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th350 to 400 swap.

wage92

wage92

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I have searched and this is covered a bunch but i just wanna make sure i got this right. I have a good working th350 and 203 tcase. But my engine im building will have about 450hp and 500tq (406sbc) so im thinking the th350 wont be enough or will be borderline. What is required to swap in a th400 if i got a new tranny and tcase? the output splines are different and id have to modify the driveshaft and crossmember. is that all? i heard somewhere that the th400 has electronic kickdown or something?
 
The 205 uses elec kickdown hooked to the gas pedal, it also uses vacuum as well. I dont run the electric kickdown, as I have a slap shifter and I shift it manually anyways, but it is helpful on a column shift. Lokar sells them at around 40$ I believe. The 350 can be built to take that, but I would junk that 203. You can pick up 400/205 or 400/208s pretty cheap, depending on what your looking for. The lower low of the 208 or the brute reliability of the 205. I see them for 200 to 400$ depending on the shape.

Driveshafts might have to be messed with, depending on the t-case really, as the 400 and 350 are very similar in length. The crossmember will change if you change t-cases. Exhaust could get in the way depending on how its ran.
 
so it would be worth it to go with the 400/205 say, because at first i was going to rebuild the 350 and call it a day, but it was going to cost me like 300-400 bucks so i was thinking i could pick a th400 and tcase up for that, throw some seals in it and be good to go...
 
My 400 was untouched from 1980 when I got it, never opened up at all, cept for the pan. Had factory clutches in it, and been through a mud truck. It was fine. I would go through it, as even the 400 has weak points. And perfect time to add a shift kit, maybe put extra clutch/plates in it like I did mine. And blah blah. I am a huge fan of the 205, especially over the 208. I like it mainly for my twin stick, and its ability to take a whooping and keep on truckin, and low low isnt a huge deal in a mudbog, and I make up for it anyways with my 454.

Some 205s come with a slip yolk, like mine unfortunately did. Some are factory fixed yolk. I would prefer the fixed yolk for sure if you can find it.

So overall, I would go for the 400/205. Bullet proof, and your HP/TQ will more than make up for your lack of a low, unless your trying to run 44s on 3.73s or something. lol


And lastly lastly, the 400 requires no special tools to rebuild, except a 12 point 12mm socket IIRC, for something in the valve body. Its easy greasy to rebuild, my dad showed me how to do it without even using feeler gauges and just using an air gun. Now I can do mine in a lil over an hr after it hits the bench, not to bad. You could probably find a You-Tube video or something equivalent to show you step by step on how to do it.
 
todays parts a built th350 will hold just fine.

i use to run a th350 in my built 400sbc truck with 1tons and 38" tires locked rear. never had a 1 problem .

and dont forget th400 eats 20-25 more hp than a th350 as it has more mass to spin up and get going.
 
i know i could build it to hold my engines power, im just looking at a price standpoint. Im on a college budget and it would cost me about 400 bucks to rebuild the 350 or for that price or less i could get a th400 that will definitely take it...idk im still undecided
 
transtar master reman kit .

noyoyo shift improver kit .

make sure baskets and pistions are set for max # of clutches.

reman convortor and good can cooler flush to rinse out cooler system .

thats what i had my buddy do for me . best bang for the buck .
 
sweetk30 said:
transtar master reman kit .

noyoyo shift improver kit .

make sure baskets and pistions are set for max # of clutches.

reman convortor and good can cooler flush to rinse out cooler system .

thats what i had my buddy do for me . best bang for the buck .
Click to expand...

and that held your 400 sbc. Mines gonna be putting out mid 400s for hp and about 500 ft lbs of torque.

When you say set for max number of clutches, i know its popular to increase the number of clutches, but how is that done? do you have to do machining or is it easier than that?
 
Make sure converter matches the cams RPM window. You cam supplier should be able to help you out with the correct stall and ect in helping you choose the correct converter.
 
my old 400sbc was built / balenced / knife edged crank / 40 over / good strong cam held just fine. it was removed from a ex drag car .

i use to spin it up all the time in muud/snow and i had 4.10 gears.

some baskets and pistions are setup for max # of clutches some are not. can be modifyed or find others set for it.

my buddy has run th350 for years behind his built 454 in his truck with 4.56 and 38" tires.
 
well that is definitely a thought then. Ive got a friend with a 350 behind a 454 and he beats on it.

So maybe the cheapest route is to just rebuild what i got. Ill keep thinking about it...thanks for all the info guys
 
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