sets are in the th400 you might have to change them to get your speedo to read correctly..
6)th400 eats power (it takes more power to turn the guts than the th350) So unless you are making more power than a th350 can take normally, or towing/loaded a lot..
You won't gain anything swapping to the th400.. other than more drivetrain losses from crank to wheels.. If engine is bbc or a turbo'd/blown small block then head straight for the th400. but for a mild 350-383 in a truck that won't be loaded up many times.. you'll gain nada .. other than a lighter wallet

[GASoline71]

Funny how the factory put TH400's behind SBC's in C20's and C30's.

As I've learned over the last 30 years... the loss (maybe 30hp) won't even be noticed.

Gary

[Dead Parrot]

If your TH350 is still in good shape, keep it unless your future plans include a high HP/torque motor.

Had a 68 Impala with a 327/TH400 combo. It would get 16-18mpg at highway speeds with the AC running.

IIRC, there is also an electrical down shift switch that mounts with the carb linkages.

If you can find a donor vehicle that has or had a TH400, most of the swap parts could be obtained from that.

[crazy longhorn]

Originally Posted by GASoline71

Funny how the factory put TH400's behind SBC's in C20's and C30's.

As I've learned over the last 30 years... the loss (maybe 30hp) won't even be noticed.

Gary

The 400 is tuff, but does take a little power to turn....I doubt that it is even 30 ponies, nor would you feel it on the street? On the strip, the Power glide, will take the least amount of hp to turn...(big motor/low gears)= fun maybe one of the other guys can pull the link....but IIRC, the 400 takes about 45hp to turn, the 350 was around 30, with the "glide ' coming in around 18-20 hp to run? I may be off on the numbers, as an old mans memory gets clouded Check it out, see what you find...Longhorn

[James the III]

Originally Posted by GASoline71

Funny how the factory put TH400's behind SBC's in C20's and C30's.

As I've learned over the last 30 years... the loss (maybe 30hp) won't even be noticed.

Gary

Funny how most truck owners back when these trucks and square bodies where new they used them as trucks and towed and loaded it up with the bed.. and a majority powered with a 350/th350 combo
and now most use these trucks and a fun vehicle that even if it is used as a truck, it's a light load from the home improvement store.. not loaded with 1000+ lb in the bed and towing a landscape trailer..

sure if the o/p is going to use the truck as a truck and load it up all the time or tow a bunch of times.. the th400 would be worth it.. towing 1-2 times a year isn't using it as a truck like it would be as new..
I'd rather not have to spend the extra bucks to change over to a th400 if it's not required..
I'd also rather have the hp going to the tires than the drivetrain loss.. 15-20hp difference.. is a bunch in a 200 hp 350. ( most 300-330 hp claimed by owners by the time it gets to the tires, most times less as that claimed hp is well. )
I'd also rather the better mpg not having to turn the extra mass will allow..

But if you are going to tow a race car and trailer a lot, as in all season every week end then sure put a th400 in it if you feel it is "needed"

[toolboxchev]

Thanks fellow enthusiasts. This gives me the needed initial insight for looking at the 400. If I had another 350 core laying around that would be first.

This one may become on the list of possibilities.